bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modified
Bacillus thuringiensis
Toxins and a Hybrid
B. thuringiensis
Strain Counter Greenhouse-Selected Resistance in
Trichoplusia ni
Authors: Franklin Michelle T. , Nieman Christal L. , Janmaat Alida F. , Soberón Mario , Bravo Alejandra , Tabashnik Bruce E. , Myers Judith H. 
Published: July 2009

ABSTRACT

Resistance of greenhouse-selected strains of the cabbage looper,
Trichoplusia ni
, to
Bacillus thuringiensis
subsp.
kurstaki
was countered by a hybrid strain of
B. thuringiensis
and genetically modified toxins Cry1AbMod and Cry1AcMod, which lack helix α-1. Resistance to Cry1AbMod and Cry1AcMod was >100-fold less than resistance to native toxins Cry1Ab and Cry1Ac.
Regulatory Phenotyping Reveals Important Diversity within the Species
Lactococcus lactis
Authors: Bachmann Herwig , Starrenburg Marjo J. C. , Dijkstra Annereinou , Molenaar Douwe , Kleerebezem Michiel , Rademaker Jan L. W. , van Hylckama Vlieg Johan E. T. 
Published: July 2009

ABSTRACT

The diversity in regulatory phenotypes among a collection of 84
Lactococcus lactis
strains isolated from dairy and nondairy origin was explored. The specific activities of five enzymes were assessed in cell extracts of all strains grown in two different media, a nutritionally rich broth and a relatively poor chemically defined medium. The five investigated enzymes, branched chain aminotransferase (BcaT), aminopeptidase N (PepN), X-prolyl dipeptidyl peptidase (PepX), alpha-hydroxyisocaproic acid dehydrogenase (HicDH), and esterase, are involved in nitrogen and fatty acid metabolism and catalyze key steps in the production of important dairy flavor compounds. The investigated cultures comprise 75
L. lactis
subsp.
lactis
isolates (including 7
L. lactis
subsp.
lactis
biovar diacetylactis isolates) and 9
L. lactis
subsp.
c
remoris
isolates. All
L. lactis
subsp.
cremoris
and 22
L. lactis
subsp.
lactis
(including 6
L. lactis
subsp.
lactis
biovar diacetylactis) cultures originated from a dairy environment. All other cultures originated from (fermented) plant materials and were isolated at different geographic locations. Correlation analysis of specific enzyme activities revealed significantly different regulatory phenotypes for dairy and nondairy isolates. The enzyme activities in the two investigated media were in general poorly correlated and revealed a high degree of regulatory diversity within this collection of closely related strains. To the best of our knowledge, these results represent the most extensive diversity analysis of regulatory phenotypes within a single bacterial species to date. The presented findings underline the importance of the availability of screening procedures for, e.g., industrially relevant enzyme activities in models closely mimicking application conditions. Moreover, they corroborate the notion that regulatory changes are important drivers of evolution.
Potential Applicability of Chymotrypsin-Susceptible Microcin J25 Derivatives to Food Preservation
Authors: Pomares María Fernanda , Salomón Raúl A. , Pavlova Olga , Severinov Konstantin , Farías Ricardo , Vincent Paula A. 
Published: July 2009

ABSTRACTMicrocin J25 (MccJ25) is a 21-residue ribosomally synthesized lariat peptide antibiotic. MccJ25 is active against such food-borne disease-causing pathogens asSalmonellaspp.,Shigellaspp., andEscherichia coli, includingE. coliO157:H7 and non-O157 strains. MccJ25 is highly resistant to digestion by proteolytic enzymes present in the stomach and intestinal contents. MccJ25 would therefore remain active in the gastrointestinal tract, affecting normal intestinal microbiota, and this limits the potential use of MccJ25 as a food preservative. In the present paper, we describe a chymotrypsin-susceptible MccJ25 derivative with a mutation of Gly12to Tyr that retained almost full antibiotic activity and efficiently inhibited the growth of pathogenicSalmonella entericaserovar Newport andEscherichia coliO157:H7 in skim milk and egg yolk. However, unlike the wild-type MccJ25, the MccJ25(G12Y) variant was inactivated by digestive enzymes both in vitro and in vivo. To our knowledge, our results represent the first example of a rational modification of a microcin aimed at increasing its potential use in food preservation.
Complete WO Phage Sequences Reveal Their Dynamic Evolutionary Trajectories and Putative Functional Elements Required for Integration into theWolbachiaGenome
Authors: Tanaka Kohjiro , Furukawa Seiichi , Nikoh Naruo , Sasaki Tetsuhiko , Fukatsu Takema 
Published: July 2009

