bluuebunny/crossref_metadata_2025 huggingface dataset:
Sound transmission characteristics of Tee-junctions and the associated length corrections
Authors: Tang S. K.
Published: January 2004

The sound transmission characteristics of a Tee-junction formed by a sidebranch and an infinitely long duct are investigated numerically using the finite element method. The associated corrections of the branch length and the upstream duct length are also discussed in detail. The types of branch resonance that result in strong or weak sound transmission across the junction are determined and their effects on the length corrections examined. Results suggest that the type of sidebranch, the branch width, the branch length, and the order and the form of the resonance affect more significantly the length corrections of the duct section. The excitation of nonplanar higher branch modes gives rise to rapid increase in the duct length corrections and also results in lower sound transmission.
Detection and localization of inclusions in plates using inversion of point actuated surface displacements
Authors: Bucaro J. A. , Romano A. J. , Abraham P. , Dey S.
Published: January 2004

A numerical simulation is carried out demonstrating the use of plate surface vibration measurements for detecting and locating inclusions within the structure. A finite element code is used to calculate normal surface displacement for both steel and mortar plates subjected to a monochromatic point force. The data is generated for the homogeneous plate and the identical plate within which exists a small rectangular inclusion. It is observed that when the elastic modulus of the inclusion is orders of magnitude lower than the base material, resonances of the inclusion produce large local displacements that are readily observed in the raw displacement data. For more modest moduli differences, there are no such directly observable effects. In this case, three inverse algorithms are used to process the displacement data. The first two are local inversion techniques that each yield a spatial map of the elastic modulus normalized by density. These algorithms successfully detect and localize the inclusion based on its modulus difference from that of the base plate. The third technique uses a form of the inhomogeneous equation of motion to obtain the induced force distribution connected with the inclusion. The spatial mapping of this force also successfully detects and localizes the inclusion.
Local surface skimming longitudinal wave velocity and residual stress mapping
Authors: Sathish Shamachary , Martin Richard W. , Moran Thomas J.
Published: January 2004

Local variation in surface skimming longitudinal wave (SSLW) velocity has been measured using a scanning acoustic microscope. A very narrow width electrical impulse has been used to excite the transducer of the acoustic lens. This permits the separation of the SSLW signal from the direct reflected signal in the time domain. A simple method of measuring the time delay between the directly reflected signal and the SSLW signal at two defocuses has been utilized for the local measurement of SSLW velocity. The variation in the SSLW velocity measured over an area of the sample is scaled and presented as an image. The method has been implemented to image the variation of the SSLW velocity around a crack tip in a sample of Ti-6Al-4V. Since the SSLW velocity is known to change linearly with the stress, the SSLW velocity image is considered as a representation of the image of stress around the crack tip. Local stress variation in the same region of the crack tip is directly measured using x-ray diffraction. The SSLW velocity image is compared with the x-ray diffraction stress image. The contrast in the two images, spatial resolution, and the penetration depth into the sample of acoustic waves and x rays are discussed.
The sonar equation and the definitions of propagation loss
Authors: Ainslie Michael A.
Published: January 2004

A rigorous application of the traditional definition of sonar equation terms leads to the appearance of an unexpected factor, not routinely included, equal to the ratio of the characteristic impedance at the receiver to that at the source. An omission of this factor can lead to non-negligible errors for realistic conditions. It is further argued that a gradual change in the de facto definition of propagation loss occurred between 1965 and 1980. Two alternatives to the traditional sonar equation are suggested, each using one of the two propagation loss definitions and both eliminating the unwanted impedance ratio.
Methodology for rheological testing of engineered biomaterials at low audio frequencies
Authors: Titze Ingo R. , Klemuk Sarah A. , Gray Steven
Published: January 2004

A commercial rheometer (Bohlin CVO120) was used to mechanically test materials that approximate vocal-fold tissues. Application is to frequencies in the low audio range (20–150 Hz). Because commercial rheometers are not specifically designed for this frequency range, a primary problem is maintaining accuracy up to (and beyond) the mechanical resonance frequency of the rotating shaft assembly. A standard viscoelastic material (NIST SRM 2490) has been used to calibrate the rheometric system for an expanded frequency range. Mathematically predicted response curves are compared to measured response curves, and an error analysis is conducted to determine the accuracy to which the elastic modulus and the shear modulus can be determined in the 20–150-Hz region. Results indicate that the inertia of the rotating assembly and the gap between the plates need to be known (or determined empirically) to a high precision when the measurement frequency exceeds the resonant frequency. In addition, a phase correction is needed to account for the magnetic inertia (inductance) of the drag cup motor. Uncorrected, the measured phase can go below the theoretical limit of −π. This can produce large errors in the viscous modulus near and above the resonance frequency. With appropriate inertia and phase corrections, ±10% accuracy can be obtained up to twice the resonance frequency.
Cuing effects for informational masking
Authors: Richards Virginia M. , Neff Donna L.
Published: January 2004

