Global changes in gene expression observed at the transition from growth to stationary phase in Listeria monocytogenes ScottA batch culture

Listeria monocytogenes is a food-borne Gram-positive bacterium that is responsible for a variety of infections (worldwide) annually. The organism is able to survive a variety of environmental conditions and stresses, however, the mechanisms by which L. monocytogenes adapts to environmental change are yet to be fully elucidated. An understanding of the mechanism(s) by which L. monocytogenes survives unfavourable environmental conditions will aid in developing new food processing methods to control the organism in foodstuffs. We have utilized a proteomic approach to investigate the response of L. monocytogenes batch cultures to the transition from exponential to stationary growth phase. Proteomic analysis showed that batch cultures of L. monocytogenes perceived stress and began preparations for stationary phase much earlier (approximately A(600) = 0.75, mid-exponential) than predicted by growth characteristics alone. Global analysis of the proteome revealed that the expression levels of more than 50% of all proteins observed changed significantly over a 7-9 h period during this transition phase. We have highlighted ten proteins in particular whose expression levels appear to be important in the early onset of the stationary phase. The significance of these findings in terms of functionality and the mechanistic picture are discussed.

The detection of environmental autoinducing peptide quorum-sensing genes from an uncultured Clostridium sp in landfill leachate reactor biomass

Aims: To elucidate whether a dominant uncultured clostridial (Clostridium thermocellum-like) species in an environmental sample (landfill leachate), possesses an autoinducing peptide (AIP) quorum-sensing (QS) gene, although it may not be functional. Methods and Results: A modified AIP accessory gene regulator (agr)C PCR protocol was performed on extracted DNA from a landfill leachate sample (also characterized by 16S rRNA gene cloning) and the PCR products were cloned, sequenced and phylogenetically analysed. It appeared that two agrC gene phylotypes existed, most closely related to the C. thermocellum agrC gene, differing by only 1 bp. Conclusions: It is possible to specifically identify and characterize the agrC AIP QS gene from uncultured Firmicutes (C. thermocellum-like) bacteria derived from environmental (landfill leachate) sample. Significance and Impact of the Study: This is the first successful attempt at identifying AIP QS genes from a cellulolytic environment (landfill). The agrC gene was identified as being most closely related to the C. thermocellum agrC gene, the same bacterium identified as being dominant, according to 16S rRNA gene cloning and subsequently fluorescence in situ hybridization analyses, in the same biomass.

Isolates of 'Candidatus Nostocoida limicola' Blackall et al. 2000 should be described as three novel species of the genus Tetrasphaera, as Tetrasphaera jenkinsii sp nov., Tetrasphaera vanveenii sp nov and Tetrasphaera veronensis sp nov.

Despite differences in their morphologies, comparative analyses of 16S rRNA gene sequences revealed high levels of similarity (> 94 %) between strains of the filamentous bacterium 'Candidatus Nostocoida limicola' and the cocci Tetrasphaera australiensis and Tetrasphaera japonica and the rod Tetrasphaera elongata, all isolated from activated sludge. These sequence data and their chemotaxonomic characters, including cell wall, menaquinone and lipid compositions and fingerprints of their 16S-23S rRNA intergenic regions, support the proposition that these isolates should be combined into a single genus containing six species, in the family Intrasporangiaceae in the Actinobacteria. This suggestion receives additional support from DNA-DNA hybridization data and when partial sequences of the rpoC1 gene are compared between these strains. Even though few phenotypic characterization data were obtained for these slowly growing isolates, it is proposed, on the basis of the extensive chemotaxonomic and molecular evidence presented here, that 'Candidatus N. limicola' strains Ben 17, Ben 18, Ben 67, Ben 68 and Ben 74 all be placed into the species Tetrasphaera jenkinsii sp. nov. (type strain Ben 74(T) = DSM 17519(T) = NCIMB 14128(T)), 'Candidatus N. limicola' strain Ben 70 into Tetrasphaera vanveenii sp. nov. (type strain Ben 70(T) = DSM 17518(T) = NCIMB 14127(T)) and 'Candidatus N. limicola' strains Ver 1 and Ver 2 into Tetrasphaera veronensis sp. nov. (type strain Ver 1(T) = DSM 17520(T) = NCIMB 14129(T)).

