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The Bacillus subtilis Extracytoplasmic-Function X Factor Regulates Modification of the Cell Envelope and Resistance to Cationic Antimicrobial Peptides. Min Cao, 2004. Bacillus subtilis contains seven extracytoplasmic-function 
factors that activate partially overlapping regulons . We here
identify four additional members of the
X
regulon, pbpX [penicillin-bindingprotein], ywnJ, the
dlt operon [D-alanylation of teichoic acids],
and the pss ybfM psd operon [phosphatidylethanolamine
biosynthesis].Modification of teichoic acids by esterification with
D-alanineand incorporation of
phosphatidylethanolamine into the cellmembrane have a common
consequence: in both cases positivelycharged amino groups are
introduced into the cell envelope.The resulting reduction in the net
negative charge of the cellenvelope has been previously implicated
as a resistance mechanismspecific for cationic antimicrobial
peptides . Consistent withthis notion, we find that both sigX
and dltA mutants are moresensitive to nisin than wild-type
cells . We conclude that activationof the
X
regulon serves to alter cell surface properties toprovide protection
against antimicrobial peptides.HutZ Is Required for Efficient Heme Utilization in Vibrio cholerae. Elizabeth E. Wyckoff, 2004.Vibrio cholerae, the causative agent of cholera, requires iron for growth . One mechanism by which it acquires iron is the uptake of heme, and several heme utilization genes have been identified in V . cholerae . These include three distinct outer membrane receptors, two TonB systems, and an apparent ABC transporter to transfer heme across the inner membrane . However, little is known about the fate of the heme after it enters the cell . In this report we show that a novel heme utilization protein, HutZ, is required for optimal heme utilization . hutZ (open reading frame [ORF] VCA0907) is encoded with two other genes, hutW (ORF VCA0909) and hutX (ORF VCA0908), in an operon divergently transcribed from the tonB1 operon . A hutZ mutant grew poorly when heme was provided as the sole source of iron, and the poor growth was likely due to the failure to use heme efficiently as a source of iron, rather than to heme toxicity . Heme oxygenase mutants of both Corynebacterium diphtheriae and C . ulcerans fail to use heme as an iron source . When the hutWXZ genes were expressed in the heme oxygenase mutants, growth on heme was restored, and hutZ was required for this effect . Biochemical characterization indicated that HutZ binds heme with high efficiency; however, no heme oxygenase activity was detected for this protein . HutZ may act as a heme storage protein, and it may also function as a shuttle protein that increases the efficiency of heme trafficking from the membrane to heme-containing proteins . Differential Expression of the CO2 Fixation Operons of Rhodobacter sphaeroides by the Prr/Reg Two-Component System during Chemoautotrophic Growth. Janet L. Gibson, 2002.In Rhodobacter sphaeroides, the two cbb operons encoding duplicated Calvin-Benson Bassham (CBB) CO2 fixation reductive pentose phosphate cycle structural genes are differentially controlled . In attempts to define the molecular basis for the differential regulation, the effects of mutations in genes encoding a subunit of Cbb3 cytochrome oxidase, ccoP, and a global response regulator, prrA (regA), were characterized with respect to CO2 fixation (cbb) gene expression by using translational lac fusions to the R . sphaeroides cbbI and cbbII promoters . Inactivation of the ccoP gene resulted in derepression of both promoters during chemoheterotophic growth, where cbb expression is normally repressed; expression was also enhanced over normal levels during phototrophic growth . The prrA mutation effected reduced expression of cbbI and cbbII promoters during chemoheterotrophic growth, whereas intermediate levels of expression were observed in a double ccoP prrA mutant . PrrA and ccoP1 prrA strains cannot grow phototrophically, so it is impossible to examine cbb expression in these backgrounds under this growth mode . In this study, however, we found that PrrA mutants of R . sphaeroides were capable of chemoautotrophic growth, allowing, for the first time, an opportunity to directly examine the requirement of PrrA for cbb gene expression in vivo under growth conditions where the CBB cycle and CO2 fixation are required . Expression from the cbbII promoter was severely reduced in the PrrA mutants during chemoautotrophic growth, whereas cbbI expression was either unaffected or enhanced . Mutations in ccoQ had no effect on expression from either promoter . These observations suggest that the Prr signal transduction pathway is not always directly linked to Cbb3 cytochrome oxidase activity, at least with respect to cbb gene expression . In addition, lac fusions containing various lengths of the cbbI promoter demonstrated distinct sequences involved in positive regulation during photoautotrophic versus chemoautotrophic growth, suggesting that different regulatory proteins may be involved . In Rhodobacter capsulatus, ribulose 1,5-bisphosphate carboxylase-oxygenase (RubisCO) expression was not affected by cco mutations during photoheterotrophic growth, suggesting that differences exist in signal transduction pathways regulating cbb genes in the related organisms . Effect of Raw-Milk Cheese Consumption on the Enterococcal Flora of Human Feces. Roberto Gelsomino, 2003.Enterococci are one of the major facultative anaerobic bacterial groups that reside in the human gastrointestinal tract . In the present study, the composition of the enterococcal fecal flora in three healthy humans was analyzed before, during, and after the daily consumption of  125 g of a raw-milk Cheddar-type cheese containing 3.2 x 104 enterococci/g of cheese . Enterococcal counts ranged between 1.4 x 102 and 2.5 x 108 CFU/g of feces and differed from subject to subject and from week to week . The cheese contained mainly Enterococcus casseliflavus and a small population of Enterococcus faecalis . Clonal relationships were determined by pulsed-field gel electrophoresis . Before and after consumption of the cheese, samples from humans contained mainly Enterococcus faecium, with some of the clones being resident . During consumption of the cheese, one particular transient clone of E . faecalis, clone Fs2, which was present in small numbers in the cheese, largely dominated the feces . Two clones of E . casseliflavus from the cheese were also found in the feces of one of the subjects during cheese consumption . These results suggest that a clone need not be present in a food in high numbers to establish itself in the intestine .
CodY-Regulated Aminotransferases AraT and BcaT Play a Major Role in the Growth of Lactococcus lactis in Milk by Regulating the Intracellular Pool of Amino Acids. Emilie Chambellon, 2003.Aminotransferases, which catalyze the last step of biosynthesis of most amino acids and the first step of their catabolism, may be involved in the growth of Lactococcus lactis in milk . Previously, we isolated two aminotransferases from L . lactis, AraT and BcaT, which are responsible for the transamination of aromatic amino acids, branched-chain amino acids, and methionine . In this study, we demonstrated that double inactivation of AraT and BcaT strongly reduced the growth of L . lactis in milk . Supplementation of milk with amino acids and keto acids that are substrates of both aminotransferases did not improve the growth of the double mutant . On the contrary, supplementation of milk with isoleucine or a dipeptide containing isoleucine almost totally inhibited the growth of the double mutant, while it did not affect or only slightly affected the growth of the wild-type strain . These results suggest that AraT and BcaT play a major role in the growth of L . lactis in milk by degrading the intracellular excess isoleucine, which is responsible for the growth inhibition . The growth inhibition by isoleucine is likely to be due to CodY repression of the proteolytic system, which is necessary for maximal growth of L . lactis in milk, since the growth of the CodY mutant was not affected by addition of isoleucine to milk . Moreover, we demonstrated that AraT and BcaT are part of the CodY regulon and therefore are regulated by nutritional factors, such as the carbohydrate and nitrogen sources .
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