A novel marine Bacillus with multiple amino acid analog resistance and selenomethionine-dependent antibiotic productivity.

Amino acid analogs (AAA) were used as selective pressures for isolation of marine bacteria with novel physiological properties and as effecters for antibiotic production. Relatively small numbers of isolates were obtained from a minimal medium containing aminoethylcysteine (AC), 3,4-dehydroproline (DP), 5-methyltryptophan (MT), and selenomethionine (SM). These bacteria exhibited a high probability (68%) of antibiotic production in the presence of AAA, which was 10-fold higher than that (7%) in the absence of AAA. Among them, strain 14, obtained as the only SM-resistant and SM-dependent antibiotic (selenohomocystine) producer, was characterized for microbiological properties. It showed taxonomic properties falling into those of the genus Bacillus, required seawater for growth, and exhibited a high level (0.5 mM) of resistance to all the AAAs tested. Neither known Bacillus spp. nor other marine isolates showed such properties. Therefore, the strain 14 appears to be the first marine Bacillus strain with unique AAA resistance and AAA-dependent antibiotic productivity. The AAA-resistance-based strategy was thus demonstrated to be effective for isolation of novel bacteria as well as for screening for antibiotic production.