The detection of a tone added to a random-frequency, multitone masker can be very poor even when the maskers have little energy in the frequency region of the signal. This paper examines the effects of adding a pretrial cue to reduce uncertainty for the masker or the signal. The first two experiments examined the effect of cuing a fixed-frequency signal as the number of masker components and presentation methods were manipulated. Cue effectiveness varied across observers, but could reduce thresholds by as much as 20 dB. Procedural comparisons indicated observers benefited more from having two masker samples to compare, with or without a signal cue, than having a single interval with one masker sample and a signal cue. The third experiment used random-frequency signals and compared no-cue, signal-cue, and masker-cue conditions, and also systematically varied the time interval between cue offset and trial onset. Thresholds with a cued random-frequency signal remained higher than for a cued fixed-frequency signal. For time intervals between the cue and trial of 50 ms or longer, thresholds were approximately the same with a signal or a masker cue and lower than when there was no cue. Without a cue or with a masker cue, analyses of possible decision strategies suggested observers attended to the potential signal frequencies, particularly the highest signal frequency. With a signal cue, observers appeared to attend to the frequency of the subsequent signal.
Measurement of dependence of backscatter coefficient from cylinders on frequency and diameter using focused transducers—with applications in trabecular bone
Authors: Wear Keith A.
Published: January 2004

A theory for the elastic scattering response from a cylinder insonified by a plane wave was previously derived by Faran. In the present paper, the empirical relationship between Faran’s theory and measurements of backscatter coefficient from cylindrical targets using focused transducers is investigated. Experimental measurements of dependence of backscatter coefficient on frequency and diameter for nylon wires are reported. It is found that, under certain conditions (including weak, incoherent scattering), backscatter coefficient measurements from collections of cylindrical scatterers may be meaningfully compared with Faran’s model predictions. At low frequencies, the theory and experimental measurements exhibit similar dependences on frequency and diameter, provided that the scatterers are not too densely packed. At higher frequencies, the fine structure of Faran’s predictions becomes difficult to reproduce experimentally with a focused transducer. Implications regarding applications to characterization of trabecular bone are discussed.
Representation of concurrent acoustic objects in primary auditory cortex
Authors: Dyson Benjamin J. , Alain Claude
Published: January 2004

Auditory scene analysis involves the simultaneous grouping and parsing of acoustic data into separate mental representations (i.e., objects). Over two experiments, we examined the sequence of neural processes underlying concurrent sound segregation by means of recording of human middle latency auditory evoked responses. Participants were presented with complex sounds comprising several harmonics, one of which could be mistuned such that it was not an integer multiple of the fundamental frequency. In both experiments, Na (approximately 22 ms) and Pa (approximately 32 ms) waves were reliably generated for all classes of stimuli. For stimuli with a fundamental frequency of 200 Hz, the mean Pa amplitude was significantly larger when the third harmonic was mistuned by 16% of its original value, relative to when it was tuned. The enhanced Pa amplitude was related to an increased likelihood in reporting the presence of concurrent auditory objects. Our results are consistent with a low-level stage of auditory scene analysis in which acoustic properties such as mistuning act as preattentive segregation cues that can subsequently lead to the perception of multiple auditory objects.
A model of acoustic interspeaker variability based on the concept of formant–cavity affiliation
Authors: Apostol Lian , Perrier Pascal , Bailly Gérard
Published: January 2004

A method is proposed to model the interspeaker variability of formant patterns for oral vowels. It is assumed that this variability originates in the differences existing among speakers in the respective lengths of their front and back vocal-tract cavities. In order to characterize, from the spectral description of the acoustic speech signal, these vocal-tract differences between speakers, each formant is interpreted, according to the concept of formant–cavity affiliation, as a resonance of a specific vocal-tract cavity. Its frequency can thus be directly related to the corresponding cavity length, and a transformation model can be proposed from a speaker A to a speaker B on the basis of the frequency ratios of the formants corresponding to the same resonances. In order to minimize the number of sounds to be recorded for each speaker in order to carry out this speaker transformation, the frequency ratios are exactly computed only for the three extreme cardinal vowels [i, a, u] and they are approximated for the remaining vowels through an interpolation function. The method is evaluated through its capacity to transform the (F1,F2) formant patterns of eight oral vowels pronounced by five male speakers into the (F1,F2) patterns of the corresponding vowels generated by an articulatory model of the vocal tract. The resulting formant patterns are compared to those provided by normalization techniques published in the literature. The proposed method is found to be efficient, but a number of limitations are also observed and discussed. These limitations can be associated with the formant–cavity affiliation model itself or with a possible influence of speaker-specific vocal-tract geometry in the cross-sectional direction, which the model might not have taken into account.
Reply to the Comment on “Multiple scattering in a reflecting cavity: Application to fish scattering” [J. Acoust. Soc. Am. 113, 2978–2979 (2003)] (L)
Authors: De Rosny Julien , Roux Philippe
Published: January 2004

In a recent letter, Ye and Chu comment on a previously published paper by the present authors [“Multiple scattering in a reflecting cavity: Application to fish counting in a tank,” J. Acoust. Soc. Am. 109, 2587–2597 (2001)]. This reply answers the questions asked in that letter and seeks to clarify some of the details in the original paper that may have led to a misunderstanding.
Wideband time-reversal imaging of an elastic target in an acoustic waveguide
Authors: Carin Lawrence , Liu Hongwei , Yoder Timothy , Couchman Luise , Houston Brian , Bucaro Joseph
Published: January 2004

