First characterization of the cell-cell communication system in the facultative methylotrophic bacterium Methylobacterium extorquens AM1

C. G. NIETO PEÑALVER, F. CANTET, D. MORIN, O. SAUREL, A. MILON, J. VORHOLT

Canada

Conferencia; ASM 2nd conference. Cell-cell Communication in Bacteria; 2004

American Society for Microbiology

Methylobacterium strains are pink-pigmented facultative methylotrophic a-proteobacteria that are capable of growth in the presence of one-carbon compounds, e.g. methanol, but are also able to grow on a limited number of C2, C3, and C4 compounds, e.g. succinate. These strictly aerobic bacteria commonly colonize the leaves of plants and were found on the surfaces of all plants analysed so far  and might even represent the dominant phyllospheric bacterial population. The strain M. extorquens AM1 is the most well-studied representative of this group and object of our current investigation on the production of Quorum Sensing (QS) signals. In extracts of spent minimal medium supplemented with methanol as sole carbon source, eight molecules, that belong to the family of acyl homoserine lactone (acyl-HSL), were identified with different bioassays and a liquid chromatography–electrospray ionization ion trap MS–MS (LC–MS–MS) one-step method, being N-octanoyl-L-HSL the most abundant. Two C14-HSL with one and two double bonds, respectively, were also detected and the localisation of their exact positions is currently under investigation. Using minimal medium with succinate as sole carbon source, the QS signals were produced but were subjected to lactonolysis at least in part due to alcalization of the medium during sustained growth. This was shown by the application of a second buffer system to the culture medium that let to the detection of the produced signals also during late stationary phase. In parallel to the bioanalytic study of culture supernatants, the genome sequence of M. extorquens AM1 (http://www.integratedgenomics.com/genomereleases. html#list6) was analysed for the presence of lux-homologs. The genome sequence reveals the presence of three distinct luxI- and three luxR-homologs, two of them being arranged next to each other. First experiments with single, double, and triple luxI-mutants indicate a hierarchical system for acyl-HSL production in this strain.