Secondary metabolite production by Streptomycetes in situ and in vivo

Streptomycetes are ubiquitous soil-dwelling saprophytes known to produce secondary metabolites, many of which are antibiotics. Secondary metabolism is usually a late growth phase event, brought on by different signals, e.g., nutrient starvation, environmental signals. In order to test whether in situ incubation changes the repertoire of expressed secondary metabolites (mainly antibiotics) compared to lab conditions, isolated Streptomyces sp. were embedded in AGSAgarose medium casted in tubes and incubated in either soil or sterile petri dishes. Results show significant differences between soil and sterile petri dish incubations, based on TLC results. No antibiotic activity was found (with E.coli as an indicator strain). However, over 15 (conservative estimation) different spots were observed in 10 different isolates, these could be either antibiotics (to which E.coli is resistant) or other secondary metabolites. This research shows that in situ incubation have the potential of bringing forth cryptic compounds that are ecologically important as well as new antibiotics.