bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rhizonin, the First Mycotoxin Isolated from the Zygomycota, Is Not a Fungal Metabolite but Is Produced by Bacterial Endosymbionts
Authors: Partida-Martinez Laila P. , Flores de Looß Carina , Ishida Keishi , Ishida Mie , Roth Martin , Buder Katrin , Hertweck Christian 
Published: November 2006

ABSTRACT

Rhizonin is a hepatotoxic cyclopeptide isolated from cultures of a fungal
Rhizopus microsporus
strain that grew on moldy ground nuts in Mozambique. Reinvestigation of this fungal strain by a series of experiments unequivocally revealed that this “first mycotoxin from lower fungi” is actually not produced by the fungus. PCR experiments and phylogenetic studies based on 16S rRNA gene sequences revealed that the fungus is associated with bacteria belonging to the genus
Burkholderia
. By transmission electron microscopy, the bacteria were localized within the fungal cytosol. Toxin production and the presence of the endosymbionts were correlated by curing the fungus with an antibiotic, yielding a nonproducing, symbiont-free phenotype. The final evidence for a bacterial biogenesis of the toxin was obtained by the successful fermentation of the endosymbiotic bacteria in pure culture and isolation of rhizonin A from the broth. This finding is of particular interest since
Rhizopus microsporus
and related
Rhizopus
species are frequently used in food preparations such as tempeh and sufu.
Exopolysaccharide Expression in
Lactococcus lactis
subsp.
cremoris
Ropy352: Evidence for Novel Gene Organization
Authors: Knoshaug Eric P. , Ahlgren Jeff A. , Trempy Janine E. 
Published: November 2006

ABSTRACT

Lactococcus lactis
subsp.
cremoris
Ropy352 produces two distinct heteropolysaccharides, phenotypically described as ropy and mucoid, when cultured in nonfat milk. One exopolysaccharide precipitated with 50% ethanol as a series of elongated threads and was composed of glucose and galactose in a molar ratio of 3:2. The second exopolysaccharide precipitated with 75% ethanol as a fine flocculant and consisted of galactose, glucose, and mannose with a molar ratio of 67:21:12. A mutant strain,
L. lactis
subsp.
cremoris
EK240, lacking the ropy phenotype did not produce the exopolysaccharide that precipitated with 50% ethanol; however, it produced the exopolysaccharide that precipitated with 75% ethanol, indicating that the former exopolysaccharide is essential for the ropy phenotype. Cultures of
L. lactis
subsp.
cremoris
Ropy352 in 10% nonfat milk reached a viscosity of 25 Pa-s after 24 h, while those of the nonropy
L. lactis
subsp.
cremoris
EK240 mutant did not change. A mutation abolishing ropy exopolysaccharide expression mapped to a region on a plasmid containing two open reading frames,
epsM
and
epsN
, encoding novel glycosyltransferases bordered by IS
S1
elements oriented in the same direction. Sequencing of this plasmid revealed two other regions involved in exopolysaccharide expression, an operon located between partial IS
981
and IS
982
elements, and an independent gene,
epsU
. Two and possibly three of these regions are involved in
L. lactis
subsp.
cremoris
Ropy352 exopolysaccharide expression and are arranged in a novel fashion different from that of typical lactococcal exopolysaccharide loci, and this provides genetic evidence for exopolysaccharide gene reorganization and evolution in
Lactococcus
.
Characterization of Chimeric
Bacillus thuringiensis
Vip3 Toxins
Authors: Fang Jun , Xu Xiaoli , Wang Ping , Zhao Jian-Zhou , Shelton Anthony M. , Cheng Jiaan , Feng Ming-Guang , Shen Zhicheng 
Published: November 2006

