Characterisation of an antimicrobial producer isolated from the surface of seaweed

Abstract

During a screening of seaweed associated marine micro organisms, for their ability to produce antimicrobial compounds, an organism was isolated, producing antibacterial metabolite(s) and was found to be active against gram positive pathogens, multi-drug resistant pathogenic bacteria, and food borne spoilage fungi. The strain was identified as a gram-negative, short rod, which produced red-pigmented colonies and proved to be both catalase and oxidase positive. Ribotyping, indicated that this strain demonstrated a high sequence identity (99%) to Serratia plymuthica. Tests with a type strain of Serratia plymuthica, revealed that the strain did not produce a similar spectrum of antimicrobial activity. Preliminary characterisation of the inhibitory molecule(s) produced by this marine isolate, demonstrated that it was heat stable, low molecular weight, with pH resistant compound(s). Moreover, the activity was unaffected by prolonged incubation with enzymes such as Proteinase K. Transposon, mutagenesis was utilised, in an attempt to identify the genes involved, in antimicrobial production, to hopefully gain an insight into the nature of the antimicrobial compound. Fourteen mutants, unable to produce antimicrobial compound(s) were isolated, and the preliminary sequence analysis of three of the mutants, highlighted that they had transposon insertions within gene(s) homologous to polyketide synthase. Size exclusion chromatography (Gel filtration) was utilised in an attempt to purify and characterise the antimicrobial compound(s).