Time-reversal is addressed for imaging elastic targets situated in an acoustic waveguide. It is assumed that the target-sensor range is large relative to the channel depth. We investigate the theory of wideband time-reversal imaging of an extended elastic target, for which the target dimensions are large relative to the principal wavelengths. When performing time-reversal imaging one requires a forward model for propagation through the channel, and the quality of the resulting image may be used as a measure of the match between the modeled and actual (measured) channel parameters. It is demonstrated that the channel parameters associated with a given measurement may be determined via a genetic-algorithm (GA) search in parameter space, employing a cost function based on the time-reversal image quality. Example GA channel-parameter-inversion results and imagery are presented for measured at-sea data.
Surface fields on nonseparable geometries
Authors: Sarkissian Angie
Published: January 2004

The field on the surface of a structure having nonseparable geometry may be expanded in a set of eigenfunctions suitable for that particular geometry. The eigenfunctions are computed numerically using the boundary elements method to compute a matrix that relates the field on the surface of the structure to its normal derivative at vanishing frequency and diagonalizing the matrix. The field on the surface of a finite cylinder with hemisphical end-caps is expanded in such a set of eigenfunctions for both a simple cylinder and a cylinder containing frames. Results for the framed cylinder is compared to Fourier decomposition of the field on the cylindrical portion of the structure.
Development of a new standard laboratory protocol for estimation of the field attenuation of hearing protection devices: Sample size necessary to provide acceptable reproducibility
Authors: Murphy William J. , Franks John R. , Berger Elliott H. , Behar Alberto , Casali John G. , Dixon-Ernst Christine , Krieg Edward F. , Mozo Ben T. , Royster Julia D. , Royster Larry H. , Simon Stephen D. , Stephenson Carol
Published: January 2004

The mandate of ASA Working Group S12/WG11 has been to develop “laboratory and/or field procedure(s) that yield useful estimates of field performance” of hearing protection devices (HPDs). A real-ear attenuation at threshold procedure was selected, devised, tested for one earmuff and three earplugs via an interlaboratory study involving five laboratories and 147 subjects, and incorporated into a new standard that was approved in 1997 [Royster et al., “Development of a new standard laboratory protocol for estimating the field attenuation of hearing protection devices. Part I. Research of Working Group 11, Accredited Standards Committee S12, Noise,” J. Acoust. Soc. Am. 99, 1506–1526; ANSI, S12.6-1997, “American National Standard method for measuring real-ear attenuation of hearing protectors” (American National Standards Institute, New York, 1997)]. The subject-fit methodology of ANSI S12.6-1997 relies upon listeners who are audiometrically proficient, but inexperienced in the use of HPDs. Whenever a new method is adopted, it is important to know the effects of variability on the power of the measurements. In evaluation of protector noise reduction determined by experimenter-fit, informed-user-fit, and subject-fit methods, interlaboratory reproducibility was found to be best for the subject-fit method. Formulas were derived for determining the minimum detectable difference between attenuation measurements and for determining the number of subjects necessary to achieve a selected level of precision. For a precision of 6 dB, the study found that the minimum number of subjects was 4 for the Bilsom UF-1 earmuff, 10 for the E⋅A⋅R Classic earplug, 31 for the Willson EP100 earplug, and 22 for the PlasMed V-51R earplug.
Effect of talker and speaking style on the Speech Transmission Index (L)
Authors: van Wijngaarden Sander J. , Houtgast Tammo
Published: January 2004

The Speech Transmission Index (STI) is routinely applied for predicting the intelligibility of messages (sentences) in noise and reverberation. Despite clear evidence that the STI is capable of doing so accurately, recent results indicate that the STI sometimes underestimates the effect of reverberation on sentence intelligibility. To investigate the influence of talker and speaking style, the Speech Reception Threshold in noise and reverberation was measured for three talkers, differing in clarity of articulation and speaking style. For very clear speech, the standard STI yields accurate results. For more conversational speech by an untrained talker, the effect of reverberation is underestimated. Measurements of the envelope spectrum reveal that conversational speech has relatively stronger contributions by higher (> 12.5 Hz) modulation frequencies. By modifying the STI calculation procedure to include modulations in the range 12.5–31.5 Hz, better results are obtained for conversational speech. A speaking-style-dependent choice for the STI modulation frequency range is proposed.
Spontaneous pattern formation in an acoustical resonator
Authors: Sánchez-Morcillo V. J.
Published: January 2004

A dynamical system of equations describing parametric sound generation (PSG) in a dispersive large aspect ratio resonator is derived. The model generalizes previously proposed descriptions of PSG by including diffraction effects and is analogous to the model used in theoretical studies of optical parametric oscillation. A linear stability analysis of the solution below the threshold of subharmonic generation reveals the existence of a pattern forming instability, which is confirmed by numerical integration. The conditions of emergence of periodic patterns in transverse space are discussed in the acoustical context.
Optimization of the performance of the sandwich piezoelectric ultrasonic transducer
Authors: Shuyu Lin
Published: January 2004