ABSTRACTWolbachiaendosymbionts are ubiquitously found in diverse insects including many medical and hygienic pests, causing a variety of reproductive phenotypes, such as cytoplasmic incompatibility, and thereby efficiently spreading in host insect populations. Recently,Wolbachia-mediated approaches to pest control and management have been proposed, but the application of these approaches has been hindered by the lack of genetic transformation techniques for symbiotic bacteria. Here, we report the genome and structure of active bacteriophages from aWolbachiaendosymbiont. From theWolbachiastrainwCauB infecting the mothEphestia kuehniellatwo closely related WO prophages, WOcauB2 of 43,016 bp with 47 open reading frames (ORFs) and WOcauB3 of 45,078 bp with 46 ORFs, were characterized. In each of the prophage genomes, an integrase gene and an attachment site core sequence were identified, which are putatively involved in integration and excision of the mobile genetic elements. The 3′ region of the prophages encoded genes with sequence motifs related to bacterial virulence and protein-protein interactions, which might represent effector molecules that affect cellular processes and functions of their host bacterium and/or insect. Database searches and phylogenetic analyses revealed that the prophage genes have experienced dynamic evolutionary trajectories. Genes similar to the prophage genes were found across divergent bacterial phyla, highlighting the active and mobile nature of the genetic elements. We suggest that the active WO prophage genomes and their constituent sequence elements would provide a clue to development of a genetic transformation vector forWolbachiaendosymbionts.
Inter- and Intraspecies Plasmid-Mediated Transfer of Florfenicol Resistance in
Enterobacteriaceae
Isolates from Swine
Authors: Rayamajhi Nabin , Cha Seung Bin , Kang Mi Lan , Lee Su In , Lee Hee Soo , Yoo Han Sang 
Published: July 2009

ABSTRACT
Florfenicol resistance was analyzed in 230 enteric pig isolates collected between 1998 and 2006. PCR, plasmid profiling, Southern blot hybridization, and a mixed-broth conjugation assay suggested the intra- and interspecies plasmid-mediated transfer of florfenicol resistance among the isolates that exhibited MICs for florfenicol between 4 to 128 mg/liter.
Outwardly Rectifying Anionic Channel from the Plasma Membrane of the Fungus
Phycomyces blakesleeanus
Authors: Živić Miroslav , Popović Marko , Todorović Nataša , Vučinić Željko 
Published: July 2009

ABSTRACT

In the present report, by using a patch clamp technique, we provide, to our knowledge, the first detailed description of an anionic channel from filamentous fungi. The characterized channel, an outwardly rectifying anionic channel (ORAC), is the most prominent feature of the cell membrane of the fungus
Phycomyces blakesleeanus
in the absence of energizing substrates. The unitary conductance of the channel is 11.3 ± 0.4 pS. It is characterized by a strong voltage dependence of the open-channel probability (
z
δ; the gating charge is 2.1 ± 0.1), and the channel is activated by depolarization. The values of the time constants for voltage-induced activation and deactivation of 28 ± 3 ms for τ

a

and 39 ± 9 ms for τ

d

show that the ORAC is characterized by fast activation/deactivation kinetics. The ORAC shows strong selectivity for anions over cations and weak selectivity among anions, with a selectivity sequence of I
−
≥ NO
3
−
> Br
−
> Cl
−
> SO
4
2−
= 4.8 > 4.4 > 2.2 > 1 > 0.55, which corresponds to Eisenman series 1. The channel is characterized by two open and two closed states, with dominant long open (τ
o2
= 35.0 ± 3.9 ms) and long closed (τ
c2
= 166 ± 28 ms) states occupying 63% ± 8% and 79% ± 3% of total open and closed times, respectively. The ORAC is insensitive to anthracene-9-carboxylic acid (<200 μM), but 2 mM malate reversibly inhibits 59% ± 12% of the channel activity. Based on the electrophysiological properties of the channel, we propose that the ORAC plays a role in anion accumulation and in membrane potential regulation through local membrane depolarization.
Swarming ofPseudomonas aeruginosaIs Controlled by a Broad Spectrum of Transcriptional Regulators, Including MetR
Authors: Yeung Amy T. Y. , Torfs Ellen C. W. , Jamshidi Farzad , Bains Manjeet , Wiegand Irith , Hancock Robert E. W. , Overhage Joerg 
Published: July 2009

