Theses and Dissertations Collection

Methylobacterium is a diverse and dominant genus in the phyllosphere, having influence on plant fitness. However no allelopathic interactions have been defined for Methylobacterium that could influence community structure, though allelopathy is ubiquitous across microbial communities (Simons et. al., 2012; Majeed et. al., 2013). This study presents the discovery of a novel hemolysin-type bacteriocin, methylolysin A, produced by six Methylobacterium extorquens strains isolated from a single, natural community on soybean leaves. Methylolysin was shown to cause growth inhibition of sensitive strains by spot assays on dilute lawns of sensitive strains. Liquid growth assays of sensitive strains in the presence of the toxin also displayed this effect with significant growth inhibition, revealing a secreted toxin. Protease sensitivity assays that this secreted toxin is a protein. A characteristic virulence plasmid carrying a canonical hemolysin operon was uncovered through in silico analyses, and the annotation of the hemolytic genes carried on the plasmids were corroborated by SDS-PAGE size analysis and MALDI-TOF mass spectrometry spectra alignments. This study presents a novel hemolysin-type bacteriocin produced and secreted by Methylobacterium extorquens, and is the first initial step in understanding how this allelopathic interaction could potentially influence community structuring in an important ecological niche.