Kinetic and phylogenetic characterization of an anaerobic dechlorinating microbial community

The reductive dechlorination (RD) of tetrachloroethene (PCE) to vinyl chloride (VC) and, to a lesser extent, to ethene (ETH) by an anaerobic microbial community has been investigated by studying the processes and kinetics of the main physiological components of the consortium. Molecular hydrogen, produced by methanol-utilizing acetogens, was the electron donor for the PCE RD to VC and ETH without forming any appreciable amount of other chlorinated intermediates and in the near absence of methanogenic activity. The microbial community structure of the consortium was investigated by preparing a 1 6S rDNA clone library and by fluorescence in situ hybridization (FISH). The PCR primers used in the clone library allowed the harvest of 16SrDNA from both bacterial and archaeal members in the community. A total of 616 clones were screened by RFLP analysis of the clone inserts followed by the sequencing of RFLP group representatives and phylogenetic analysis. The clone library contained sequences mostly from hitherto undescribed bacteria. No sequences similar to those of the known RD bacteria like 'Dehalococcoides ethenogenes' or Dehalobacter restrictus were found in the clone library, and none of these bacteria was present in the RD consortium according to FISH. Almost all clones fell into six previously described phyla of the bacterial domain, with the majority (56(.)6%) being deep-branching members of the Spirochaetes phylum. Other clones were in the Firmicutes phylum (18(.)5%), the Chloroflexi phylum (16(.)4%), the Bacteroidetes phylum (6(.)3%), the Synergistes genus (11(.)1%) and a lineage that could not be affiliated with existing phyla (11(.)1%). No archaeal clones were found in the clone library. Owing to the phylogenetic novelty of the microbial community with regard to previously cultured microorganisms, no specific microbial component(s) could be hypothetically affiliated with the RD phenotype. The predominance of Spirochaetes in the microbial consortium, the main group revealed by clone library analysis, was confirmed by FISH using a purposely developed probe.

Metamorphosis of a scleractinian coral in response to microbial biofilms

Microorganisms have been reported to induce settlement and metamorphosis in a wide range of marine invertebrate species. However, the primary cue reported for metamorphosis of coral larvae is calcareous coralline algae (CCA). Herein we report the community structure of developing coral reef biofilms and the potential role they play in triggering the metamorphosis of a scleractinian coral. Two-week-old biofilms induced metamorphosis in less than 10% of larvae, whereas metamorphosis increased significantly on older biofilms, with a maximum of 41% occurring on 8-week-old microbial films. There was a significant influence of depth in 4- and 8-week biofilms, with greater levels of metamorphosis occurring in response to shallow-water communities. Importantly, larvae were found to settle and metamorphose in response to microbial biofilms lacking CCA from both shallow and deep treatments, indicating that microorganisms not associated with CCA may play a significant role in coral metamorphosis. A polyphasic approach consisting of scanning electron microscopy, fluorescence in situ hybridization (FISH), and denaturing gradient gel electrophoresis (DGGE) revealed that coral reef biofilms were comprised of complex bacterial and microalgal communities which were distinct at each depth and time. Principal-component analysis of FISH data showed that the Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, and Cytophaga-Flavobacterium of Bacteroidetes had the largest influence on overall community composition. A low abundance of Archaea was detected in almost all biofilms, providing the first report of Archaea associated with coral reef biofilms. No differences in the relative densities of each subdivision of Proteobacteria were observed between slides that induced larval metamorphosis and those that did not. Comparative cluster analysis of bacterial DGGE patterns also revealed that there were clear age and depth distinctions in biofilm community structure; however, no difference was detected in banding profiles between biofilms which induced larval metamorphosis and those where no metamorphosis occurred. This investigation demonstrates that complex microbial communities can induce coral metamorphosis in the absence of CCA.

Structure of circulin B and implications for antimicrobial activity of the cyclotides

The solution structure of one of the first members of the cyclotide family of macrocyclic peptides to be discovered, circulin B has been determined and compared with that of circulin A and related cyclotides. Cyclotides are mini-proteins derived from plants that have the characteristic features of a head-to-tail cyclised peptide backbone and a knotted arrangement of their three disulfide bonds. First discovered because of their uterotonic or anti-HIV activity, they have also been reported to have activity against a range of Gram positive and Gram negative bacteria as well as fungi. The aim of the current study was to develop structure-activity relationships to rationalise this antimicrobial activity. Comparison of cyclotide structures and activities suggests that the presence and location of cationic residues may be a requirement for activity against Gram negative bacteria. Understanding the topological differences associated with the antimicrobial activity of the cyclotides is of significant interest and potentially may be harnessed for pharmaceutical applications.

