Biology subjects

Pudlo, N. A.

Publications and source records attributed to Pudlo, N. A..

8 recordsLinked to original sources

bioRxiv2026

Degradation of mucin O-glycans by a human gut symbiont requires a complex enzyme repertoire and promotes colonization

Secreted mucins are the major component of the mucus layer that protects intestinal epithelial surfaces by blocking excessive interactions with the microbiota. Mucins are complex glycoproteins decorated with over 100 different O-glycans. Some bacteria can utilize mucins and excessive degradation has been associated with disruption of the mucus barrier and inflammation. Despite the importance of mucins, a detailed enzymatic pathway by which gut bacteria degrade colonic mucin O-glycans and the impact of this process on gut colonization are unknown. Here, we identified >100 genes that are expressed by the symbiont Bacteroides thetaiotaomicron during growth on different O-glycan substrates, revealing effects of glycan structure on gene expression. The characterization of 33 glycoside hydrolase enzymes revealed the pathway for colonic O-glycan degradation by this bacterium. In vivo competition experiments show that multiple exo-acting enzymes targeting mucin capping structures are central to gut colonization and may provide targets to inhibit bacterial mucin degradation.

microbiology↗

bioRxiv2026

Identification and characterization of the functional LolB ortholog in Bacteroides

Bacteroidota are prolific members of the human gut microbiota, influencing overall health through the degradation of various polysaccharides. To aid in this process, these bacteria deploy cell surface lipoproteins, proteins anchored to the membrane by a lipidated N-terminal cysteine. Despite their importance, lipoprotein synthesis and transport in Bacteroidota is not well defined, particularly how lipoproteins reach the outer membrane and cell surface. In Escherichia coli, lipoproteins are inserted into the outer membrane by LolB, the final step of the Lol pathway for localizing lipoproteins, previously thought to be confined to {gamma}- and {beta}-proteobacteria. Herein, we report a structural ortholog of LolB in Bacteroides that rescues the lethal phenotype associated with LolB depletion in E. coli. We demonstrate this orthologs LolB-like activity through mutagenesis studies and a lipoprotein insertion activity assay. We find that the gene cannot be deleted from Bacteroides, but that depletion does not significantly impact growth on polysaccharides, nor the surface localization of lipoproteins involved in starch degradation. Nonetheless, depletion significantly alters the composition of many proteins in both the inner and outer membranes, while others remain unchanged. Altogether, our findings contribute to elucidating the lipoprotein transport pathway in Bacteroides and how it impacts cell physiology. ImportanceBacteroidota are abundant members of the human gut microbiota that influence health and disease. These bacteria deploy numerous cell surface lipoproteins that mediate their interactions with the host and play key roles in cell physiology. However, their mechanism(s) of lipoprotein transport is understudied. Here, we used a genetic screen to identify orthologs to E. coli LolB, the protein responsible for lipoprotein insertion into the outer membrane. Our screen revealed a structural ortholog to LolB in Bacteroides that performs this function. We show that when LolB is depleted, lipoproteins still reach the cell surface, even though the overall protein composition of the membrane is significantly altered. Our results broaden the understanding of both lipoprotein transport and Bacteroidota physiology.

microbiology↗

bioRxiv2025

Carbohydrates and the oxidative branch of the pentose phosphate pathway modify Bacteroides thetaiotaomicron phage resistance by phase variable S-layers

