BIOCHEMICAL, NUTRIENT AND INHIBITORY CHARACTERISTICS OF STREPTOMYCES CULTURED FROM A HYPERSALINE ESTUARY, THE LAGUNA MADRE (TEXAS)

Abstract

Streptomyces are common soil bacteria that produce secondary metabolites, including several antibiotics; however, the characteristics of marine Streptomyces are largely unknown. Sediment samples were taken from 3 sites in the Laguna Madre to isolate marine Streptomyces. Sediment was diluted, spread onto synthetic seawater media to estimate the total bacterial density of the samples and spread onto starch casein agar to isolate Streptomyces. Isolated Streptomyces were tested for salinity tolerance and optimal growth pH. Isolates were assayed using API 20E^® test strips and BIOLOG^™ plates to construct biochemical profiles and assess nutrient utilization abilities of the bacteria, respectively. Individual Streptomyces were tested for the ability to inhibit the growth of other isolated Streptomyces (i.e., interference competition) and putatively identified by DNA sequencing. Results showed that there was no significant difference in microbial density in sediments from the 3 sampling sites. Eleven (11) Streptomyces pure cultures were obtained in total; most tolerated salinity up to 60 ppt and grew optimally at pH 7.5. Biochemical profile comparisons showed that the Streptomyces were only at least 74% similar; most (8/11) were >90% similar. Isolates could use between 87-95 carbon sources. Three (3) isolates displayed interference toward other isolates. Ten (10) isolates were identified as Streptomyces griseus by DNA sequencing. Laguna Madre Streptomyces organisms display some diverse characteristics with regards to their halotolerance, biochemical profiles, carbon source utilization and inhibition toward other organisms. Further investigations may yield greater understanding of these organisms in this and other marine environments and may be a reservoir of novel microorganisms and secondary metabolites.