ABSTRACT

Bacillus thuringiensis
vegetative insecticidal proteins (Vip) are potential alternatives for
B. thuringiensis
endotoxins that are currently utilized in commercial transgenic insect-resistant crops. Screening a large number of
B. thuringiensis
isolates resulted in the cloning of
vip3Ac1
. Vip3Ac1 showed high insecticidal activity against the fall armyworm
Spodoptera frugiperda
and the cotton bollworm
Helicoverpa zea
but very low activity against the silkworm
Bombyx mori
. The host specificity of this Vip3 toxin was altered by sequence swapping with a previously identified toxin, Vip3Aa1. While both Vip3Aa1 and Vip3Ac1 showed no detectable toxicity against the European corn borer
Ostrinia nubilalis
, the chimeric protein Vip3AcAa, consisting of the N-terminal region of Vip3Ac1 and the C-terminal region of Vip3Aa1, became insecticidal to the European corn borer. In addition, the chimeric Vip3AcAa had increased toxicity to the fall armyworm. Furthermore, both Vip3Ac1 and Vip3AcAa are highly insecticidal to a strain of cabbage looper (
Trichoplusia ni
) that is highly resistant to the
B. thuringiensis
endotoxin Cry1Ac, thus experimentally showing for the first time the lack of cross-resistance between
B. thuringiensis
Cry1A proteins and Vip3A toxins. The results in this study demonstrated that
vip3Ac1
and its chimeric
vip3
genes can be excellent candidates for engineering a new generation of transgenic plants for insect pest control.
Preparation of Monoclonal Antibodies for Detection and Identification of
Francisella tularensis
Authors: Hotta Akitoyo , Uda Akihiko , Fujita Osamu , Tanabayashi Kiyoshi , Yamada Akio 
Published: November 2006

ABSTRACT

Monoclonal antibodies (MAbs) against
Francisella tularensis
were obtained. Three MAbs specifically reacted with
F. tularensis
, while four MAbs reacted with other members of the genus
Francisella
as well. Fluorescent isothiocyanate-conjugated MAbs unequivocally stained bacterial cells in specimens from experimentally infected mice. Two MAbs agglutinated
F. tularensis
antigen in the agglutination tests. These MAbs should improve methods for detection and identification of
F. tularensis
.
Limited Functional Redundancy and Oscillation of Cyclins in Multinucleated
Ashbya gossypii
Fungal Cells
Authors: Hungerbuehler A. Katrin , Philippsen Peter , Gladfelter Amy S. 
Published: November 2006

ABSTRACT

Cyclin protein behavior has not been systematically investigated in multinucleated cells with asynchronous mitoses. Cyclins are canonical oscillating cell cycle proteins, but it is unclear how fluctuating protein gradients can be established in multinucleated cells where nuclei in different stages of the division cycle share the cytoplasm. Previous work in
A. gossypii
, a filamentous fungus in which nuclei divide asynchronously in a common cytoplasm, demonstrated that one G1 and one B-type cyclin do not fluctuate in abundance across the division cycle. We have undertaken a comprehensive analysis of all G1 and B-type cyclins in
A. gossypii
to determine whether any of the cyclins show periodic abundance across the cell cycle and to examine whether cyclins exhibit functional redundancy in such a cellular environment. We localized all G1 and B-type cyclins and notably found that only AgClb5/6p varies in subcellular localization during the division cycle. AgClb5/6p is lost from nuclei at the meta-anaphase transition in a D-box-dependent manner. These data demonstrate that efficient nuclear autonomous protein degradation can occur within multinucleated cells residing in a common cytoplasm. We have shown that three of the five cyclins in
A. gossypii
are essential genes, indicating that there is minimal functional redundancy in this multinucleated system. In addition, we have identified a cyclin, AgClb3/4p, that is essential only for sporulation. We propose that the cohabitation of different cyclins in nuclei has led to enhanced substrate specificity and limited functional redundancy within classes of cyclins in multinucleated cells.
Phosphoinositides Are Involved in Control of the Glucose-Dependent Growth Resumption That Follows the Transition Phase inStreptomyces lividans
Authors: Chouayekh H. , Nothaft H. , Delaunay S. , Linder M. , Payrastre B. , Seghezzi N. , Titgemeyer F. , Virolle M. J. 
Published: November 2006