The resonance and antiresonance frequency, the effective electromechanical coupling coefficient, and the mechanical quality factor of a sandwich piezoelectric ultrasonic transducer are studied and optimized. The effect of the thickness of thick piezoelectric element electrodes on the transducer performance is analyzed. The effect of the length and position of the piezoelectric elements in the transducer is also studied. It is shown that, although using thick electrodes is beneficial for releasing heat produced by the piezoelectric elements, the effective electromechanical coupling coefficient and the mechanical quality factor are reduced. The length and the position of the piezoelectric elements affect the performances of the transducer. Increasing the length of the piezoelectric elements decreases the mechanical quality factor, but the effective electromechanical coupling coefficient increases. When the length reaches a certain value, the effective electromechanical coupling coefficient reaches a maximum value. When the piezoelectric elements are located at the geometrical center or the displacement node, the effective electromechanical coupling coefficient and the mechanical quality factor are maximized.
Sex differences in the acoustic structure of vowel-like grunt vocalizations in baboons and their perceptual discrimination by baboon listeners
Authors: Rendall Drew , Owren Michael J. , Weerts Elise , Hienz Robert D.
Published: January 2004

This study quantifies sex differences in the acoustic structure of vowel-like grunt vocalizations in baboons (Papio spp.) and tests the basic perceptual discriminability of these differences to baboon listeners. Acoustic analyses were performed on 1028 grunts recorded from 27 adult baboons (11 males and 16 females) in southern Africa, focusing specifically on the fundamental frequency (F0) and formant frequencies. The mean F0 and the mean frequencies of the first three formants were all significantly lower in males than they were in females, more dramatically so for F0. Experiments using standard psychophysical procedures subsequently tested the discriminability of adult male and adult female grunts. After learning to discriminate the grunt of one male from that of one female, five baboon subjects subsequently generalized this discrimination both to new call tokens from the same individuals and to grunts from novel males and females. These results are discussed in the context of both the possible vocal anatomical basis for sex differences in call structure and the potential perceptual mechanisms involved in their processing by listeners, particularly as these relate to analogous issues in human speech production and perception.
Determination of West Indian manatee vocalization levels and rate
Authors: Phillips Richard , Niezrecki Christopher , Beusse Diedrich O.
Published: January 2004

The West Indian manatee (Trichechus manatus latirostris) has become endangered partly because of a growing number of collisions with boats. A system to warn boaters of the presence of manatees, based upon the vocalizations of manatees, could potentially reduce these boat collisions. The feasibility of this warning system would depend mainly upon two factors: the rate at which manatees vocalize and the distance in which the manatees can be detected. The research presented in this paper verifies that the average vocalization rate of the West Indian manatee is approximately one to two times per 5-min period. Several different manatee vocalization recordings were broadcast to the manatees and their response was observed. It was found that during the broadcast periods, the vocalization rates for the manatees increased substantially when compared with the average vocalization rates during nonbroadcast periods. An array of four hydrophones was used while recording the manatees. This allowed for position estimation techniques to be used to determine the location of the vocalizing manatee. Knowing the position of the manatee, the source level was determined and it was found that the mean source level of the manatee vocalizations is approximately 112 dB (re 1 μPa) @ 1 m.
Nonperturbing measurements of spatially distributed underwater acoustic fields using a scanning laser Doppler vibrometer
Authors: Harland Andy R. , Petzing Jon N. , Tyrer John R.
Published: January 2004

Localized changes in the density of water induced by the presence of an acoustic field cause perturbations in the localized refractive index. This relationship has given rise to a number of nonperturbing optical metrology techniques for recording measurement parameters from underwater acoustic fields. A method that has been recently developed involves the use of a Laser Doppler Vibrometer (LDV) targeted at a fixed, nonvibrating, plate through an underwater acoustic field. Measurements of the rate of change of optical pathlength along a line section enable the identification of the temporal and frequency characteristics of the acoustic wave front. This approach has been extended through the use of a scanning LDV, which facilitates the measurement of a range of spatially distributed parameters. A mathematical model is presented that relates the distribution of pressure amplitude and phase in a planar wave front with the rate of change of optical pathlength measured by the LDV along a specifically orientated laser line section. Measurements of a 1 MHz acoustic tone burst generated by a focused transducer are described and the results presented. Graphical depictions of the acoustic power and phase distribution recorded by the LDV are shown, together with images representing time history during the acoustic wave propagation.
Prediction of ocean ambient sound generated from geophysical signals
Authors: Ma Barry , Nystuen Jeffrey , Lien Ren-Chieh
Published: January 2004

About 90 buoy months of ocean ambient sound data are collected using Acoustic Rain Gauges in different open-ocean locations. Distinct ambient sound spectra are identified through a series of discrimination process. Some distinct features are described as follows: (1) Excluding effects of rain, observed ambient sound spectra, generated exclusively by wind, exhibit a constant frequency spectral slope in 1–35 kHz. (2) Drizzle produces a prominent spectral peak at 15 kHz, and the magnitude of the spectral peak is very sensitive to the wind speed. These are consistent with earlier findings [Vagle et al. (1990) and Nystuen (1993)]. (3) Preliminary analysis shows that the spectral slope between 1–10 kHz decreases linearly with the rainfall rate. Therefore, the rainfall rate may be reliably predicted by both the spectral slope and the spectral magnitude in 1–10 kHz frequency range. The comparison of these two independent predictions provides the quality check of the estimate of the rainfall rate. An analytical spectral model of the ocean ambient sound from 1–50 kHz is constructed using two input parameters, rainfall rate and wind speed, based on the existing observations. This analytical model is aimed at predicting the ambient sound spectra at varying rainfall rates and wind speeds.
Sonoelastography imaging: Principles and practices
Authors: Taylor Lawrence S. , Rubens Deborah J. , Parker Kevin J.
Published: January 2004

