Biology subjects

Goulian, M.

Publications and source records attributed to Goulian, M..

7 recordsLinked to original sources

bioRxiv2026

Resident and Engrafting E. coli Populations Expand Through Dissimilar Pathways in the Inflamed Gut

Intestinal inflammation increases the abundance of Enterobacteriaceae in the gastrointestinal tract by several orders of magnitude. These population expansions, or blooms, are associated with disease progression and have been suggested to exacerbate intestinal pathologies in some settings. Murine studies have shown that during the early stages of Escherichia coli colonization, i.e., during engraftment, inflammation enhances fitness through processes that depend on Moco, an enzyme cofactor found in a variety of oxidoreductases that consists of molybdenum coordinated by a pterin molecule. Using a murine commensal E. coli isolate and a DSS-induced colitis model in mice, we investigated whether Moco is also important for blooms of E. coli that are part of the resident microbiota, that is, for E. coli that have engrafted well before the onset of inflammation. We show that resident wild-type and Moco- E. coli exhibit comparable expansions in response to inflammation, indicating that, in this context, Moco-dependent processes such as nitrate respiration or formate oxidation were not important for inflammation-induced blooms. We find that Moco is important, however, for E. coli colonization in the absence of inflammation, suggesting that alternative respiratory pathways or other Moco-dependent processes are necessary for E. coli colonization of a healthy murine gut. Our findings demonstrate that the mechanisms underlying inflammation-induced blooms can depend on the temporal relationship between engraftment and inflammation, and also highlight the importance of considering colonization stage in identifying and interpreting the factors that affect the fitness of microbes colonizing the intestine.

microbiology↗

bioRxiv2025

Platelet factor 4 modulates endothelial cell antimicrobial activity to enhance bacterial clearance and improve sepsis outcomes

Sepsis is a life-threatening condition characterized by dysregulated host responses to infection. Here, we identify platelet factor 4 (PF4) as a key mediator of vascular antimicrobial defense. In vitro, PF4 enhanced endothelial cell internalization of Escherichia coli via interactions with the PF4 receptor CXCR3 and the endothelial glycocalyx, directing bacteria to clathrin-mediated endocytosis and lysosomal degradation. In vivo, PF4 administration improved survival and reduced sepsis severity, bacterial burden, inflammation, and thrombosis in wild-type (WT) and PF4 knockout (PF4-/-) mice challenged with systemic polymicrobial infection. Using intravital microscopy, we observed that infused bacteria were rapidly sequestered in the pulmonary microvasculature. However, PF4-/- mice exhibited impaired bacterial clearance and increased microvascular platelet adhesion and aggregation. In the liver, following Kupffer cell depletion, PF4-/- mice had increased sinusoidal platelet accumulation, larger bacterial aggregates, and elevated hepatic bacterial burden compared to WT controls. Collectively, these findings reveal that PF4 promotes bacterial clearance and restrains immunothrombosis during sepsis in part via endothelial cell uptake and destruction of microbes. By enhancing endothelial antimicrobial function, PF4 represents a significant yet previously underrecognized host defense mechanism that limits bacterial spread and alleviates vascular injury during infection. KEY POINTSO_LIIn vitro, PF4 accelerates bacterial clearance by enhancing endothelial uptake of bacteria and promoting their trafficking to the lysosome. C_LIO_LIIn murine sepsis, PF4 augments pathogen clearance to reduce infection severity, limit organ injury, and improve survival. C_LI

cell biology↗

bioRxiv2025

Carbohydrate consumption drives adaptive mutations in Escherichia coli associated with increased risk for systemic infection

Dissemination of organisms from the gut microbiota is a major contributor to sepsis and critical illness. Patients with cirrhosis are prone to systemic infections and are commonly prescribed the carbohydrate lactulose to manage hepatic encephalopathy (HE) 1. Commensal metabolism of lactulose is believed to reduce pathobiont colonization through short-chain fatty acid production, but its direct effects on gut pathobionts remain unexplored 2. Here, we show that lactulose consumption unexpectedly selects for mutations in Escherichia coli lactose (lac) operon regulation, enhancing its metabolic fitness and colonization capacity. This is mediated by selection for constitutive expression of the lac operon through mutations in its regulatory components. Using in vitro systems, murine models, and clinical samples, we demonstrate that these mutations enable E. coli to exploit lactulose as a carbon source, bypassing host carbohydrate metabolism and increasing its intestinal colonization. Despite its long-standing use in HE treatment, we find that lactulose has a paradoxical association with risk of infection hospitalization in patients with cirrhosis in a large epidemiologic study. The emergence of lactulose-adapted E. coli strains could be suppressed by a dietary oligosaccharide that competitively inhibits lactulose uptake. These findings reveal a mechanism by which dietary substrates exert selective pressure on the microbiome, with implications for diet-based strategies to modulate microbial evolution and infection risk.

microbiology↗

bioRxiv2023

Colonization and Dissemination of Klebsiella pneumoniae is Dependent on Dietary Carbohydrates

