Phenotypic and genetic differences among marine Streptomyces communities from the Lower Laguna Madre

Background/Question/Methods

The research objective was to phenotypically and genetically characterize marine Streptomyces from the Lower Laguna Madre (LLM), a hypersaline estuary. We hypothesize spatial differences in abiotic and biotic factors will result in local adaptation of Streptomyces communities. One hundred and thirty five Streptomyces strains were isolated from three different sites (45 isolates per site) in the LLM designated SB, LMT051, and ABC. These strains were grown at varying salt and pH concentrations on starch casein agar to determine their tolerance levels to these environmental variables. In addition, 45 strains (15 per site) were chosen at random for further testing using  BIOLOG^TM microplates. 

Results/Conclusions

Salt concentrations at specific sites affected density and niche of the microorganisms present. Site SB had significantly more total bacteria but slightly less Streptomyces than the other 2 sites. All isolates could grow at 0, 15, and 30 ppt NaCl and one strain was able to grow at 60 ppt of NaCl. Salinity in the LLM has been noted to be as high as 80 ppt.  Optimally these Streptomyces isolates grew at pH 7.5 to 8.0. From the BIOLOG^TM data, mean number of utilized substrates and total activity for the isolates were determined. Based on these measures, isolates were grouped into 4 categories: those which could use many substrates and displayed high activity (Group 1), those which could use a few substrates and displayed high activity (Group 2), those which could use many substrates and displayed low activity (Group 3), and those which could use a few substrates and displayed low activity (Group 4). In general, isolates from SB were clustered in Groups 1 and 4; isolates from LMT051 were generally in Group 1 and isolates from ABC were mostly in Groups 2 and 4. Only a handful of isolates could be placed in Group 3 suggesting that this mode of nutrient utilization (the ability to use many substrates but with low activity) is not a common strategy of marine Streptomyces isolates from the LLM.  PCR experiments using a set of Streptomyces-specific primers resulted in the successful amplification of the 16S rRNA from 12 strains. These PCR products were sequenced to identify specific Streptomyces strains present in the LLM.