Characterization of medium chain length (R)-3-hydroxycarboxylic acids produced by Streptomyces sp. JM3 and the evaluation of their antimicrobial properties.

ABSTRACT

(R)-3-Hydroxycarboxylic acids, chiral enantiomers of bacterial polyhydroxyalkanoates (PHA), may be valuable synthons for the production of numerous industrial materials such as ß-lactams, fungicides, flavors, pheromones and vitamins. In this study, (R)-3-hydroxycarboxylic acid [(R)-3HAs)] synthons were produced by Streptomyces sp. JM3 (JN166713) under batch fermentation. Initial confirmation of PHA production was achieved by matrix assisted laser desorption ionization-time of flight mass spectroscopy and gas chromatography/mass spectroscopy (GC/MS). Subsequently, (R)-3HAs were produced by in vivo depolymerization and the monomers were separated using acid precipitation and anion exchange chromatography. The (R)-3HAs were identified by GC/MS as 3-trimethylsiloxy esters of decanoic, octanoic and butanoic acids. This was further supported by (13)C nuclear magnetic resonance spectrometry. The (R)-3HAs exhibited antimicrobial activity against Escherichia coli O157H7, Listeria monocytogenes (ATCC 7644) and Salmonella typhimurium (ATCC 14028) with minimum inhibitory concentration ranging from 12.5 to 25 mg ml(-1). However, the minimum bactericidal concentration data suggest that the (R)-3HAs may be bactericidal for E. coli O157H7 and bacteriostatic for S. typhimurium and L. monocytogenes. Furthermore, the major purified synthon was shown to minimize the invasion of fibroblasts by S. typhimurium (ATCC 14028) [p < 0.05], using the MTT assay [(3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide)].