Glucose promotes resistance of human commensalEscherichia coliagainst contact-killing by pandemicVibrio cholerae

Abstract

word count: 229 18 Text word count: 3540 19 20 21 22 23 24 25 26 27 28 2 ABSTRACT 29Evolutionary arms races among organisms are broadly prevalent and bacteria have evolved 30 defensive strategies against various attackers. A common microbial aggression mechanism is the 31 Type VI Secretion System (T6SS), a contact-dependent bacterial weapon used to deliver toxic 32 effector proteins into adjacent target cells. Sibling cells constitutively express immunity proteins 33 that neutralize effectors. However, less is known about mechanisms that allow non-sibling bacteria 34 to respond to external cues and survive T6SS attacks independently of immunity proteins. In this 35 study, we show that resistance to T6SS attacks is promoted by a genetically controlled response to 36 exogenous glucose. We observe that multiple human Escherichia coli commensal strains lacking 37 immunity proteins are sensitive to T6SS attacks from pandemic Vibrio cholerae on nutrient-rich 38 media. By contrast, E. coli cells become resistant to attacks when co-cultured on the same media 39 with glucose. We confirm that glucose does not impair V. cholerae T6SS activity. Instead, we find 40 that cAMP receptor protein (CRP), which alters expression of hundreds of genes in response to 41 glucose, controls resistance to T6SS attacks in E. coli cells. Consistent with the observed resistance 42 on media with glucose, an E. coli crp disruption mutant survives significantly better against V. 43 cholerae T6SS attacks even in the absence of glucose. Finally, we also show that resistance to 44 T6SS attacks depends on the pH of the medium and varies based on the target and killer strains. 45 IMPORTANCE 46Many Gram-negative bacteria, including important pathogens, encode T6SS genes to deliver toxic 47 effectors and eliminate competitors. Our results uncover a novel defense mechanism against T6SS 48 attacks that is triggered by an external stimulus and mediated by a metabolic response in non-kin 49 target cells. In microbiomes such as those in gastrointestinal tracts where T6SS activity is known 50 to occur, signaling by metabolites like glucose may affect the efficacy of T6SS attacks and alter 51 3 microbial community composition. Our findings could have vast implications for microbial 52 interactions during pathogen colonization of hosts and survival of bacterial cells in environmental 53 communities. Furthermore, the glucose-mediated resistance observed here might provide a novel 54 example of an evolutionary arms race between killer T6SS cells and target bacteria. 55 INTRODUCTION 56 Vibrio cholerae is the waterborne enteric pathogen that causes serious, often fatal cholera diarrheal 57 disease when ingested by humans. This ubiquitous microbe is found in dense polymicrobial marine 58 communities on chitinous surfaces and in animal reservoirs like fish or zooplankton (1-3). To 59 compete with other cells in densely-populated microbial environments, V. cholerae employs a 60 harpoon-like structure called the Type VI Secretion System (T6SS) (4-7). The T6SS pu...

A new contact killing toxin permeabilizes cells and belongs to a large protein family

“…2C). We recently reported that target E. coli cells are protected against T6SS attacks from strain C6706* when co-cultured on LB medium supplemented with 0.4% glucose (44). By contrast, we observe that killer C6706*/pAux4 can bypass the glucose-mediated resistance to efficiently eliminate E. coli cells even when the co-culture is performed on LB medium with glucose (Fig.…”

Two Type VI Secretion Systems in Vibrio coralliilyticus RE22Sm exhibit differential target specificity for bacteria prey and oyster larvae

“…The KO mutation of vcpR reduced antibacterial activity with target cell decline of 2.52 log compared to wild type RE22Sm causing E. coli Sm10 cell density to decline by 3.33 log, a reduction of ~0.8 log. While we do not know the reason for the difference between effects of the vcpR mutation on predation, we suggest that E. coli Sm10 is a more vulnerable prey target than V. cholerae, perhaps because V. cholerae contains a T6SS with immunity genes (40) and E. coli Sm10 does not (41).…”

Engineering a customizable antibacterial T6SS-based platform inVibrio natriegens

“…However, it remains to be determined whether the observed lack of toxicity against certain bacteria is a property of an effector's activity, the ability of the T6SS to deliver the effector into certain prey, the environmental conditions under which the competition took place, or a property of the prey that renders it resistant to the activity of certain effectors. Notably, natural resistance of bacteria against T6SS effector intoxication, which is not mediated by cognate immunity proteins, has been recently reported in other studies [42][43][44][45] . Therefore, our platform serves as a unique tool that allows T6SS-mediated secretion of single effectors under a wide range of environmental conditions, enabling one to study effector toxicity ranges and revealing natural resistance mechanisms and strategies.…”