Biology subjects

Schnizlein, M. K.

Publications and source records attributed to Schnizlein, M. K..

4 recordsLinked to original sources

bioRxiv2025

Non-redundant cardiolipin synthases support membrane integrity and stress resilience in Bacteroides fragilis

Gut-resident bacteria must tolerate diverse membrane-disrupting agents, including bile acids, to maintain colonization. Cardiolipin is an anionic phospholipid that supports membrane integrity and stress resilience in many bacteria. However, cardiolipin synthases remain poorly characterized in the Bacteroidota, a dominant phylum of the human gut microbiota. The prevalent gut commensal Bacteroides fragilis encodes two predicted cardiolipin synthases, ClsA and ClsB. We previously identified both cls genes as bile-acid fitness factors in B. fragilis P207, but the individual contributions of ClsA and ClsB to cell physiology had remained undefined. Here we combine targeted gene deletion with high-resolution lipidomics, metabolomics, and elemental mass spectrometry to show that the two enzymes have non-redundant functions in the cell. Cardiolipin is a minor lipid in the B. fragilis membrane, and both Cls enzymes contribute to its production. clsA and clsB differ in growth-phase expression, in their effects on cell morphology, and in their associated cardiolipin species. Loss of each enzyme also produces distinct changes in fitness under several membrane-perturbing stresses and in the broader cellular metabolome, including compound classes with documented bioactivity in mammalian hosts. In contrast to the acute ion-gradient disruption caused by the secondary bile acid deoxycholate, deletion of both synthases did not measurably alter steady-state intracellular ion levels under standard growth conditions, indicating that cardiolipin loss does not perturb basal ion homeostasis under these conditions. Together, these results define non-redundant roles for two cardiolipin synthases in a common member of the human gut microbiota. ImportanceInflammatory bowel diseases affect millions of people worldwide. The gut bacterium Bacteroides fragilis is a normal member of the human intestinal microbiota that can also bloom to high abundance in inflamed guts. To survive within the gut, B. fragilis must maintain the integrity and function of its cell membrane. In this study, we characterize the functional role of two B. fragilis genes that contribute to the synthesis of the membrane lipid, cardiolipin. We find that the two cardiolipin synthase genes are not functionally interchangeable; each impacts the cells lipid pool in distinct ways and contributes differently to how B. fragilis responds to membrane stress. Our work provides insight into how a common gut bacterium adapts to conditions encountered in the intestine, and improves understanding of membrane biology in this important group of gut microbes.

microbiology↗

bioRxiv2022

Differences in Gut Microbiota Assembly Alter Its Ability to Metabolize Dietary Polysaccharides and Resist Clostridioides difficile Colonization

The mammalian gut is home to a vibrant community of microbes. As the gut microbiota has evolved, its members have formed a complex yet stable relationships that prevent non-indigenous microorganisms, such as Clostridioides difficile, from establishing within the gut. Using a bioreactor model of the gut, we characterize how variation in microbial community assembly changes its ability to resist C. difficile. We established diluted microbial communities from healthy human stool in a bioreactor gut model and subsequently challenged them with vegetative C. difficile. 16S rRNA-gene sequencing and selective plating revealed that dilution progressively increases microbiota variability and decreases C. difficile colonization resistance. Using Dirichlet Multinomial Mixtures and linear discriminant analysis of effect size, we identified 19 bacterial taxa, including Bifidobacterium, Bacteroides and Lachnospiraceae, that associate with more resistant community types. Since these taxa are associated with butyrate production, which is tied to C. difficile colonization resistance, we performed another reactor experiment where we increased inulin concentrations prior to C. difficile challenge. Diluted communities concurrently lost their ability to produce additional butyrate in response to inulin, as measured by high performance liquid chromatography, and resist C. difficile colonization. These data demonstrate that a similar level of microbiota cohesiveness is required to prevent C. difficile colonization and metabolize inulin. It also suggests that metabolic activity of butyrate-producing microbes is tied to colonization resistance. Future work can leverage these findings to develop treatments that leverage knowledge of these ecological dynamics to improve efficacy. ImportanceThe microbes living in the human large intestine helps create an environment that is resistant to organisms that do not normally reside there, such as the pathogen Clostridioides difficile. Differences in ways in which microbial communities make an environment their home can change their ability to provide that resistance. To study those differences, we use a model of the intestine that incorporates only microbial variables (i.e. no host is involved). By diluting microbial communities to decrease their complexity, we show that communities lose their ability to resist C. difficile at a particular point and, at the same time, their ability to use inulin, a common dietary fiber, in ways that make the environment more toxic to C. difficile. These findings will help future researchers dissect the microbial components that create a resistant intestinal environment.

