Biology subjects

Calcutt, M. W.

Publications and source records attributed to Calcutt, M. W..

4 recordsLinked to original sources

bioRxiv2026

Rational engineering of facultative anaerobiosis enables commensal survival in the oxygenated gut

Life originated in the absence of oxygen. Despite its substantial energetic advantages, many modern microbes remain obligate anaerobes, confined to anoxic niches such as the mammalian gut. Why these organisms cannot tolerate oxygen has remained unresolved for more than two centuries. Here, using integrated multi-omics analyses, we identify a network of interlocking vulnerabilities in central metabolism, biosynthetic pathways, and redox homeostasis that together impose an aerobic growth barrier in the obligate anaerobic commensal Bacteroides thetaiotaomicron. Rational repair of these vulnerabilities restores metabolic integrity and progressively enhances oxygen tolerance, yielding engineered strains capable of robust growth at 10% O2 and markedly improved resilience in the oxygenated, inflamed gut. These findings define a molecular basis for obligate anaerobiosis and establish a framework for engineering commensal bacteria to function in oxidative environments, expanding their ecological range and therapeutic potential.

microbiology↗

bioRxiv2025

An Anaerobic Pathogen Rewires Host Metabolism to Fuel Oxidative Growth in the Inflamed Gut

To colonize their host and cause disease, enteric pathogens must deploy their virulence factors to establish distinct nutrient niches. How obligate anaerobic pathogens construct nutrient niches in the densely populated large intestine remains poorly understood. Enterotoxigenic Bacteroides fragilis (ETBF) is considered an obligate anaerobic bacterium and has been implicated in inflammation-associated diseases, including colitis and colorectal cancer. Here we show that ETBF uses its virulence factor, Bacteroides fragilis toxin, to reprogram colonic epithelial cell metabolism to colonize the inflamed gut. Bacteroides fragilis toxin activates colonic epithelial signaling and hijacks the host bile acid recycling pathway, inducing a metabolic shift in the epithelium from oxidative phosphorylation to glycolysis. This shift increases local concentrations of lactate and oxygen, nutrients that support an oxidative metabolism in ETBF. These findings reveal an unexpected strategy by which a pathogenic organism, previously considered to be an obligate anaerobic bacterium, generates and exploits an oxidative niche in the inflamed gut.

microbiology↗

bioRxiv2024

B cell expression of the enzyme PexRAP, an intermediary in ether lipid biosynthesis, promotes antibody responses and germinal center size

The qualities of antibody (Ab) responses provided by B lymphocytes and their plasma cell (PC) descendants are crucial facets of responses to vaccines and microbes. Metabolic processes and products regulate aspects of B cell proliferation and differentiation into germinal center (GC) and PC states as well as Ab diversification. However, there is little information about lymphoid cell-intrinsic functions of enzymes that mediate ether lipid biosynthesis, including a major class of membrane phospholipids. Imaging mass spectrometry (IMS) results had indicated that concentrations of a number of these phospholipids were substantially enhanced in GC compared to the background average in spleens. However, it was not clear if biosynthesis in B cells was a basis for this finding, or whether such cell-intrinsic biosynthesis contributes to B cell physiology or Ab responses. Ether lipid biosynthesis can involve the enzyme PexRAP, the product of the Dhrs7b gene. Using combinations of IMS and immunization experiments in mouse models with inducible Dhrs7b loss-of-function, we now show that B lineage-intrinsic expression of PexRAP promotes the magnitude and affinity maturation of a serological response. Moreover, the data revealed a Dhrs7b-dependent increase in ether phospholipids in primary follicles with a more prominent increase in GC. Mechanistically, PexRAP impacted B cell proliferation via enhanced survival associated with controlling levels of ROS and membrane peroxidation. These findings reveal a vital role of this peroxisomal enzyme in B cell homeostasis and the physiology of humoral immunity.

immunology↗

bioRxiv2021

Salmonella Typhimurium uses anaerobic respiration to overcome propionate-mediated colonization resistance

The gut microbiota benefits the host by limiting enteric pathogen expansion (colonization resistance) partially via the production of inhibitory metabolites. Propionate, a short-chain fatty acid produced by microbiota members, is proposed to mediate colonization resistance against Salmonella enterica serovar Typhimurium (S. Tm). Here, we show that S. Tm overcomes the inhibitory effects of propionate by using it as a carbon source for anaerobic respiration. We determined that propionate metabolism provides an inflammation-dependent colonization advantage to S. Tm during infection. Such benefit was abolished in the intestinal lumen of Salmonella-infected germ-free mice. Interestingly, S. Tm propionate-mediated intestinal expansion was restored when germ-free mice were monocolonized with Bacteroides thetaiotaomicron (B. theta), a prominent propionate producer in the gut, but not when mice were monocolonized with a propionate production-deficient B. theta strain. Taken together, our results reveal a novel strategy used by S. Tm to mitigate colonization resistance by metabolizing microbiota-derived propionate.

microbiology↗