ABSTRACTThe interruption of thesblAgene ofStreptomyces lividanswas previously shown to lead to relief of glucose repression of the normally strongly glucose-repressed α-amylase gene. In addition to this relief, an early entry into stationary phase was observed when cells were grown in a minimal medium containing glucose as the main carbon source. In this study, we established that this mutant does not resume growth after the transition phase when cultured in the complex glucose-rich liquid medium R2YE and sporulates much earlier than the wild-type strain when plated on solid R2YE. These phenotypic differences, which were abolished when glucose was omitted from the R2YE medium, correlated with a reduced glucose uptake ability of thesblAmutant strain.sblAwas shown to encode a bifunctional enzyme possessing phospholipase C-like and phosphoinositide phosphatase activities. The cleavage of phosphoinositides by SblA seems necessary to trigger the glucose-dependent renewed growth that follows the transition phase. The transient expression ofsblAthat takes place just before the transition phase is consistent with a regulatory role for this gene during the late stages of growth. The tight temporal control ofsblAexpression was shown to depend on two operator sites. One, located just upstream of the −35 promoter region, likely constitutes a repressor binding site. The other, located 170 bp downstream of the GTGsblAtranslational start codon, may be involved in the regulation of the degradation of thesblAtranscript. This study suggests that phosphoinositides constitute important regulatory molecules inStreptomyces, as they do in eukaryotes.
Crystal Structure of Uroporphyrinogen Decarboxylase fromBacillus subtilis
Authors: Fan Jun , Liu Qun , Hao Quan , Teng Maikun , Niu Liwen 
Published: November 2006

ABSTRACTUroporphyrinogen decarboxylase (UROD) is a branch point enzyme in the biosynthesis of the tetrapyrroles. It catalyzes the decarboxylation of four acetate groups of uroporphyrinogen III to yield coproporphyrinogen III, leading to heme and chlorophyll biosynthesis. UROD is a special type of nonoxidative decarboxylase, since no cofactor is essential for catalysis. In this work, the first crystal structure of a bacterial UROD,Bacillus subtilisUROD (URODBs), has been determined at a 2.3 Å resolution. The biological unit of URODBswas determined by dynamic light scattering measurements to be a homodimer in solution. There are four molecules in the crystallographic asymmetric unit, corresponding to two homodimers. Structural comparison of URODBswith eukaryotic URODs reveals a variation of two loops, which possibly affect the binding of substrates and release of products. Structural comparison with the human UROD-coproporphyrinogen III complex discloses a similar active cleft, with five invariant polar residues (Arg29, Arg33, Asp78, Tyr154, and His322) and three invariant hydrophobic residues (Ile79, Phe144, and Phe207), in URODBs. Among them, Asp78 may interact with the pyrrole NH groups of the substrate, and Arg29 is a candidate for positioning the acetate groups of the substrate. Both residues may also play catalytic roles.
Identification of Genes Regulated by the
cepIR
Quorum-Sensing System in
Burkholderia cenocepacia
by High-Throughput Screening of a Random Promoter Library
Authors: Subsin Benchamas , Chambers Catherine E. , Visser Michelle B. , Sokol Pamela A. 
Published: November 2006

