Chlamydomonas reinhardtii Secretes Compounds That Mimic Bacterial Signals and Interfere with Quorum Sensing Regulation in Bacteria

Abstract

The unicellular soil-freshwater alga Chlamydomonas reinhardtii was found to secrete substances that mimic the activity of the N-acyl-l-homoserine lactone (AHL) signal molecules used by many bacteria for quorum sensing regulation of gene expression. More than a dozen chemically separable but unidentified substances capable of specifically stimulating the LasR or CepR but not the LuxR, AhyR, or CviR AHL bacterial quorum sensing reporter strains were detected in ethyl acetate extracts of C. reinhardtii culture filtrates. Colonies of C. reinhardtii and Chlorella spp. stimulated quorum sensing-dependent luminescence in Vibrio harveyi, indicating that these algae may produce compounds that affect the AI-2 furanosyl borate diester-mediated quorum sensing system of Vibrio spp. Treatment of the soil bacterium Sinorhizobium meliloti with a partially purified LasR mimic from C. reinhardtii affected the accumulation of 16 of the 25 proteins that were altered in response to the bacterium's own AHL signals, providing evidence that the algal mimic affected quorum sensing-regulated functions in this wild-type bacterium. Peptide mass fingerprinting identified 32 proteins affected by the bacterium's AHLs or the purified algal mimic, including GroEL chaperonins, the nitrogen regulatory protein PII, and a GTP-binding protein. The algal mimic was able to cancel the stimulatory effects of bacterial AHLs on the accumulation of seven of these proteins, providing evidence that the secretion of AHL mimics by the alga could be effective in disruption of quorum sensing in naturally encountered bacteria.

Future research trends in the major chemical language of bacteria

“…Several plant species secrete AHL mimics which can either stimulate or inhibit bacterial AHL QS systems (Bauer and Mathesius, 2004). Detection of AHL mimics have been reported in secretions of pea, rice, soyabean, tomato, crown vetch, M. truncatula, and from the unicellular algae Chlamydomonas reinhardtii (Degrassi et al, 2007;Gao et al, 2003;Teplitski et al, 2004;Teplitski et al, 2000). No evidence is currently available that these AHL mimics are interacting with QS systems in vivo; experiments in tomato with A. tumefaciens, in fact, have evidenced that these mimics cannot act as AHL agonists (Khan and Farrand, 2008).…”

Exploiting Quorum Sensing To Confuse Bacterial Pathogens

“…Plants have served as excellent systems in which to study microbe-microbe and interkingdom interactions. Plants produce compounds that serve as both autoinducer agonists and antagonists (260,261), and dozens of plant molecules, whose production profiles are found to change with the developmental stage of the plant, have been isolated and cataloged for their potential to interfere with bacterial signaling (262). For example, exudates from alfalfa seeds (Medicago spp.)…”

Regulation of microbial populations by coral surface mucus and mucus-associated bacteria

“…This result illustrates that a component universal to coral mucus, independent of species, location, and season, is capable of inhibiting pigment and antibiotic production associated with VBR7. The production of cell signaling molecules by many microbes regulates bacterial processes in a population density-dependent manner (Miller & Bassler 2001, Teplitski et al 2004). This type of communication, called 'quorum sensing,' is common in bacterial biofilms and regulates processes such as adhesion, antibiotic production, and virulence (Miller & Bassler 2001).…”