ABSTRACTPseudomonas aeruginosaexhibits swarming motility on semisolid surfaces (0.5 to 0.7% agar). Swarming is a more than just a form of locomotion and represents a complex adaptation resulting in changes in virulence gene expression and antibiotic resistance. In this study, we used a comprehensiveP. aeruginosaPA14 transposon mutant library to investigate how the complex swarming adaptation process is regulated. A total of 233P. aeruginosaPA14 transposon mutants were verified to have alterations in swarming motility. The swarming-associated genes functioned not only in flagellar or type IV pilus biosynthesis but also in processes as diverse as transport, secretion, and metabolism. Thirty-three swarming-deficient and two hyperswarming mutants had transposon insertions in transcriptional regulator genes, including genes encoding two-component sensors and response regulators; 27 of these insertions were newly identified. Of the 25 regulatory mutants whose swarming motility was highly impaired (79 to 97%), only 1 (a PA1458 mutant) had a major defect in swimming, suggesting that this regulator might influence flagellar synthesis or function. Twitching motility, which requires type IV pili, was strongly affected in only two regulatory mutants (pilHand PA2571 mutants) and was moderately affected in three other mutants (algR,ntrB, andnosRmutants). Microarray analyses were performed to compare the gene expression profile of a swarming-deficient PA3587 mutant to that of the wild-type PA14 strain under swarming conditions. PA3587 showed 63% homology tometR, which encodes a regulator of methionine biosynthesis inEscherichia coli. The observed dysregulation in themetRmutant of nine different genes required for swarming motility provided a possible explanation for the swarming-deficient phenotype of this mutant.
GidA Posttranscriptionally Regulates
rhl
Quorum Sensing in
Pseudomonas aeruginosa
Authors: Gupta Rashmi , Gobble Timothy R. , Schuster Martin 
Published: July 2009

ABSTRACT

The opportunistic pathogen
Pseudomonas aeruginosa
utilizes two interconnected acyl-homoserine lactone quorum-sensing (acyl-HSL QS) systems, LasRI and RhlRI, to regulate the expression of hundreds of genes. The QS circuitry itself is integrated into a complex network of regulation by other factors. However, our understanding of this network is still unlikely to be complete, as a comprehensive, saturating approach to identifying regulatory components has never been attempted. Here, we utilized a nonredundant
P. aeruginosa
PA14 transposon library to identify additional genes that regulate QS at the level of LasRI/RhlRI. We initially screened all 5,459 mutants for loss of function in one QS-controlled trait (skim milk proteolysis) and then rescreened attenuated candidates for defects in other QS phenotypes (LasA protease, rhamnolipid, and pyocyanin production) to exclude mutants defective in functions other than QS. We identified several known and novel genes, but only two novel genes,
gidA
and
pcnB
, affected all of the traits assayed. We characterized
gidA
, which exhibited the most striking QS phenotypes, further. This gene is predicted to encode a conserved flavin adenine dinucleotide-binding protein involved in tRNA modification. Inactivation of the gene primarily affected
rhlR
-dependent QS phenotypes such as LasA, pyocyanin, and rhamnolipid production. GidA affected RhlR protein but not transcript levels and also had no impact on LasR and acyl-HSL production. Overexpression of
rhlR
in a
gidA
mutant partially restored QS-dependent phenotypes. Taken together, these results indicate that GidA selectively controls QS gene expression posttranscriptionally via RhlR-dependent and -independent pathways.
Hopanoids Play a Role in Membrane Integrity and pH Homeostasis in
Rhodopseudomonas palustris
TIE-1
Authors: Welander Paula V. , Hunter Ryan C. , Zhang Lichun , Sessions Alex L. , Summons Roger E. , Newman Dianne K. 
Published: July 2009

ABSTRACT

Sedimentary hopanes are pentacyclic triterpenoids that serve as biomarker proxies for bacteria and certain bacterial metabolisms, such as oxygenic photosynthesis and aerobic methanotrophy. Their parent molecules, the bacteriohopanepolyols (BHPs), have been hypothesized to be the bacterial equivalent of sterols. However, the actual function of BHPs in bacterial cells is poorly understood. Here, we report the physiological study of a mutant in
Rhodopseudomonas palustris
TIE-1 that is unable to produce any hopanoids. The deletion of the gene encoding the squalene-hopene cyclase protein (Shc), which cyclizes squalene to the basic hopene structure, resulted in a strain that no longer produced any polycyclic triterpenoids. This strain was able to grow chemoheterotrophically, photoheterotrophically, and photoautotrophically, demonstrating that hopanoids are not required for growth under normal conditions. A severe growth defect, as well as significant morphological damage, was observed when cells were grown under acidic and alkaline conditions. Although minimal changes in
shc
transcript expression were observed under certain conditions of pH shock, the total amount of hopanoid production was unaffected; however, the abundance of methylated hopanoids significantly increased. This suggests that hopanoids may play an indirect role in pH homeostasis, with certain hopanoid derivatives being of particular importance.
Comparisons between Geographically Diverse Samples of Carried
Staphylococcus aureus
Authors: Ruimy Raymond , Armand-Lefevre Laurence , Barbier Francois , Ruppé Etienne , Cocojaru Radu , Mesli Yasmine , Maiga Aminata , Benkalfat Mokhtar , Benchouk Samia , Hassaine Hafida , Dufourcq Jean-Baptiste , Nareth Chhor , Sarthou Jean-Louis , Andremont Antoine , Feil Edward J. 
Published: July 2009

