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Ecological Significance of Microdiversity: Identical 16S rRNA Gene Sequences Can Be Found in Bacteria with Highly Divergent Genomes and Ecophysiologies. Elke Jaspers, 2004.A combination of cultivation-based methods with a molecular biological approach was used to investigate whether planktonic bacteria with identical 16S rRNA gene sequences can represent distinct eco- and genotypes . A set of 11 strains of Brevundimonas alba were isolated from a bacterial freshwater community by conventional plating or by using a liquid most-probable-number (MPN) dilution series . These strains had identical 16S rRNA gene sequences and represented the dominant phylotype in the plateable fraction, as well as in the highest positive dilutions of the MPN series . However, internally transcribed spacer and enterobacterial repetitive intergenic consensus PCR fingerprinting analyses, as well as DNA-DNA hybridization analyses, revealed great genetic diversity among the 11 strains . Each strain utilized a specific combination of 59 carbon substrates, and the niche overlap indices were low, suggesting that each strain occupied a different ecological niche . In dialysis cultures incubated in situ, each strain had a different growth rate and cell yield . We thus demonstrated that the B . alba strains represent distinct populations with genetically determined adaptations and probably occupy different ecological niches . Our results have implications for assessment of the diversity and biogeography of bacteria and increase the perception of natural diversity beyond the level of 16S rRNA gene sequences . Mutation in the relA Gene of Vibrio cholerae Affects In Vitro and In Vivo Expression of Virulence Factors. Shruti Haralalka, 2003.The relA gene product determines the level of (p)ppGpp, the effector nucleotides of the bacterial stringent response that are also involved in the regulation of other functions, like antibiotic production and quorum sensing . In order to explore the possible involvement of relA in the regulation of virulence of Vibrio cholerae, a relA homolog from the organism (relAVCH) was cloned and sequenced . The relAVCH gene encodes a 738-amino-acid protein having functions similar to those of other gram-negative bacteria, including Escherichia coli . A  relA::kan allele was generated by replacing
 31% of the open reading frame of wild-type relA of V . cholerae El Tor strain C6709 with a kanamycin resistance gene . The V . cholerae relA mutant strain thus generated, SHK17, failed to accumulate (p)ppGpp upon amino acid deprivation . Interestingly, compared to the wild type, C6709, the mutant strain SHK17 exhibited significantly reduced in vitro production of two principal virulence factors, cholera toxin (CT) and toxin-coregulated pilus (TCP), under virulence gene-inducing conditions . In vivo experiments carried out in rabbit ileal loop and suckling mouse models also confirmed our in vitro results . The data suggest that (p)ppGpp is essential for maximal expression of CT and TCP during in vitro growth, as well as during intestinal infection by virulent V . cholerae . Northern blot and reverse transcriptase PCR analyses indicated significant reduction in the transcript levels of both virulence factors in the relA mutant strain SHK17 . Such marked alteration of virulence phenotypes in SHK17 appears most likely to be due to down regulation of transcript levels of toxR and toxT, the two most important virulence regulatory genes of V . cholerae. In SHK17, the altered expression of the two outer membrane porin proteins, OmpU and OmpT, indicated that the relA mutation most likely affects the ToxR-dependent virulence regulatory pathway, because it had been shown earlier that ToxR directly regulates their expression independently of ToxT .
Microbial Reduction and Precipitation of Vanadium by Shewanella oneidensis. W. Carpentier, 2003.Shewanella oneidensis couples anaerobic oxidation of lactate, formate, and pyruvate to the reduction of vanadium pentoxide (VV) . The bacterium reduces VV (vanadate ion) to VIV (vanadyl ion) in an anaerobic atmosphere . The resulting vanadyl ion precipitates as a VIV-containing solid .
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