microbiology↗

bioRxiv2021

The Food Additive Xanthan Gum Drives Adaptation of the Human Gut Microbiota

The diets of industrialized countries reflect the increasing use of processed foods, often with the introduction of novel food additives. Xanthan gum is a complex polysaccharide with unique rheological properties that have established its use as a widespread stabilizer and thickening agent1. However, little is known about its direct interaction with the gut microbiota, which plays a central role in digestion of other, chemically-distinct dietary fiber polysaccharides. Here, we show that the ability to digest xanthan gum is surprisingly common in industrialized human gut microbiomes and appears to be contingent on the activity of a single bacterium that is a member of an uncultured bacterial genus in the family Ruminococcaceae. We used a combination of enrichment culture, multi-omics, and recombinant enzyme studies to identify and characterize a complete pathway in this uncultured bacterium for the degradation of xanthan gum. Our data reveal that this keystone degrader cleaves the xanthan gum backbone with a novel glycoside hydrolase family 5 (GH5) enzyme before processing the released oligosaccharides using additional enzymes. Surprisingly, some individuals harbor a Bacteroides species that is capable of consuming oligosaccharide products generated by the keystone Ruminococcaceae or a purified form of the GH5 enzyme. This Bacteroides symbiont is equipped with its own distinct enzymatic pathway to cross-feed on xanthan gum breakdown products, which still harbor the native linkage complexity in xanthan gum, but it cannot directly degrade the high molecular weight polymer. Thus, the introduction of a common food additive into the human diet in the past 50 years has promoted the establishment of a food chain involving at least two members of different phyla of gut bacteria.

microbiology↗

bioRxiv2019

Dietary xanthan gum alters antibiotic efficacy against the murine gut microbiota and attenuates Clostridioides difficile colonization

Dietary fiber provides a variety of microbiota-mediated benefits ranging from anti-inflammatory metabolites to pathogen colonization resistance. A healthy gut microbiota protects against Clostridioides difficile colonization. Manipulation of these microbes through diet may increase colonization resistance to improve clinical outcomes. The primary objective of this study was to identify how the dietary fiber xanthan gum affects the microbiota and C. difficile colonization.\n\nWe added 5% xanthan gum to the diet of C57Bl/6 mice and examined its effect on the microbiota through 16S rRNA-gene amplicon sequencing and short-chain fatty acid analysis. Following either cefoperazone or an antibiotic cocktail administration, we challenged mice with C. difficile and measured colonization by monitoring colony-forming units.\n\nXanthan gum administration associates with increases in fiber degrading taxa and short-chain fatty acid concentrations. However, by maintaining both the diversity and absolute abundance of the microbiota during antibiotic treatment, the protective effects of xanthan gum administration on the microbiota were more prominent than the enrichment of these fiber degrading taxa. As a result, mice that were on the xanthan gum diet experienced limited to no C. difficile colonization.\n\nXanthan gum administration alters mouse susceptibility to C. difficile colonization by maintaining the microbiota during antibiotic treatment. While antibiotic-xanthan gum interactions are not well understood, xanthan gum has previously been used to bind drugs and alter their pharmacokinetics. Thus, xanthan gum may alter the activity of the oral antibiotics used to make the microbiota susceptible. Future research should further characterize how this and other common dietary fibers interact with drugs.\n\nIMPORTANCEA healthy gut bacterial community benefits the host by breaking down dietary nutrients and protecting against pathogens. Clostridioides difficile capitalizes on the absence of this community to cause diarrhea and inflammation. Thus, a major clinical goal is to find ways to increase resistance to C. difficile colonization by either supplementing with bacteria that promote resistance or a diet to enrich for those already present in the gut. In this study, we describe an interaction between xanthan gum, a human dietary additive, and the microbiota resulting in an altered gut environment that is protective against C. difficile colonization.

microbiology↗