Marine actinomycetes related to the 'Salinospora' group from the Great Barrier Reef sponge Pseudoceratina clavata

Ten strains identified as marine actinomycetes related to the 'Salinospora ' group previously reported only from marine sediments were isolated from the Great Barrier Reef marine sponge Pseudoceratina clavata. The relationship of the isolates to 'Salinospora' was confirmed by phylogenetic analysis of 16S rRNA gene sequences. Colony morphology and pigmentation, occurrence and position of spores, and salinity requirements for growth were all consistent with this relationship. Genes homologous to beta-ketosynthase, an enzyme forming part of a polyketide synthesis complex, were retrieved from these isolates; these genes shared homology with other Type I ketosynthase genes, and phylogenetic comparison with amino acid sequences derived from database beta-ketosynthase genes was consistent with the close relationship of these isolates to the actinomycetes. Primers based on 16S rRNA gene sequences and designed for targeting amplification of members of the 'Salinospora' group via polymerase chain reaction have been used to demonstrate occurrence of these actinomycetes within the sponge tissue. In vitro bioassays of extracts from the isolates for antibiotic activity demonstrated that these actinomycetes have the potential to inhibit other sponge symbionts in vivo, including both Gram-negative and Gram-positive bacteria.

Culturable bacterial symbionts isolated from two distinct sponge species (Pseudoceratina clavata and Rhabdastrella globostellata) from the Great Barrier Reef display similar phylogenetic diversity

The diversity of the culturable microbial communities was examined in two sponge species-Pseudoceratina clavata and Rhabdastrella globostellata. Isolates were characterized by 16S rRNA gene sequencing and phylogenetic analysis. The bacterial community structures represented in both sponges were found to be similar at the phylum level by the same four phyla in this study and also at a finer scale at the species level in both Firmicutes and Alphaproteobacteria. The majority of the Alphaproteobacteria isolates were most closely related to isolates from other sponge species including alpha proteobacterium NW001 sp. and alpha proteobacterium MBIC3368. Members of the low %G + C gram-positive (phylum Firmicutes), high %G + C gram-positive (phylum Actinobacteria), and Cytophaga-Flavobacterium-Bacteroides (phylum Bacteroidetes) phyla of domain Bacteria were also represented in both sponges. In terms of culturable organisms, taxonomic diversity of the microbial community in the two sponge species displays similar structure at phylum level. Within phyla, isolates often belonged to the same genus-level monophyletic group. Community structure and taxonomic composition in the two sponge species P. clavata and Rha. globostellata share significant features with those of other sponge species including those from widely separated geographical and climatic regions of the sea.

PerR controls Mn-dependent resistance to oxidative stress in Neisseria gonorrhoeae

In previous studies it has been established that resistance to superoxide by Neisseria gonorrhoeae is dependent on the accumulation of Mn(II) ions involving the ABC transporter, MntABC. A mutant strain lacking the periplasmic binding protein component (MntC) of this transport system is hypersensitive to killing by superoxide anion. In this study the mntC mutant was found to be more sensitive to H2O2 killing than the wild-type. Analysis of regulation of MntC expression revealed that it was de-repressed under low Mn(II) conditions. The N. gonorrhoeae mntABC locus lacks the mntR repressor typically found associated with this locus in other organisms. A search for a candidate regulator of mntABC expression revealed a homologue of PerR, a Mn-dependent peroxide-responsive regulator found in Gram-positive organisms. A perR mutant expressed more MntC protein than wild-type, and expression was independent of Mn(II), consistent with a role for PerR as a repressor of mntABC expression. The PerR regulon of N. gonorrhoeae was defined by microarray analysis and includes ribosomal proteins, TonB-dependent receptors and an alcohol dehydrogenase. Both the mntC and perR mutants had reduced intracellular survival in a human cervical epithelial cell model.