Vibration amplitude sonoelastography imaging is an ultrasound imaging technique in which low frequency (100–500 Hz), low amplitude shear waves are propagated deep into tissue, while real time color Doppler techniques are used to image the resulting vibration field. A radio frequency ultrasound signal is phase modulated by a vibrating particle such that the peak vibration amplitude is directly proportional to the spread (standard deviation) of its power spectrum. A key application for this technique is the detection and imaging of small lesions. Finite element studies predict that a discrete hard inhomogeneity present within a larger region of soft tissue will cause a decrease in the vibration field at the location of the inhomogeneity. The inhomogeneity is made visible as a region of low vibration in the color Doppler image. The principles and practices of this technique are reviewed and results are shown for the detection and imaging of stiff thermal lesions induced in bovine calf liver.
Relationships between objective acoustic indices and acoustic comfort evaluation in nonacoustic spaces
Authors: Kang Jian
Published: January 2004

Much attention has been paid to acoustic spaces such as concert halls and recording studios, whereas research on nonacoustic buildings/spaces has been rather limited, especially from the viewpoint of acoustic comfort. In this research a series of case studies has been carried out on this topic, considering various spaces including shopping mall atrium spaces, library reading rooms, football stadia, swimming spaces, churches, dining spaces, as well as urban open public spaces. The studies focus on the relationships between objective acoustic indices such as sound pressure level and reverberation time and perceptions of acoustic comfort. The results show that the acoustic atmosphere is an important consideration in such spaces and the evaluation of acoustic comfort may vary considerably even if the objective acoustic indices are the same. It is suggested that current guidelines and technical regulations are insufficient in terms of acoustic design of these spaces, and the relationships established from the case studies between objective and subjective aspects would be useful for developing further design guidelines. [Work supported partly by the British Academy.]
Characterization of Multiple-Antimicrobial-Resistant
Salmonella
Serovars Isolated from Retail Meats
Authors: Chen Sheng , Zhao Shaohua , White David G. , Schroeder Carl M. , Lu Ran , Yang Hanchun , McDermott Patrick F. , Ayers Sherry , Meng Jianghong
Published: January 2004

A total of 133
Salmonella
isolates recovered from retail meats purchased in the United States and the People's Republic of China were assayed for antimicrobial susceptibility, the presence of integrons and antimicrobial resistance genes, and horizontal transfer of characterized antimicrobial resistance determinants via conjugation. Seventy-three (82%) of these
Salmonella
isolates were resistant to at least one antimicrobial agent. Resistance to the following antibiotics was common among the United States isolates: tetracycline (68% of the isolates were resistant), streptomycin (61%), sulfamethoxazole (42%), and ampicillin (29%). Eight
Salmonella
isolates (6%) were resistant to ceftriaxone. Fourteen isolates (11%) from the People's Republic of China were resistant to nalidixic acid and displayed decreased susceptibility to ciprofloxacin. A total of 19 different antimicrobial resistance genes were identified in 30 multidrug-resistant
Salmonella
isolates. The
bla
CMY-2
gene, encoding a class A AmpC β-lactamase, was detected in all 10
Salmonella
isolates resistant to extended-spectrum β-lactams. Resistance to ampicillin was most often associated with a TEM-1 family β-lactamase gene. Six aminoglycoside resistance genes,
aadA1
,
aadA2
,
aacC2
,
Kn
,
aph
(
3
)
-IIa
, and
aac
(
3
)
-IVa
, were commonly present in the
Salmonella
isolates. Sixteen (54%) of 30
Salmonella
isolates tested had integrons ranging in size from 0.75 to 2.7 kb. Conjugation studies demonstrated that there was plasmid-mediated transfer of genes encoding CMY-2 and TEM-1-like β-lactamases. These data indicate that
Salmonella
isolates recovered from retail raw meats are commonly resistant to multiple antimicrobials, including those used for treating salmonellosis, such as ceftriaxone. Genes conferring antimicrobial resistance in
Salmonella
are often carried on integrons and plasmids and could be transmitted through conjugation. These mobile DNA elements have likely played an important role in transmission and dissemination of antimicrobial resistance determinants among
Salmonella
strains.
Genetics of Zwittermicin A Production by
Bacillus cereus
Authors: Emmert Elizabeth A. B. , Klimowicz Amy K. , Thomas Michael G. , Handelsman Jo
Published: January 2004