ABSTRACT

The
Burkholderia cenocepacia cepIR
quorum-sensing system regulates expression of extracellular proteases, chitinase, and genes involved in ornibactin biosynthesis, biofilm formation, and motility. In a genome-wide screen we identified
cepIR
-regulated genes by screening a random promoter library of
B. cenocepacia
K56-2 constructed in a luminescence reporter detection plasmid for differential expression in response to
N
-octanoyl-
l
-homoserine lactone (OHL). Eighty-nine clones were identified; in 58 of these clones expression was positively regulated by
cepIR
, and in 31 expression was negatively regulated by
cepIR
. The expression profiles of the 89 promoter clones were compared in the
cepI
mutant K56-dI2 in medium supplemented with 30 pM OHL and K56-2 to confirm that the presence of OHL restored expression to wild-type levels. To validate the promoter library observations and to determine the effect of a
cepR
mutation on expression of selected genes, the mRNA levels of nine genes whose promoters were predicted to be regulated by
cepR
were quantitated by quantitative reverse transcription-PCR in the wild type and
cepI
and
cepR
mutants. The expression levels of all nine genes were similar in the
cepI
and
cepR
mutants and consistent with the promoter-
lux
reporter activity. The expression of four selected
cepIR
-regulated gene promoters was examined in a
cciIR
mutant, and two of these promoters were also regulated by
cciIR
. This study extends our understanding of genes whose expression is influenced by
cepIR
and indicates the global regulatory effect of the
cepIR
system in
B. cenocepacia
.
Analysis of Storage Lipid Accumulation in
Alcanivorax borkumensis
: Evidence for Alternative Triacylglycerol Biosynthesis Routes in Bacteria
Authors: Kalscheuer Rainer , Stöveken Tim , Malkus Ursula , Reichelt Rudolf , Golyshin Peter N. , Sabirova Julia S. , Ferrer Manuel , Timmis Kenneth N. , Steinbüchel Alexander 
Published: November 2006

ABSTRACT

Marine hydrocarbonoclastic bacteria, like
Alcanivorax borkumensis
, play a globally important role in bioremediation of petroleum oil contamination in marine ecosystems. Accumulation of storage lipids, serving as endogenous carbon and energy sources during starvation periods, might be a potential adaptation mechanism for coping with nutrient limitation, which is a frequent stress factor challenging those bacteria in their natural marine habitats. Here we report on the analysis of storage lipid biosynthesis in
A. borkumensis
strain SK2. Triacylglycerols (TAGs) and wax esters (WEs), but not poly(hydroxyalkanoic acids), are the principal storage lipids present in this and other hydrocarbonoclastic bacterial species. Although so far assumed to be a characteristic restricted to gram-positive actinomycetes, substantial accumulation of TAGs corresponding to a fatty acid content of more than 23% of the cellular dry weight is the first characteristic of large-scale de novo TAG biosynthesis in a gram-negative bacterium. The acyltransferase AtfA1 (ABO_2742) exhibiting wax ester synthase/acyl-coenzyme A:diacylglycerol acyltransferase (WS/DGAT) activity plays a key role in both TAG and WE biosynthesis, whereas AtfA2 (ABO_1804) was dispensable for storage lipid formation. However, reduced but still substantial residual TAG levels in
atfA1
and
atfA2
knockout mutants compellingly indicate the existence of a yet unknown WS/DGAT-independent alternative TAG biosynthesis route. Storage lipids of
A. borkumensis
were enriched in saturated fatty acids and accumulated as insoluble intracytoplasmic inclusions exhibiting great structural variety. Storage lipid accumulation provided only a slight growth advantage during short-term starvation periods but was not required for maintaining viability and long-term persistence during extended starvation phases.
Genome-Wide Screening of Genes Required for Swarming Motility inEscherichia coliK-12
Authors: Inoue Tetsuyoshi , Shingaki Ryuji , Hirose Shotaro , Waki Kaori , Mori Hirotada , Fukui Kazuhiro 
Published: November 2006