The human gut microbiota consists of hundreds of bacterial species, some of which persist in the presence of lytic phage that infect them. Bacteroides employ numerous phase-variable strategies to survive in the presence of phage, including capsular polysaccharides (CPS) and S-layer lipoproteins. We previously reported that a Bacteroides thetaiotaomicron strain lacking CPS exhibits almost complete resistance to multiple phages when forced to express the S-layer protein BT1927. However, this strain was only resistant after certain growth conditions, suggesting nutritional variables alter infection and resistance. We grew this strain on various simple sugars and polysaccharides finding that some substrates (fructose, glucose) promote strong resistance to a single phage (ARB25) while others like N-acetylgalactosamine (GalNAC) and mucin O-glycans increase susceptibility. Mixing fructose and GalNAc indicates the effects of GalNAc are dominant. Despite increasing ARB25 susceptibility, GalNAc did not reduce BT1927 transcript or protein levels. Instead, GalNAc reduced the amount of BT1927 displayed on the cell surface and increased outer membrane vesiculation. Mutants in any of the 3 steps of the oxidative branch of the pentose phosphate pathway--grown in fructose--behaved similarly to wild-type cells grown in GalNAc, illuminating this pathway in regulation of sugar-mediated phage-resistance. Despite promoting strong resistance, cells grown in glucose/fructose sometimes displayed sub-populations that appeared to completely lack surface BT1927, suggesting another checkpoint exists to control whether this phage defense is deployed. Finally, we show the mucin sugar GalNAc increases susceptibility to several other phage, which has implications for B. thetaiotaiomicron persistence in niches like the mucus layer. ImportanceThe persistence of viruses that infect bacteria (bacteriophages or phages) in the human gut microbiome and their effects on bacterial physiology and host health are active areas of investigation. Our study investigates how various sugars and polysaccharides alter phage susceptibility and resistance in the model gut symbiont Bacteroides thetaiotaomicron to lytic phages that are capable of infecting it. Our finding that the mucin sugar, N-acetylgalactosamine, and mucin O-glycans that contain this sugar reduce B. thetaiotaomicron resistance to multiple phages has implications for how this symbiont persists in different gut microhabitats, such as the mucus layer, and which defense mechanisms it can deploy to survive in these niches.

microbiology↗

bioRxiv2024

Acarbose Impairs Gut Bacteroides Growth by Targeting Intracellular GH97 Enzymes

Acarbose is a type-2 diabetes medicine that inhibits dietary starch breakdown into glucose by inhibiting host amylase and glucosidase enzymes. Numerous gut species in the Bacteroides genus enzymatically break down starch and change in relative abundance within the gut microbiome in acarbose-treated individuals. To mechanistically explain this observation, we used two model starch-degrading Bacteroides, Bacteroides ovatus (Bo) and Bacteroides thetaiotaomicron (Bt). Bt growth is severely impaired by acarbose whereas Bo growth is not. The Bacteroides use a starch utilization system (Sus) to grow on starch. We hypothesized that Bo and Bt Sus enzymes are differentially inhibited by acarbose. Instead, we discovered that although acarbose primarily targets the Sus periplasmic GH97 enzymes in both organisms, the drug affects starch processing at multiple other points. Acarbose competes for transport through the Sus beta-barrel proteins and binds to the Sus transcriptional regulators. Further, Bo expresses a non-Sus GH97 (BoGH97D) when grown in starch with acarbose. The Bt homolog, BtGH97H, is not expressed in the same conditions, nor can overexpression of BoGH97D complement the Bt growth inhibition in the presence of acarbose. This work informs us about unexpected complexities of Sus function and regulation in Bacteroides, including variation between related species. Further, this indicates that the gut microbiome may be a source of variable response to acarbose treatment for diabetes. ImportanceAcarbose is a type 2 diabetes medication that works primarily by stopping starch breakdown into glucose in the small intestine. This is accomplished by inhibition of host enzymes, leading to better blood sugar control via reduced ability to derive glucose from dietary starches. The drug and undigested starch travel to the large intestine where acarbose interferes with the ability of some bacteria to grow on starch. However, little is known about how gut bacteria interact with acarbose, including microbes that can use starch as a carbon source. Here, we show that two gut species, Bacteroides ovatus (Bo) and Bacteroides thetaiotaomicron (Bt), respond differently to acarbose: Bt growth is inhibited by acarbose while Bo growth is not. We reveal a complex set of mechanisms involving differences in starch import and sensing behind the different Bo and Bt responses. This indicates the gut microbiome may be a source of variable response to acarbose treatment for diabetes via complex mechanisms in common gut microbes.

microbiology↗

bioRxiv2021

Phenotypic and genomic diversification in complex carbohydrate degrading human gut bacteria