Zwittermicin A represents a new chemical class of antibiotic and has diverse biological activities, including suppression of oomycete diseases of plants and potentiation of the insecticidal activity of
Bacillus thuringiensis
. To identify genes involved in zwittermicin A production, we generated 4,800 transposon mutants of
B. cereus
UW101C and screened them for zwittermicin A accumulation. Nine mutants did not produce detectable zwittermicin A, and one mutant produced eightfold more than the parent strain. The DNA flanking the transposon insertions in six of the nine nonproducing mutants contains significant sequence similarity to genes involved in peptide and polyketide antibiotic biosynthesis. The mutant that overproduced zwittermicin A contained a transposon insertion immediately upstream from a gene that encodes a deduced protein that is a member of the MarR family of transcriptional regulators. Three genes identified by the mutant analysis mapped to a region that was previously shown to carry the zwittermicin A self-resistance gene,
zmaR
, and a biosynthetic gene (E. A. Stohl, J. L. Milner, and J. Handelsman, Gene 237:403-411, 1999). Further sequencing of this region revealed genes proposed to encode zwittermicin A precursor biosynthetic enzymes, in particular, those involved in the formation of the aminomalonyl- and hydroxymalonyl-acyl carrier protein intermediates. Additionally, nonribosomal peptide synthetase (NRPS) and polyketide synthase (PKS) homologs are present, suggesting that zwittermicin A is synthesized by a mixed NRPS/PKS pathway.
Structure and Characterization of Flavolipids, a Novel Class of Biosurfactants Produced by
Flavobacterium
sp. Strain MTN11
Authors: Bodour Adria A. , Guerrero-Barajas Claudia , Jiorle Beth V. , Malcomson Mark E. , Paull Amanda K. , Somogyi Arpad , Trinh Long N. , Bates Robert B. , Maier Raina M.
Published: January 2004

Herein we report the structure and selected properties of a new class of biosurfactants that we have named the flavolipids. The flavolipids exhibit a unique polar moiety that features citric acid and two cadaverine molecules. Flavolipids were produced by a soil isolate,
Flavobacterium
sp. strain MTN11 (accession number
AY162137
), during growth in mineral salts medium, with 2% glucose as the sole carbon and energy source. MTN11 produced a mixture of at least 37 flavolipids ranging from 584 to 686 in molecular weight (MW). The structure of the major component (23%; MW = 668) was determined to be 4-[[5-(7-methyl-(
E
)-2-octenoylhydroxyamino)pentyl]amino]-2-[2-[[5-(7-methyl-(
E
)-2-octenoylhydroxyamino)pentyl]amino]-2-oxoethyl]-2-hydroxy-4-oxobutanoic acid. The partially purified flavolipid mixture isolated from strain MTN11 exhibited a critical micelle concentration of 300 mg/liter and reduced surface tension to 26.0 mN/m, indicating strong surfactant activity. The flavolipid mixture was a strong and stable emulsifier even at concentrations as low as 19 mg/liter. It was also an effective solubilizing agent, and in a biodegradation study, it enhanced hexadecane mineralization by two isolates, MTN11 (100-fold) and
Pseudomonas aeruginosa
ATCC 9027 (2.5-fold), over an 8-day period. The flavolipid-cadmium stability constant was measured to be 3.61, which is comparable to that for organic ligands such as oxalic acid and acetic acid. In summary, the flavolipids represent a new class of biosurfactants that have potential for use in a variety of biotechnological and industrial applications.
Enzymatic Assimilation of Cyanide via Pterin-Dependent Oxygenolytic Cleavage to Ammonia and Formate in
Pseudomonas fluorescens
NCIMB 11764
Authors: Fernandez Ruby F. , Dolghih Elena , Kunz Daniel A.
Published: January 2004

Utilization of cyanide as a nitrogen source by
Pseudomonas fluorescens
NCIMB 11764 occurs via oxidative conversion to carbon dioxide and ammonia, with the latter compound satisfying the nitrogen requirement. Substrate attack is initiated by cyanide oxygenase (CNO), which has been shown previously to have properties of a pterin-dependent hydroxylase. CNO was purified 71-fold and catalyzed the quantitative conversion of cyanide supplied at micromolar concentrations (10 to 50 μM) to formate and ammonia. The specific activity of the partially purified enzyme was approximately 500 mU/mg of protein. The pterin requirement for activity could be satisfied by supplying either the fully (tetrahydro) or partially (dihydro) reduced forms of various pterin compounds at catalytic concentrations (0.5 μM). These compounds included, for example, biopterin, monapterin, and neopterin, all of which were also identified in cell extracts. Substrate conversion was accompanied by the consumption of 1 and 2 molar equivalents of molecular oxygen and NADH, respectively. When coupled with formate dehydrogenase, the complete enzymatic system for cyanide oxidation to carbon dioxide and ammonia was reconstituted and displayed an overall reaction stoichiometry of 1:1:1 for cyanide, O
2
, and NADH consumed. Cyanide was also attacked by CNO at a higher concentration (1 mM), but in this case formamide accumulated as the major reaction product (formamide/formate ratio, 0.6:0.3) and was not further degraded. A complex reaction mechanism involving the production of isocyanate as a potential CNO monooxygenation product is proposed. Subsequent reduction of isocyanate to formamide, whose hydrolysis occurs as a CNO-bound intermediate, is further envisioned. To our knowledge, this is the first report of enzymatic conversion of cyanide to formate and ammonia by a pterin-dependent oxygenative mechanism.
Effects of Polyunsaturated Fatty Acids in Growth Medium on Lipid Composition and on Physicochemical Surface Properties of Lactobacilli
Authors: Kankaanpää P. , Yang B. , Kallio H. , Isolauri E. , Salminen S.
Published: January 2004