ABSTRACT

Approximately one-third of the human population is asymptomatically colonized by
Staphylococcus aureus
. However, much of the global diversity within the carriage populations remains uncharacterized, and it is unclear to what degree the variation is geographically partitioned. We isolated 300 carriage isolates from 1,531 adults contemporaneously in four countries: France, Algeria, Moldova, and Cambodia. All strains were characterized by multilocus sequence typing. Six clonal complexes (CCs) were present in all four samples (CC30, -45, -121, -15, -5, and -8). Analyses based on the genotype frequencies revealed the French and Algerian samples to be most similar and the Cambodian sample to be most distinct. While this pattern is consistent with likely rates of human migration and geographic distance, stochastic clonal expansion also contributes to regional differences. Phylogenetic analysis revealed a highly divergent and uncharacterized genotype (ST1223) within Cambodia. This lineage is related to CC75, which has previously been observed only in remote aboriginal populations in northern Australia.
Allelic Variation of Bile Salt Hydrolase Genes in
Lactobacillus salivarius
Does Not Determine Bile Resistance Levels
Authors: Fang Fang , Li Yin , Bumann Mario , Raftis Emma J. , Casey Pat G. , Cooney Jakki C. , Walsh Martin A. , O'Toole Paul W. 
Published: July 2009

ABSTRACT

Commensal lactobacilli frequently produce bile salt hydrolase (Bsh) enzymes whose roles in intestinal survival are unclear. Twenty-six
Lactobacillus salivarius
strains from different sources all harbored a
bsh1
allele on their respective megaplasmids. This allele was related to the plasmid-borne
bsh1
gene of the probiotic strain UCC118. A second locus (
bsh2
) was found in the chromosomes of two strains that had higher bile resistance levels. Four Bsh1-encoding allele groups were identified, defined by truncations or deletions involving a conserved residue. In vitro analyses showed that this allelic variation was correlated with widely varying bile deconjugation phenotypes. Despite very low activity of the UCC118 Bsh1 enzyme, a mutant lacking this protein had significantly lower bile resistance, both in vitro and during intestinal transit in mice. However, the overall bile resistance phenotype of this and other strains was independent of the
bsh1
allele type. Analysis of the
L. salivarius
transcriptome upon exposure to bile and cholate identified a multiplicity of stress response proteins and putative efflux proteins that appear to broadly compensate for, or mask, the effects of allelic variation of
bsh
genes. Bsh enzymes with different bile-degrading kinetics, though apparently not the primary determinants of bile resistance in
L. salivarius
, may have additional biological importance because of varying effects upon bile as a signaling molecule in the host.
TheMycobacterium tuberculosisSigma Factor σBIs Required for Full Response to Cell Envelope Stress and Hypoxia In Vitro, but It Is Dispensable for In Vivo Growth
Authors: Fontán P. A. , Voskuil M. I. , Gomez M. , Tan D. , Pardini M. , Manganelli R. , Fattorini L. , Schoolnik G. K. , Smith I. 
Published: July 2009

ABSTRACTThe numerous sigma (σ) factors present inMycobacterium tuberculosisare indicative of the adaptability of this pathogen to different environmental conditions. In this report, we describe theM. tuberculosisσBregulon and the phenotypes of anM. tuberculosis sigBmutant strain exposed to cell envelope stress, oxidative stress, and hypoxia. ThesigBmutant was especially defective in survival under hypoxic conditions in vitro, but it was not attenuated for growth in THP-1 cells or during mouse and guinea pig infection.
Pilin Antigenic Variation Occurs Independently of the RecBCD Pathway in
Neisseria gonorrhoeae
Authors: Helm R. Allen , Seifert H. Steven 
Published: July 2009