Symbiotic bacteria are responsible for the majority of complex carbohydrate digestion in the human colon. Since the identities and amounts of dietary polysaccharides directly impact the gut microbiota, determining which microorganisms consume specific nutrients is central to defining the relationship between diet and gut microbial ecology. Using a custom phenotyping array, we determined carbohydrate utilization profiles for 354 members of the Bacteroidetes, a dominant saccharolytic phylum. There was wide variation in the numbers and types of substrates degraded by individual bacteria, but phenotype-based clustering grouped members of the same species indicating that each species performs characteristic roles. The ability to utilize dietary polysaccharides and endogenous mucin glycans was negatively correlated, suggesting exclusion between these niches. By analyzing related Bacteroides ovatus/xylanisolvens strains that vary in their ability to utilize mucin glycans, we addressed whether gene clusters that confer this complex, multi-locus trait are being gained or lost in individual strains. Pangenome reconstruction of these strains revealed a remarkably mosaic architecture in which genes involved in polysaccharide metabolism are highly variable and bioinformatics data provide evidence of interspecies gene transfer that might explain this genomic heterogeneity. Global transcriptomic analyses suggest that the ability to utilize mucin has been lost in some lineages of B. ovatus and B. xylanisolvens, which still harbor residual gene clusters that are involved in mucin utilization by strains that still actively express this phenotype. Our data provide insight into the breadth and complexity of carbohydrate metabolism in the microbiome and the underlying genomic events that shape these behaviors.

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↗

bioRxiv2020

A single bacterial sulfatase is required for metabolism of colonic mucin O-glycans and intestinal colonization by a symbiotic human gut bacterium

Humans have co-evolved with a dense community of microbial symbionts that inhabit the lower intestine. In the colon, secreted mucus creates a physical barrier that separates these microbes from the intestinal epithelium. Some gut bacteria are able to utilize mucin glycoproteins, the main mucus component, as a nutrient source. However, it remains unclear which bacterial enzymes initiate the degradation of the highly complex O-glycans found in mucins. In the colon, these glycans are heavily sulfated, but the specific sulfatases that are active on colonic mucins have not been identified. Here, we show that sulfatases are essential to the utilization of colonic mucin O-glycans by the human gut symbiont Bacteroides thetaiotaomicron. We have characterized the activity of 12 different sulfatases encoded by this species, showing that these enzymes collectively are active on all of the known sulfate linkages in colonic O-glycans. Crystal structures of 3 enzymes provide mechanistic insight into the molecular basis of substrate-specificity. Unexpectedly, we found that a single sulfatase is essential for utilization of sulfated O-glycans in vitro and also plays a major role in vivo. Our results provide insight into the mechanisms of mucin degradation by gut bacteria, an important process for both normal microbial gut colonization and diseases such as inflammatory bowel disease (IBD). Sulfatase activity is likely to be a keystone step in bacterial mucin degradation and inhibition of these enzymes may therefore represent a viable therapeutic path for treatment of IBD and other diseases.

microbiology↗

bioRxiv2020

Extensive transfer of genes for edible seaweed digestion from marine to human gut bacteria

Humans harbor numerous species of colonic bacteria that digest the fiber polysaccharides in commonly consumed terrestrial plants. More recently in history, regional populations have consumed edible macroalgae seaweeds containing unique polysaccharides. It remains unclear how extensively gut bacteria have adapted to digest these nutrients and use these abilities to colonize microbiomes around the world, especially outside Asia. Here, we show that the ability of gut bacteria to digest seaweed polysaccharides is more pervasive than previously appreciated. Using culture-based approaches, we show that known Bacteroides genes involved in seaweed degradation have mobilized into many members of this genus. We also identify several previously unknown examples of marine bacteria-derived genes, and their corresponding mobile DNA elements, that are involved in degrading seaweed polysaccharides. Some of these genes reside in gut-resident, Gram-positive Firmicutes, for which phylogenetic analysis suggests an origin in the Epulopiscium gut symbionts of marine fishes. Our results are important for understanding the metabolic plasticity of the human gut microbiome, the global exchange of genes in the context of dietary selective pressures and identifying new functions that can be introduced or engineered to design and fill orthogonal niches for a future generation of engineered probiotics.

microbiology↗