Dysbiosis of the gut microbiota is increasingly appreciated as both a consequence and precipitant of human disease. The outgrowth of the bacterial family Enterobacteriaceae is a common feature of dysbiosis, including the human pathogen Klebsiella pneumoniae. Dietary interventions have proven efficacious in the resolution of dysbiosis, though the specific dietary components involved remain poorly defined. Based on a previous human diet study, we hypothesized that dietary nutrients serve as a key resource for the growth of bacteria found in dysbiosis. Through human sample testing, and ex-vivo, and in vivo modeling, we find that nitrogen is not a limiting resource for the growth of Enterobacteriaceae in the gut, contrary to previous studies. Instead, we identify dietary simple carbohydrates as critical in colonization of K. pneumoniae. We additionally find that dietary fiber is necessary for colonization resistance against K. pneumoniae, mediated by recovery of the commensal microbiota, and protecting the host against dissemination from the gut microbiota during colitis. Targeted dietary therapies based on these findings may offer a therapeutic strategy in susceptible patients with dysbiosis.

microbiology↗

bioRxiv2022

Bacterial cell widening alters periplasmic size and activates envelope stress responses

The Rcs signal transduction system is a phosphorelay responsible for sensing a wide variety of enterobacterial cell envelope stresses. In Escherichia coli, the Rcs system is required to survive A22 and mecillinam treatment, two drugs that perturb cell size. To test whether cell size changes might be correlated with envelope damage and thereby sensed by the Rcs system, we tuned E. coli cell size via drug inhibition with A22, point mutations to the cell-shape determinant MreB, and mechanically confined growth. In all conditions, cell width was strongly correlated with Rcs activation, with wider cells exhibiting more activation than wild-type. In all conditions, RcsF, the outer membrane-localized upstream component of the Rcs system, was essential for responding to cell width changes. Consistently, several envelope gene deletions known to induce the Rcs system via RcsF resulted in cells that were wider than wild-type. Cryo- electron microscopy revealed that the periplasm of a wide MreB mutant was on average [~]3 nm thinner than wild-type, thereby bringing RcsF closer to the downstream components of the signaling cascade in the inner membrane. Conversely, extending the flexible linker region of RcsF by [~]3 nm increased Rcs activity in wild-type cells. In summary, we propose that the Rcs system responds to changes in cell width because of altered periplasmic thickness.

microbiology↗

bioRxiv2020

Effects of regulatory network organization and environment on PmrD connector activity and polymyxin resistance in Klebsiella pneumoniae and Escherichia coli

Polymyxins are a class of cyclic peptides with antimicrobial activity against Gram-negative bacteria. Resistance to these compounds is often mediated by pathways that also confer resistance to host antimicrobial peptides. In Enterobacteriaceae, the PhoQ/PhoP and PmrB/PmrA two-component systems regulate many of the genes associated with these resistance mechanisms. In K. pneumoniae, spontaneous polymyxin resistance is frequently acquired through inactivation of the gene mgrB, which encodes a negative regulator of PhoQ. However, this resistance mechanism has not been reported in other genera of Enterobacteriaceae, despite the presence of mgrB among many members of this family. In addition, the frequency of developing spontaneous resistance to the antimicrobial peptide polymyxin through chromosomal mutations is much higher in Klebsiella compared to Salmonella or E. coli. Here we show that in K. pneumoniae, PmrD is not required for polymyxin resistance arising from inactivation of mgrB. In addition, we show that in E. coli, the protein PmrD can activate PmrA under certain conditions. Our results suggest that the importance of PmrD connector activity in polymyxin resistance depends on both the network organization and on the environmental conditions associated with PmrB stimulation.

microbiology↗

bioRxiv2018

Functional determinants of a small protein repressor controlling a broadly conserved bacterial sensor kinase

The PhoQ/PhoP two-component system plays a vital role in the regulation of Mg2+ homeostasis, resistance to acid and hyperosmotic stress, cationic antimicrobial peptides, and virulence in Escherichia coli, Salmonella and related bacteria. Previous studies have shown that MgrB, a 47 amino acid membrane protein that is part of the PhoQ/PhoP regulon, inhibits the histidine kinase PhoQ. MgrB is part of a negative feedback loop modulating this two-component system that prevents hyperactivation of PhoQ and may also provide an entry point for additional input signals for the PhoQ/PhoP pathway. To explore the mechanism of action of MgrB, we have analyzed the effects of point mutations, C-terminal truncations and transmembrane region swaps on MgrB activity. In contrast with two other known membrane protein regulators of histidine kinases in E. coli, we find that the MgrB TM region is necessary for PhoQ inhibition. Our results indicate that the TM region mediates interactions with PhoQ and that W20 is a key residue for PhoQ/MgrB complex formation. Additionally, mutations of the MgrB cytosolic region suggest that the two N-terminal lysines play an important role in regulating PhoQ activity. Alanine scanning mutagenesis of the periplasmic region of MgrB further indicates that, with the exception of a few highly conserved residues, most residues are not essential for MgrBs function as a PhoQ inhibitor. Our results indicate that the regulatory function of the small protein MgrB depends on distinct contributions from multiple residues spread across the protein. Interestingly, the TM region also appears to interact with other non-cognate histidine kinases in a bacterial two-hybrid assay, suggesting a potential route for evolving new small protein modulators of histidine kinases.

microbiology↗