Most probiotic lactobacilli adhere to intestinal surfaces, a phenomenon influenced by free polyunsaturated fatty acids (PUFA). The present study investigated whether free linoleic acid, γ-linolenic acid, arachidonic acid, α-linolenic acid, or docosahexaenoic acid in the growth medium alters the fatty acid composition of lactobacilli and their physical characteristics. The most abundant bacterial fatty acids identified were oleic, vaccenic, and dihydrosterculic acids. PUFA, especially conjugated linoleic acid (CLA) isomers and γ-linolenic, eicosapentaenoic, docosahexaenoic, and α-linolenic acids, also were identified in lactobacilli. When lactobacilli were cultured in MRS broth supplemented with various free PUFA, the incorporation of a given PUFA into bacterial fatty acids was clearly observed. Moreover, PUFA supplementation also resulted in PUFA-dependent changes in the proportions of other fatty acids; major interconversions were seen in octadecanoic acids (18:1), their methylenated derivatives (19:cyc), and CLA. Intermittent changes in eicosapentaenoic acid proportions also were noted. These results were paralleled by minor changes in the hydrophilic or hydrophobic characteristics of lactobacilli, suggesting that PUFA interfere with microbial adhesion to intestinal surfaces through other mechanisms. In conclusion, we have demonstrated that free PUFA in the growth medium induce changes in bacterial fatty acids in relation to the regulation of the degree of fatty acid unsaturation, cyclization, and proportions of CLA and PUFA containing 20 to 22 carbons. The potential role of lactobacilli as regulators of PUFA absorption may represent another means by which probiotics could redirect the delicate balance of inflammatory mediators derived from PUFA within the inflamed intestine.
Molecular Cloning and Expression inSaccharomyces cerevisiaeof a Laccase Gene from the AscomyceteMelanocarpus albomyces
Authors: Kiiskinen Laura-Leena , Saloheimo Markku
Published: January 2004

Thelac1gene encoding an extracellular laccase was isolated from the thermophilic fungusMelanocarpus albomyces. This gene has five introns, and it encodes a protein consisting of 623 amino acids. The deduced amino acid sequence of the laccase was shown to have high homology with laccases from other ascomycetes. In addition to removal of a putative 22-amino-acid signal sequence and a 28-residue propeptide, maturation of the translation product oflac1was shown to involve cleavage of a C-terminal 14-amino-acid extension.M. albomyces lac1cDNA was expressed inSaccharomyces cerevisiaeunder the inducibleGAL1promoter. Extremely low production was obtained with the expression construct containing laccase cDNA with its own signal and propeptide sequences. The activity levels were significantly improved by replacing these sequences with the prepro sequence of theS. cerevisiaeα-factor gene. The role of the C-terminal extension in laccase production inS. cerevisiaewas also studied. Laccase production was increased sixfold with the modified cDNA that had a stop codon after the native processing site at the C terminus.
Sequence Analysis of Amplified DNA Fragments Containing the Region Encoding the Putative Lipase Substrate-Binding Domain and Genotyping of
Aeromonas hydrophila
Authors: Watanabe Noboru , Morita Koji , Furukawa Tomoko , Manzoku Taki , Endo Eiko , Kanamori Masato
Published: January 2004

DNA fragments were amplified by PCR from all tested strains of
Aeromonas hydrophila
,
A. caviae
, and
A. sobria
with primers designed based on sequence alignment of all lipase, phospholipase C, and phospholipase A1 genes and the cytotonic enterotoxin gene, all of which have been reported to have the consensus region of the putative lipase substrate-binding domain. All strains showed lipase activity, and all amplified DNA fragments contained a nucleotide sequence corresponding to the substrate-binding domain. Thirty-five distinct nucleotide sequence patterns and 15 distinct deduced amino acid sequence patterns were found in the amplified DNA fragments from 59
A. hydrophila
strains. The deduced amino acid sequences of the amplified DNA fragments from
A. caviae
and
A. sobria
strains had distinctive amino acids, suggesting a species-specific sequence in each organism. Furthermore, the amino acid sequence patterns appear to differ between clinical and environmental isolates among
A. hydrophila
strains. Some strains whose nucleotide sequences were identical to one another in the amplified region showed an identical DNA fingerprinting pattern by repetitive extragenic palindromic sequence-PCR genotyping. These results suggest that
A. hydrophila
, and also
A. caviae
and
A. sobria
strains, have a gene encoding a protein with lipase activity. Homologs of the gene appear to be widely distributed in
Aeromonas
strains, probably associating with the evolutionary genetic difference between clinical and environmental isolates of
A. hydrophila
. Additionally, the distinctive nucleotide sequences of the genes could be attributed to the genotype of each strain, suggesting that their analysis may be helpful in elucidating the genetic heterogeneity of
Aeromonas
.
Detection ofSalmonella entericaSerovar Typhimurium by Using a Rapid, Array-Based Immunosensor
Authors: Taitt Chris Rowe , Shubin Yura S. , Angel Roselina , Ligler Frances S.
Published: January 2004