ABSTRACTEscherichia coliK-12 has the ability to migrate on semisolid media by means of swarming motility. A systematic and comprehensive collection of gene-disruptedE. coliK-12 mutants (the Keio collection) was used to identify the genes involved in the swarming motility of this bacterium. Of the 3,985 nonessential gene mutants, 294 were found to exhibit a strongly repressed-swarming phenotype. Further, 216 of the 294 mutants displayed no significant defects in swimming motility; therefore, the 216 genes were considered to be specifically associated with the swarming phenotype. The swarming-associated genes were classified into various functional categories, indicating that swarming is a specialized form of motility that requires a wide variety of cellular activities. These genes include genes for tricarboxylic acid cycle and glucose metabolism, iron acquisition, chaperones and protein-folding catalysts, signal transduction, and biosynthesis of cell surface components, such as lipopolysaccharide, the enterobacterial common antigen, and type 1 fimbriae. Lipopolysaccharide and the enterobacterial common antigen may be important surface-acting components that contribute to the reduction of surface tension, thereby facilitating the swarm migration in theE. coliK-12 strain.
Involvement of the
cynABDS
Operon and the CO
2
-Concentrating Mechanism in the Light-Dependent Transport and Metabolism of Cyanate by Cyanobacteria
Authors: Espie George S. , Jalali Farid , Tong Tommy , Zacal Natalie J. , So Anthony K.-C. 
Published: November 2006

ABSTRACT

The cyanobacteria
Synechococcus elongatus
strain PCC7942 and
Synechococcus
sp. strain UTEX625 decomposed exogenously supplied cyanate (NCO
−
) to CO
2
and NH
3
through the action of a cytosolic cyanase which required HCO
3
−
as a second substrate. The ability to metabolize NCO
−
relied on three essential elements: proteins encoded by the
cynABDS
operon, the biophysical activity of the CO
2
-concentrating mechanism (CCM), and light. Inactivation of
cynS
, encoding cyanase, and
cynA
yielded mutants unable to decompose cyanate. Furthermore, loss of CynA, the periplasmic binding protein of a multicomponent ABC-type transporter, resulted in loss of active cyanate transport. Competition experiments revealed that native transport systems for CO
2
, HCO
3
−
, NO
3
−
, NO
2
−
, Cl
−
, PO
4
2−
, and SO
4
2−
did not contribute to the cellular flux of NCO
−
and that CynABD did not contribute to the flux of these nutrients, implicating CynABD as a novel primary active NCO
−
transporter. In the
S. elongatus
strain PCC7942 Δ
chpX
Δ
chpY
mutant that is defective in the full expression of the CCM, mass spectrometry revealed that the cellular rate of cyanate decomposition depended upon the size of the internal inorganic carbon (C
i
) (HCO
3
−
+ CO
2
) pool. Unlike wild-type cells, the rate of NCO
−
decomposition by the Δ
chpX
Δ
chpY
mutant was severely depressed at low external C
i
concentrations, indicating that the CCM was essential in providing HCO
3
−
for cyanase under typical growth conditions. Light was required to activate and/or energize the active transport of both NCO
−
and C
i
. Putative
cynABDS
operons were identified in the genomes of diverse
Proteobacteria
, suggesting that CynABDS-mediated cyanate metabolism is not restricted to cyanobacteria.
The Inner Cavity ofEscherichia coliDegP Protein Is Not Essentialfor Molecular Chaperone and Proteolytic Activity
Authors: Jomaa Ahmad , Damjanovic Daniela , Leong Vivian , Ghirlando Rodolfo , Iwanczyk Jack , Ortega Joaquin 
Published: November 2006

ABSTRACTTheEscherichia coliDegP protein is an essential periplasmic protein for bacterial survival at high temperatures. DegP has the unusual property of working as a chaperone below 28°C, but efficiently degrading unfolded proteins above 28°C. Monomeric DegP contains a protease domain and two PDZ domains. It oligomerizes into a hexameric cage through the staggered association of trimers. The active sites are located in a central cavity that is only accessible laterally, and the 12 PDZ domains act as mobile sidewalls that mediate opening and closing of the gates. As access to the active sites is restricted, DegP is an example of a self-compartmentalized protease. To determine the essential elements of DegP that maintain the integrity of the hexameric cage, we constructed several deletion mutants of DegP that formed trimers rather than hexamers. We found that residues 39 to 78 within the LA loops, as well as the PDZ2 domains are essential for the integrity of the DegP hexamer. In addition, we asked whether an enclosed cavity or cage of specific dimensions is required for the protease and chaperone activities in DegP. Both activities were maintained in the trimeric DegP mutants without an enclosed cavity and in deletion DegP mutants with significantly reduced dimensions of the cage. We conclude that the functional unit for the protease and chaperone activities of DegP is a trimer and that neither a cavity of specific dimensions nor the presence of an enclosed cavity appears to be essential for the protease and chaperone activities of DegP.
Regulation of Denitrification Genes in
Neisseria meningitidis
by Nitric Oxide and the Repressor NsrR
Authors: Rock Jonathan D. , Thomson Melanie J. , Read Robert C. , Moir James W. B. 
Published: November 2006

