Selected Topics in Anaerobic Bacteriology

Elevated rates and biased spectra of mutations in anaerobically cultured lactic acid bacteria

The rate, spectrum, and biases of mutations represent a fundamental force shaping biological evolution. Convention often attributes oxidative DNA damage as a major driver of spontaneous mutations. Yet, despite the contribution of oxygen to mutagenesis and the ecological, industrial, and biomedical importance of anaerobic organisms, relatively little is known about the mutation rates and spectra of anaerobic species. Here, we present the rates and spectra of spontaneous mutations assessed anaerobically over 1000 generations for three fermentative lactic acid bacteria species with varying levels of aerotolerance: Lactobacillus acidophilus, Lactobacillus crispatus, and Lactococcus lactis. Our findings reveal highly elevated mutation rates compared to the average rates observed in aerobically respiring bacteria with mutations strongly biased towards transitions, emphasizing the prevalence of spontaneous deamination in these anaerobic species and highlighting the inherent fragility of purines even under conditions that minimize oxidative stress. Beyond these overarching patterns, we identify several novel mutation dynamics: positional mutation bias around the origin of replication in Lb. acidophilus, a significant disparity between observed and equilibrium GC content in Lc. lactis, and repeated independent deletions of spacer sequences from within the CRISPR locus in Lb. crispatus providing mechanistic insights into the evolution of bacterial adaptive immunity. Overall, our study provides new insights into the mutational landscape of anaerobes, revealing how non-oxygenic factors shape mutation rates and influence genome evolution.

Integrating microbiome and metabolome revealed microbe-metabolism interactions in the stomach of patients with different severity of peptic ulcer disease

Background

Peptic ulcer disease (PUD) is a multi-cause illness with an unknown role for gastric flora and metabolism in its pathogenesis. In order to further understand the pathogenesis of gastric flora and metabolism in PUD, this study used histological techniques to analyze the microbiome and metabolome of gastric biopsy tissue. In this paper, our work described the complex interactions of phenotype-microbial-metabolite-metabolic pathways in PUD patients at different pathological stages.

Methods

Gastric biopsy tissue samples from 32 patients with chronic non-atrophic gastritis, 24 patients with mucosal erosions, and 8 patients with ulcers were collected for the microbiome. UPLC-MS metabolomics was also used to detect gastric tissue samples. These datasets were analyzed individually and integrated using various bioinformatics methods.

Results

Our work found reduced diversity of gastric flora in patients with PUD. PUD patients at different pathological stages presented their own unique flora, and there were significant differences in flora phenotypes. Coprococcus_2, Phenylobacterium, Candidatus_Hepatoplasma, and other bacteria were found in the flora of people with chronic non-atrophic gastritis (HC). The representative flora of mucosal erosion (ME) had uncultured_bacterium_c_Subgroup_6, Sphingomonadaceae, Xanthobacteraceae, and uncultured_bacterium_f_Xanthobacteraceae. In comparison, the characteristic flora of the PUD group was the most numerous and complex, including Ruminococcus_2, Agathobacter, Alistipes, Helicobacter, Bacteroides and Faecalibacterium. Metabolomics identified and annotated 66 differential metabolites and 12 significantly different metabolic pathways. The comprehensive analysis correlated microorganisms with metabolites at different pathological stages and initially explored the complex interactions of phenotype-microbial-metabolite-metabolic pathways in PUD patients at different pathological stages.

Conclusion

Our research results provided substantial evidence to support some data on the analysis of the microbial community and its metabolism in the stomach, and they demonstrated many specific interactions between the gastric microbiome and the metabolome. Our study can help reveal the pathogenesis of PUD and indicate plausible disease-specific mechanisms for future studies from a new perspective.

Antimicrobial susceptibility of anaerobic clinical isolates: A two-year surveillance

A total of 866 anaerobic strains isolated from clinical samples were tested by E-TEST for antimicrobial susceptibility. The most frequent antimicrobial resistance among the isolated genera, both Gram-positive and Gram-negative, was observed for clindamycin, and therefore, it cannot be considered as an empirical treatment. The antimicrobial resistance to benzylpenicillin was predominant among the Gram-negative bacteria, in particular the Bacteroides spp. The resistance percentages to meropenem and metronidazole are still low. However, metronidazole showed a considerable resistance in Finegoldia magna isolates, alone or in combination with other antibiotics. These data provide novel and useful epidemiological information on infections promoted by anaerobic bacteria.

Porphyromonas spp. have an extensive host range in ill and healthy individuals and an unexpected environmental distribution: A systematic review and meta-analysis

Studies on the anaerobic bacteria Porphyromonas, mainly focused on P. gingivalis, have revealed new bacterial structures, metabolic pathways, and physiologic functionalities. Porphyromonas are mainly described as being associated with mammals and involved in chronic oral infections and secondary pathologies such as cancers or neurodegenerative diseases. In this review, we collected and analyzed information regarding Porphyromonas isolation sites and associated conditions and showed that Porphyromonas are detected in numerous pristine and anthropic environments and that their host range appears wider than previously believed, including aquatic animals, arthropods, and birds, even if their predominant hosts remain humans, pets, and farm animals. Our analyses also revealed their presence in multiple organs and in a substantial proportion of healthy contexts. Overall, the growing numbers of microbiota studies have allowed unprecedented advances in the understanding of Porphyromonas ecology but raise questions regarding their phylogenic assignment. In conclusion, this systematic and meta-analysis provides an overview of current knowledge regarding Porphyromonas ecological distribution and encourages additional research to fill the knowledge gaps to better understand their environmental distribution and inter- and intra-species transmission.