The multianalyte array biosensor (MAAB) is a rapid analysis instrument capable of detecting multiple analytes simultaneously. Rapid (15-min), single-analyte sandwich immunoassays were developed for the detection ofSalmonella entericaserovar Typhimurium, with a detection limit of 8 × 104CFU/ml; the limit of detection was improved 10-fold by lengthening the assay protocol to 1 h.S. entericaserovar Typhimurium was also detected in the following spiked foodstuffs, with minimal sample preparation: sausage, cantaloupe, whole liquid egg, alfalfa sprouts, and chicken carcass rinse. Cross-reactivity tests were performed withEscherichia coliandCampylobacter jejuni. To determine whether the MAAB has potential as a screening tool for the diagnosis of asymptomaticSalmonellainfection of poultry, chicken excretal samples from a private, noncommercial farm and from university poultry facilities were tested. While the private farm excreta gave rise to signals significantly above the buffer blanks, none of the university samples tested positive forS. entericaserovar Typhimurium without spiking; dose-response curves of spiked excretal samples from university-raised poultry gave limits of detection of 8 × 103CFU/g.
Directed Evolution of Pyruvate Decarboxylase-Negative
Saccharomyces cerevisiae
, Yielding a C
2
-Independent, Glucose-Tolerant, and Pyruvate-Hyperproducing Yeast
Authors: van Maris Antonius J. A. , Geertman Jan-Maarten A. , Vermeulen Alexander , Groothuizen Matthijs K. , Winkler Aaron A. , Piper Matthew D. W. , van Dijken Johannes P. , Pronk Jack T.
Published: January 2004

The absence of alcoholic fermentation makes pyruvate decarboxylase-negative (Pdc
−
) strains of
Saccharomyces cerevisiae
an interesting platform for further metabolic engineering of central metabolism. However, Pdc
−
S. cerevisiae
strains have two growth defects: (i) growth on synthetic medium in glucose-limited chemostat cultures requires the addition of small amounts of ethanol or acetate and (ii) even in the presence of a C
2
compound, these strains cannot grow in batch cultures on synthetic medium with glucose. We used two subsequent phenotypic selection strategies to obtain a Pdc
−
strain without these growth defects. An acetate-independent Pdc
−
mutant was obtained via (otherwise) glucose-limited chemostat cultivation by progressively lowering the acetate content in the feed. Transcriptome analysis did not reveal the mechanisms behind the C
2
independence. Further selection for glucose tolerance in shake flasks resulted in a Pdc
−
S. cerevisiae
mutant (TAM) that could grow in batch cultures (μ
max
= 0.20 h
−1
) on synthetic medium, with glucose as the sole carbon source. Although the exact molecular mechanisms underlying the glucose-tolerant phenotype were not resolved, transcriptome analysis of the TAM strain revealed increased transcript levels of many glucose-repressible genes relative to the isogenic wild type in nitrogen-limited chemostat cultures with excess glucose. In pH-controlled aerobic batch cultures, the TAM strain produced large amounts of pyruvate. By repeated glucose feeding, a pyruvate concentration of 135 g liter
−1
was obtained, with a specific pyruvate production rate of 6 to 7 mmol g of biomass
−1
h
−1
during the exponential-growth phase and an overall yield of 0.54 g of pyruvate g of glucose
−1
.
Quantitative PCR with 16S rRNA-Gene-Targeted Species-Specific Primers for Analysis of Human Intestinal Bifidobacteria
Authors: Matsuki Takahiro , Watanabe Koichi , Fujimoto Junji , Kado Yukiko , Takada Toshihiko , Matsumoto Kazumasa , Tanaka Ryuichiro
Published: January 2004

A highly sensitive quantitative PCR detection method has been developed and applied to the distribution analysis of human intestinal bifidobacteria by combining real-time PCR withBifidobacteriumgenus- and species-specific primers. Real-time PCR detection of serially diluted DNA extracted from cultured bifidobacteria was linear for cell counts ranging from 106to 10 cells per PCR assay. It was also found that the method was applicable to the detection ofBifidobacteriumin feces when it was present at concentrations of >106cells per g of feces. Concerning the distribution ofBifidobacteriumspecies in intestinal flora, theBifidobacterium adolescentisgroup, theBifidobacterium catenulatumgroup, andBifidobacterium longumwere found to be the three predominant species by examination of DNA extracted from the feces of 46 healthy adults. We also examined changes in the population and composition ofBifidobacteriumspecies in human intestinal flora of six healthy adults over an 8-month period. The results showed that the composition of bifidobacterial flora was basically stable throughout the test period.
Metabolism of 2,2′- and 3,3′-Dihydroxybiphenyl by the Biphenyl Catabolic Pathway of
Comamonas testosteroni
B-356
Authors: Sondossi M. , Barriault D. , Sylvestre M.
Published: January 2004

The purpose of this investigation was to examine the capacity of the biphenyl catabolic enzymes of
Comamonas testosteroni
B-356 to metabolize dihydroxybiphenyls symmetrically substituted on both rings. Data show that 3,3′-dihydroxybiphenyl is by far the preferred substrate for strain B-356. However, the dihydrodiol metabolite is very unstable and readily tautomerizes to a dead-end metabolite or is dehydroxylated by elimination of water. The tautomerization route is the most prominent. Thus, a very small fraction of the substrate is converted to other hydroxylated and acidic metabolites. Although 2,2′-dihydroxybiphenyl is a poor substrate for strain B-356 biphenyl dioxygenase, metabolites were produced by the biphenyl catabolic enzymes, leading to production of 2-hydroxybenzoic acid. Data show that the major route of metabolism involves, as a first step, a direct dehydroxylation of one of the
ortho
-substituted carbons to yield 2,3,2′-trihydroxybiphenyl. However, other metabolites resulting from hydroxylation of carbons 5 and 6 of 2,2′-dihydroxybiphenyl were also produced, leading to dead-end metabolites.