Secondary Metabolites Produced by the Marine Bacterium Halobacillus salinus That Inhibit Quorum Sensing-Controlled Phenotypes in Gram-Negative Bacteria

Abstract

Certain bacteria use cell-to-cell chemical communication to coordinate community-wide phenotypic expression, including swarming motility, antibiotic biosynthesis, and biofilm production. Here we present a marine gram-positive bacterium that secretes secondary metabolites capable of quenching quorum sensing-controlled behaviors in several gram-negative reporter strains. Isolate C42, a Halobacillus salinus strain obtained from a sea grass sample, inhibits bioluminescence production by Vibrio harveyi in cocultivation experiments. With the use of bioassay-guided fractionation, two phenethylamide metabolites were identified as the active agents. The compounds additionally inhibit quorum sensing-regulated violacein biosynthesis by Chromobacterium violaceum CV026 and green fluorescent protein production by Escherichia coli JB525. Bacterial growth was unaffected at concentrations below 200 g/ml. Evidence is presented that these nontoxic metabolites may act as antagonists of bacterial quorum sensing by competing with N-acyl homoserine lactones for receptor binding.Taxonomically diverse marine bacteria have proven to be a rich resource for the discovery of structurally unique and bioactive secondary metabolites (5). Given the intense microbial competition for resources such as space and nutrients, it is probable that many excreted metabolites help mediate microbe-microbe interactions. Various antibiotics have been implicated as chemical defenses for marine bacteria, thus suggesting a role for the biosynthesis of toxic metabolites. For example, a pelagic Alteromonas species produces the antibiotic 2-n-pentyl-4-quinolinol, capable of influencing bacterial community structure on particles (25), and production of the antibiotic andrimid by a marine Vibrio species prevents colonization of surfaces by the particle specialist Vibrio cholerae (26).Though not yet widely studied, the secretion of nontoxic molecules could also play important roles in antagonistic marine microbial interactions. Quorum sensing pathways of competing bacteria are potential targets for such nontoxic chemical defenses. Bacterial communication is facilitated by the production and subsequent recognition of small signaling molecules (autoinducers) and can regulate important phenotypes, including bioluminescence, biofilm formation, swarming motility, antibiotic biosynthesis, and virulence factor production (3, 7, 15). Gram-negative bacteria commonly use N-acyl homoserine lactones (AHL) as signaling molecules, which bind their cognate receptor proteins to activate gene expression (10). These autoinducers share a conserved L-homoserine lactone moiety, and the length and sites of oxidation on the acyl chain dictate the species specificity (37). In contrast, gram-positive bacteria generally accomplish quorum sensing using posttranslationally modified peptides as autoinducers. For example, Staphylococcus aureus uses cyclic oligopeptides to regulate virulence factor production (11).Here we report the production of nontoxic secondary metabolites by a marine gram-pos...

Isolation of a broad spectrum antibiotic producer bacterium, Pseudoalteromonas piscicida PG-02, from the Persian Gulf

“…With respect to enormous biodiversity in the marine environment so that in the case of microorganisms, sea water is composed of 78 million microscopic cell per ounce or the bottom, which mimic the soil, contain more than 1 billion cells in the volume of an ordinary cube of sugar this environment as a rich resource can be exploited for developing new natural pharmaceutical products especially antibiotics . Furthermore, existence of a given the intense microbial competition for resources such as space and nutrients between marine bacteria especially those that inhabited in sediment introduce a powerful selection pressure that can cause excretion of metabolites by these microorganisms for help mediate microbe-microbe interaction that occur on the order of micrometers, it is likely that many of these metabolites were structurally unique and bioactive secondary metabolites (Teasdale et al, 2009;Balcazar et al, 2010). Rosnfeld and Zobell, in 1947, were reported the first document of antibiotic producing marine bacterium (McCarthy et al, 1994).…”

Exploiting Quorum Sensing To Confuse Bacterial Pathogens

“…Numerous reports are emerging that provide empirical data demonstrating QSI activity from various marine sources that include sponges (290), microalgae (291), bryozoa (292), and alga-and coral-associated bacteria (293,294). Low-micromolar concentrations of phenethylamide compounds from the marine bacterium Halobacillus salinus were found to inhibit V. harveyi luminescence and C. violaceum pigment production without inhibiting growth (295). Secondary metabolites isolated and purified from sponges (290) and Gram-negative cyanobacteria (296) also exemplify successes where low-micromolar concentrations of purified compounds could inhibit QS reporters.…”

Signaling-mediated cross-talk modulates swarming and biofilm formation in a coral pathogen Serratia marcescens

“…The ability of marine prokaryotes and eukaryotes to excrete compounds that stimulate or inhibit QS reporters is now well documented (Pasmore and Costerton, 2003;Wagner-Dobler et al, 2005;Skindersoe et al, 2008;Teasdale et al, 2009;Kwan et al, 2010); however, ecological roles of these compounds and of the bacteria that produce them are less understood. Therefore, our subsequent experiments focused on testing the behaviors of the isolates in the dual-species microbial consortia consisting of the coral pathogen S. marcescens PDL100 and the isolate of interest.…”