Khelaifia, S. | Search bioRxiv

bioRxiv2019

Paradoxical β-lactamase activity of archaeal encoding enzymes

{beta}-lactams targeting the bacterial cell wall are not active on archaea. Here, we figure out that annotation of genes as {beta}-lactamase in Archeae on the basis of homologous genes, initially annotated {beta}-lactamases, is a remnant of the identification of the original activities of this group of enzymes, which in fact, have multiple functions including nuclease, ribonuclease, {beta}-lactamase, or glyoxalase; which may specialized over time. We expressed a class B {beta}-lactamase enzyme from Methanosarcina barkeri that digest penicillin G. Moreover, while a weak glyoxalase activity was detected, a significant ribonuclease activity on bacterial and synthetic RNAs was demonstrated. The {beta}-lactamase activity was inhibited by a {beta}-lactamase inhibitor (sulbactam), but its RNAse activity was not. This gene appears to has been transferred to the Flavobacteriaceae group including Elizabethkingia genus in which the expressed gene shows a more specialized activity toward resistance to tienanmicin but no glyoxalase activity. The expressed class C-like {beta}-lactamase gene, also from Methanosarcina sp., shows also hydrolysis activity and was more closely related to DD-peptidase enzymes than known bacterial class C {beta}-lactamases. Our findings highlight the requalification needness of annotated enzymes as {beta}-lactamases and the specification overtime of multipotent enzymes in different ways in Archaea and bacteria.

microbiology↗

bioRxiv2019

Antioxidants maintain Butyrate production by Human Gut Clostridia in the presence of Oxygen

BackgroundOxygen diffused from the human gut mucosa and shape the microbiota with a radial gradient of microbes according to their oxygen tolerance, while microbial and chemical oxygen consumption maintains the lumen in a deeply anaerobic state. Uncontrolled oxidative stress and hyperoxygenation have been reported as a pathogenic mechanism in Salmonella or Citrobacter rodentium infection, in patients with HIV and in severe acute malnutrition. We recently found that antioxidants allow strict anaerobes, including methanogenic archaea, to thrive in an oxidative environment (aerobic). Here, we tested the metabolomics switching of the 3 most odorous anaerobic microbes isolated from human gut when grown in aerobiosis with antioxidants.\n\nMethodsThree human gut Clostridia, Clostridium sporogenes, Clostridium lituseburense and Clostridium subterminale, isolated by culturomics, were grown in anaerobiosis or in aerobiosis with antioxidants. Gaz and liquid chromatography-Mass spectrometry (GC/MS and LC/MS) were used for metabolomics analysis.\n\nResultsAn unexpected global dichotomic metabolomic switching from thiols, alcohols and short-chain fatty acid esters to a specific aerobic metabolic repertoire with the production of alkanes, cycloheptatriene and, paradoxically, increased butyrate production, was observed. Analysis of polar metabolites confirmed the discovery of an unexplored aerobic metabolic repertoire, including the production of specific dipeptides and several lysophospholipids, thus unraveling unsuspected human gut microbiome capacities.\n\nConclusionsAntioxidants unraveled an unexplored aerobic metabolic repertoire of human gut Clostridia. The increased production of butyrate suggests that antioxidants contribute to the maintenance and the active resilience of the human gut microbiome against oxidative aggression, as during Salmonella infection.

microbiology↗