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Anaerobic clinical microbiology remains a challenge due to specialist culture requirements, coupled with the increase in and spread of antimicrobial resistance. The normal human microbiota is primarily composed of anaerobic bacteria, and is now recognised as a source of life-threatening anaerobic infection. More recent metataxonomic and metagenomic sequencing has extended interest in the potential role of the microbiota in a plethora of other aspects of human health, from obesity to mental health. In addition, the successful use of faecal microbiota transplants for the treatment of clostridial infection raises potential unchartered long-term consequences and possibilities.

In conjunction with Anaerobe 2019, this collection will provide scientific insights into the future impact of anaerobic bacteria in human health and disease, addressing the implications of recent microbiota studies as well as the continued threat of emerging and re-emerging anaerobic infection. 

This collection is now open for submissions – please submit your article here, stating that your manuscript is part of the Anaerobe collection.  


Collection Contents

4 results

    • RelA/DTD-mediated regulation of spore formation and toxin production by type A strain SM101

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      RelA is a global regulator for stationary phase development in the model bacterium . The gene forms a bicistronic operon with the downstream gene. In this study, we evaluated the significance of RelA and DTD proteins in spore formation and toxin production by an important gastrointestinal pathogen . Our β-glucuronidase assay showed that in strain SM101, forms a bicistronic operon with its downstream gene, and the promoter is expressed during both vegetative and sporulation conditions. By constructing double and single mutants in SM101, we found that: (1) RelA is required for maintaining the efficient growth capacity of SM101 cells during vegetative conditions; (2) both RelA and DTD are required for spore formation and enterotoxin (CPE) production by SM101; (3) RelA/DTD activate CodY, which is known to activate spore formation and CPE production in SM101 by activating a key sporulation-specific σ factor F; (4) as expected, RelA/DTD activate sporulation-specific σ factors (σ, σ, σ and σ) by positively regulating Spo0A production; and finally (5) RelA, but not DTD, negatively regulates phospholipase C (PLC) production by repressing gene expression. Collectively, our results demonstrate that RelA modulates cellular physiology such as growth, spore formation and toxin production by type A strain SM101, although DTD also plays a role in these pleiotropic functions in coordination with RelA during sporulation. These findings have implications for the understanding of the mechanisms involved in the infectious cycle of .

    • hydrogen sulfide enhances methyl mercaptan-induced pathogenicity in mouse abscess formation

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      produces hydrogen sulfide (HS) from -cysteine. However, the role of HS produced by in periodontal inflammation is unclear. In this study, we identified the enzyme that catalyses HS production from -cysteine and analysed the role of HS using a mouse abscess model. The enzyme identified was identical to methionine γ-lyase (PG0343), which produces methyl mercaptan (CHSH) from -methionine. Therefore, we analysed HS and CHSH production by W83 and a PG0343-deletion mutant (ΔPG0343) with/without -cysteine and/or -methionine. The results indicated that CHSH is produced constitutively irrespective of the presence of -methionine, while HS was greatly increased by both W83 and ΔPG0343 in the presence of -cysteine. In contrast, CHSH production by ΔPG0343 was absent irrespective of the presence of -methionine, and HS production was eliminated in the absence of -cysteine. Thus, CHSH and HS production involves different substrates, -methionine or -cysteine, respectively. Based on these characteristics, we analysed the roles of CHSH and HS in abscess formation in mice by W83 and ΔPG0343. Abscess formation by W83, but not ΔPG0343, differed significantly in the presence and absence of -cysteine. In addition, the presence of -methionine did not affect the size of abscesses generated by W83 and ΔPG0343. Therefore, we conclude that HS produced by does not induce inflammation; however, HS enhances inflammation caused by CHSH. Thus, these results suggest the HS produced by plays a supportive role in inflammation caused by methionine γ-lyase.

    • Recombinant expression and characterisation of the oxygen-sensitive 2-enoate reductase from

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      ‘Ene’-reductases have attracted significant attention for the preparation of chemical intermediates and biologically active products. To date, research has been focussed primarily on Old Yellow Enzyme-like proteins, due to their ease of handling, whereas 2-enoate reductases from clostridia have received much less attention, because of their oxygen sensitivity and a lack of suitable expression systems. A hypothetical 2-enoate reductase gene, , was identified in DSM 795. The encoded protein shares a high degree of homology to clostridial FMN- and FAD-dependent 2-enoate reductases, including the cinnamic acid reductase proposed to be involved in amino acid metabolism in proteolytic clostridia. The gene was cloned and overexpressed in Successful expression depended on the use of strictly anaerobic conditions for both growth and enzyme preparation, since FldZ was oxygen-sensitive. The enzyme reduced aromatic enoates, such as cinnamic acid or -coumaric acid, but not short chain unsaturated aliphatic acids. The β,β-disubstituted nitroalkene, -1-nitro-2-phenylpropene, was reduced to enantiopure -1-nitro-2-phenylpropane with a yield of 90 %. By contrast, the β-disubstituted nitroalkene, -2-nitro-1-phenylpropene, was reduced with a moderate yield of 56 % and poor enantioselectivity (16 % ee for -2-nitro-1-phenylpropane). The availability of an expression system for this recombinant clostridial 2-enoate reductase will facilitate future characterisation of this unusual class of ‘ene’-reductases, and expand the biocatalytic toolbox available for enantioselective hydrogenation of carbon-carbon double bonds.

    • Discovery of a novel lantibiotic nisin O from A2-162, isolated from the human gastrointestinal tract

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      A novel -like sequence was identified from the dominant human gut bacterium strain A2-162. This sequence was extended to reveal a putative lantibiotic operon with biosynthetic and transport genes, two sets of regulatory genes, immunity genes, three identical copies of a nisin-like gene with an unusual leader peptide, and a fourth putative gene. Comparison with other nisin clusters showed that the closest relationship was to nisin U. A2-162 demonstrated antimicrobial activity against when grown on solid medium in the presence of trypsin. Fusions of predicted structural sequences with the nisin A leader were expressed in containing the nisin A operon without . Expression of the leader sequence fused to the predicted structural produced a growth defect in that was dependent upon the presence of biosynthetic genes, but failed to produce antimicrobial activity. Insertion of the cluster into MG1614 gave an increased immunity to nisin A, but this was not replicated by the expression of . Nisin A induction of containing the cluster and genes allowed detection of the NsoA1 pre-peptide by Western hybridization. When this heterologous producer was grown with nisin induction on solid medium, antimicrobial activity was demonstrated in the presence of trypsin against , and . This research adds to evidence that lantibiotic production may be an important trait of gut bacteria and could lead to the development of novel treatments for intestinal diseases.

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