Microbial Antibiotic Production in Cave Bacteria

Caves contain abundant Actinobacteria, which are valuable sources of novel antibiotics, replacing currently ineffective antibiotics. Our study explores secondary metabolites produced by cave and surface soil bacteria. Thirty-nine bacterial isolates from 229 m below the surface of Carlsbad Cavern and 19 surface soil bacterial isolates were inoculated onto Actinobacteria Isolation Agar (AIA), AIAFeMn, Bennett’s, Oatmeal, and RASS media. Cave cultures were incubated onsite for 24 hours, subsequently incubated in the lab at 15°C, and subcultured onto R2A to obtain pure isolates, which were characterized morphologically.  AIA was the most effective media in recovering cave isolates. Coloration (white vs. colored) exhibited among isolates was almost equal, except in cave pool isolates, which were overwhelmingly colored. Of the cultures yielding a clear Gram status, more soil organisms were Gram negative (70%), while more cave organisms were Gram positive (58%). Mucoid colony growth was only found among cave isolates. An agar diffusion test utilizing eight common pathogens was used to test pathogen inhibition by secondary metabolite production. Fifteen percent of the initial isolates tested for antibiotic production, appeared to inhibit pathogen growth.  Of the 15% that showed inhibition, >50% were colored and glistening in morphology, while Gram stains yielded equal representation for positive and negative.  These experiments will provide insight into the special properties of cave-adapted bacteria and help delineate their potential for antibiotic synthesis. Results from these tests will identify a core set of isolates in which we will explore genes and secondary metabolite pathways associated with antibiotic production.