ABSTRACT

The human pathogen
Neisseria meningitidis
is capable of growth using the denitrification of nitrite to nitrous oxide under microaerobic conditions. This process is catalyzed by two reductases: nitrite reductase (encoded by
aniA
) and nitric oxide (NO) reductase (encoded by
norB
). Here, we show that in
N. meningitidis
MC58
norB
is regulated by nitric oxide via the product of gene NMB0437 which encodes NsrR. NsrR is a repressor in the absence of NO, but
norB
expression is derepressed by NO in an NsrR-dependent manner.
nsrR
-deficient mutants grow by denitrification more rapidly than wild-type
N. meningitidis
, and this is coincident with the upregulation of both NO reductase and nitrite reductase even under aerobic conditions in the absence of nitrite or NO. The NsrR-dependent repression of
aniA
(unlike that of
norB
) is not lifted in the presence of NO. The role of NsrR in the control of expression of
aniA
is linked to the function of the anaerobic activator protein FNR: analysis of
nsrR
and
fnr
single and
nsrR fnr
double mutants carrying an
aniA
promoter
lacZ
fusion indicates that the role of NsrR is to prevent FNR-dependent
aniA
expression under aerobic conditions, indicating that FNR in
N. meningitidis
retains considerable activity aerobically.
Membrane-Spanning and Periplasmic Segments of CcmI Have Distinct Functions during Cytochrome
c
Biogenesis in
Rhodobacter capsulatus
Authors: Sanders Carsten , Boulay Clémence , Daldal Fevzi 
Published: November 2006

ABSTRACT

In gram-negative bacteria, like
Rhodobacter capsulatus
, about 10 membrane-bound components (CcmABCDEFGHI and CcdA) are required for periplasmic maturation of
c
-type cytochromes. These components perform the chaperoning and thio-oxidoreduction of the apoproteins as well as the delivery and ligation of the heme cofactors. In the absence of any of these components, including CcmI, proposed to act as an apocytochrome
c
chaperone,
R. capsulatus
does not have the ability to produce holocytochromes
c
or consequently to exhibit photosynthetic growth and cytochrome
cbb
3
oxidase activity. Previously, we have demonstrated that null mutants of CcmI partially overcome cytochrome
c
deficiency phenotypes upon overproduction of the CcmF-
R. capsulatus
CcmH (CcmF-CcmH
Rc
) couple in a growth medium-dependent manner and fully bypass these defects by additional overproduction of CcmG. Here, we show that overproduction of the CcmF-CcmH
Rc
couple and overproduction of the N-terminal membrane-spanning segment of CcmI (CcmI-1) have similar suppression effects of cytochrome
c
maturation defects in CcmI-null mutants. Likewise, additional overproduction of CcmG, the C-terminal periplasmic segment of CcmI (CcmI-2), or even of apocytochrome
c
2
also provides complementation abilities similar to those of these mutants. These results indicate that the two segments of CcmI have different functions and support our earlier findings that two independent steps are required for full recovery of the loss of CcmI function. We therefore propose that CcmI-1 is part of the CcmF-CcmH
Rc
-dependent heme ligation, while CcmI-2 is involved in the CcdA- and CcmG-dependent apoprotein thioreduction steps, which intersect at the level of CcmI during cytochrome
c
biogenesis.