A rhodanese-like protein is highly overrepresented in the mutant S. clavuligerus oppA2::aph: effect on holomycin and other secondary metabolites production

A protein highly overrepresented in the proteome of Streptomyces clavuligerus oppA2::aph was characterized by MS/MS as a rhodanese-like enzyme. The rhlA gene, encoding this protein, was deleted from strains S. clavuligerus ATCC 27064 and S. clavuligerus oppA2:: aph to characterized the RhlA enzyme activity, growth on different sulfur sources and antibiotic production by the mutants. Whereas total thiosulfate sulfurtransferase activity in cell extracts was not affected by the rhlA deletion, growth, cephamycin C and clavulanic acid production were impaired in the rhlA mutants. Holomycin production was drastically reduced (66-90%) in the rhlA mutants even when using S. clavuligerus Delta rhlA pregrown cells, suggesting that this enzyme might be involved in the formation of the cysteine precursor for this sulfur-containing antibiotic. While growth on thiosulfate as the sole sulfur source was particularly low the volumetric and specific antibiotic production of the three antibiotics increased in all the strains in the presence of thiosulfate. This stimulatory effect of thiosulfate on antibiotic production was confirmed by addition of thiosulfate to pre-grown cells and appears to be a general effect of thiosulfate on oxidative stress as was also evident in the production of staurosporin by S. clavuligerus.