Glucose confers protection to Escherichia coli against contact killing by Vibrio cholerae

Abstract

Evolutionary arms races are broadly prevalent among organisms including bacteria, which have evolved defensive strategies against various attackers. A common microbial aggression mechanism is the type VI secretion system (T6SS), a contact-dependent bacterial weapon used to deliver toxic effector proteins into adjacent target cells. Sibling cells constitutively express immunity proteins that neutralize effectors. However, less is known about factors that protect non-sibling bacteria from T6SS attacks independently of cognate immunity proteins. In this study, we observe that human Escherichia coli commensal strains sensitive to T6SS attacks from Vibrio cholerae are protected when co-cultured with glucose. We confirm that glucose does not impair V. cholerae T6SS activity. Instead, we find that cells lacking the cAMP receptor protein (CRP), which regulates expression of hundreds of genes in response to glucose, survive significantly better against V. cholerae T6SS attacks even in the absence of glucose. Finally, we show that the glucose-mediated T6SS protection varies with different targets and killers. Our findings highlight the first example of an extracellular small molecule modulating a genetically controlled response for protection against T6SS attacks. This discovery may have major implications for microbial interactions during pathogen-host colonization and survival of bacteria in environmental communities.

High throughput identification of genes conferring resistance or sensitivity to toxic effectors delivered by the type VI secretion system

“…E. coli are commonly used as prey cells to measure the activity of T6SSs and we previously examined how specific gene knockouts can drastically reduce E. coli survival against the V. cholerae T6SS effectors, TseH and TseL (7, 8). Other groups have also identified genes that influence E. coli survival against T6SSs, including mutants in clpP or crp genes, which were resistant to the T6SS of Agrobacterium tumefaciens or V. cholerae , respectively (19, 29). Cumulatively, these works provide a set of genes with known roles in T6SS survival, which serve as positive controls for identifying important genes.…”

“…The metabolic state of the prey cell can also have a profound influence on survival: Stationary phase prey can be more susceptible to attacks due to their decreased ability to form microcolonies isolated from attackers, replace damaged components or produce sufficient immunity proteins for protection (7,11,12,(26)(27)(28). Finally, catabolite repression is another mechanism recently shown to influence E. coli survival against a T6SS attack, where growth with glucose or using mutant prey lacking the cAMP receptor protein (CRP) showed improved survival against the T6SS of Vibrio cholerae strain C6706 (29).…”

Modular Molecular Weaponry Plays a Key Role in Competition Within an Environmental Vibrio cholerae Population

“…On the other hand, the presence or absence of certain genes (such as the caseinolytic protease genes clpP and clpA , or the disulfide bond formation gene dsbA ) can also increase a strain’s susceptibility to T6SS attacks ( Lin et al, 2019 ; Mariano et al, 2019 ). Even the simple addition of glucose to the growth medium can have drastic effects on competition ( Crisan et al, 2021 ). As such, although an important component, E-I module composition alone is obviously not the sole deciding factor determining the outcome of T6SS-mediated competition, or competition as a whole.…”

A New Contact Killing Toxin Permeabilizes Cells and Belongs to a Broadly Distributed Protein Family

“…2C ). We recently reported that target E. coli cells are protected against T6SS attacks from strain C6706* when cocultured on LB medium supplemented with 0.4% glucose ( 4 ). By contrast, we observed that killer C6706*/pAux4 cells bypass the glucose-mediated resistance and efficiently eliminate E. coli cells when the coculture is performed on LB medium with glucose ( Fig.…”

“…Cells with an active T6SS (“killer cells” here) translocate toxic protein effectors into adjacent target cells. However, the outcome of T6SS-mediated aggression is influenced by the presence of immunity proteins in target cells, the external environment, and target cell stress responses ( 4 – 7 ). The harpoon-like proteinaceous apparatus is anchored to the membrane of killer cells by the membrane complex, which spans the inner membrane and periplasm ( 8 – 10 ).…”