ABSTRACT

Type IV pilus expression has been strongly implicated in the virulence of
Neisseria gonorrhoeae
, the causative agent of gonorrhea. In
Neisseria
, these pili undergo frequent antigenic variation (Av), which is presumed to allow reinfection of high-risk groups. Pilin Av is the result of RecA-mediated recombination events between the gene encoding the major pilin subunit (
pilE
) and multiple silent pilin locus (
pilS
) copies, utilizing a RecF-like recombination pathway. The role of RecBCD in pilin Av has been controversial. Previous studies measuring pilin Av in
recB
and
recD
mutants in two independent strains of
N. gonorrhoeae
(MS11 and FA1090) by indirect methods yielded conflicting results. In addition, these two laboratory strains have been suggested to express very different DNA repair capabilities. We show that the FA1090 and MS11 parental strains have similar abilities to repair DNA damage via UV-induced DNA damage, nalidixic acid-induced double-strand breaks, and methyl methanesulfonate-induced alkylation and that RecB and RecD are involved in the repair of these lesions. To test the role of the RecBCD pathway in pilin Av, the rate and frequency of pilin Av were directly measured by sequencing the
pilE
locus in randomly selected piliated progeny of both MS11 and FA1090 in
recB
and
recD
mutants. Our results definitively show that
recB
and
recD
mutants undergo pilin Av at rates similar to those of the parents in both strain backgrounds, demonstrating that efficient pilin Av is neither enhanced nor inhibited by the RecBCD complex.
NtcA-Regulated Heterocyst Differentiation Genes
hetC
and
devB
from
Anabaena
sp. Strain PCC 7120 Exhibit a Similar Tandem Promoter Arrangement
Authors: Muro-Pastor Alicia M. , Flores Enrique , Herrero Antonia 
Published: July 2009

ABSTRACT

Transcription of the
hetC
gene, whose product is required for heterocyst differentiation, takes place from a long promoter region that includes the previously described HetR-independent, NtcA-activated promoter producing transcripts with a 5′ end corresponding to position −571 with respect to the translational start site of
hetC
. Northern blot analysis indicated that the accumulation of
hetC
transcripts depends on HetR, and a second transcriptional start site located at position −293 that leads to NtcA-dependent, HetR-dependent inducible transcription of
hetC
was identified. Upon nitrogen stepdown, expression of a P

hetC

::
gfp
fusion was transiently induced in specific cells that were differentiating into heterocysts, both when the whole promoter region (containing transcription start points −571 and −293) or a short version (containing only the transcription start point −293) was used. Expression of
hetC
from the −293 position was delayed in a strain bearing a deleted promoter region lacking sequences upstream from position −570. Such a strain was still able to differentiate functional heterocysts and to grow diazotrophically, although diazotrophic growth was impaired under certain conditions. Similarly, a second, NtcA-dependent, HetR-dependent transcriptional start site was identified at position −454 in the promoter region upstream from the
devBCA
operon encoding an ABC transport system involved in heterocyst maturation, in which an NtcA-dependent promoter producing transcripts starting at position −704 had been previously noted. Thus, the
hetC
and
devBCA
promoter regions exhibit similar tandem promoter arrangements.
Acyl Enzyme Intermediates in Sortase-Catalyzed Pilus Morphogenesis in Gram-Positive Bacteria
Authors: Guttilla Irene K. , Gaspar Andrew H. , Swierczynski Arlene , Swaminathan Anu , Dwivedi Prabhat , Das Asis , Ton-That Hung 
Published: July 2009

ABSTRACT

In gram-positive bacteria, covalently linked pilus polymers are assembled by a specific transpeptidase enzyme called pilus-specific sortase. This sortase is postulated to cleave the LPXTG motif of a pilin precursor between threonine and glycine and to form an acyl enzyme intermediate with the substrate. Pilus polymerization is believed to occur through the resolution of this intermediate upon specific nucleophilic attack by the conserved lysine located within the pilin motif of another pilin monomer, which joins two pilins with an isopeptide bond formed between threonine and lysine. Here, we present evidence for sortase reaction intermediates in
Corynebacterium diphtheriae
. We show that truncated SrtA mutants that are loosely bound to the cytoplasmic membrane form high-molecular-weight complexes with SpaA polymers secreted into the extracellular milieu. These complexes are not formed with SpaA pilin mutants that have alanine substitutions in place of threonine in the LPXTG motif or lysine in the pilin motif. The same phenotype is observed with alanine substitutions of either the conserved cysteine or histidine residue of SrtA known to be required for catalysis. Remarkably, the assembly of SpaA pili, or the formation of intermediates, is abolished with a SrtA mutant missing the membrane-anchoring domain. We infer that pilus polymerization involves the formation of covalent pilin-sortase intermediates, which occurs within a molecular platform on the exoplasmic face of the cytoplasmic membrane that brings together both sortase and its cognate substrates in close proximity to each other, likely surrounding a secretion apparatus. We present electron microscopic data in support of this picture.