Screening environmental bacteria for naturally occurring antibiosis: identifying producers and their compounds

Julie Bruening


The rapidly escalating problem of antibiotic-resistant bacterial pathogens threatens to limit the clinical treatment of infectious disease, as many bacteria have evolved resistance to overprescribed and improperly used antibiotics. Alarmingly, the rate of increasing resistance far exceeds the current rate of development for new treatments. One solution to this problem may, quite literally, lie at our feet. Soil bacteria are recognized as one of the richest sources of naturally produced antibiotic compounds and produce many antibiotics currently in clinical use. In the current study, bacterial strains are cultured from various plant-, rhizosphere- and aquatic- environments throughout Western North Carolina and screened for antibiotic production using a high-throughput antagonism assay against Staphylococcus aureus and Escherichia coli. Within natural soil, microbes exist in complex, mixed-species communities, and recent research revealed that interspecies communication and competition may drive antibiotic production. Thus, we additionally screened bacterial co-cultures—pairwise combinations of soil bacteria—to activate cryptic biosynthetic gene clusters and enhance chemical diversity for drug discovery. To date, 184 bacterial isolates have been isolated, purified, and screened for antibiotic production with 9% exhibiting antibacterial activity against either a Gram-positive or Gram-negative bacterial agent. Bacteria not capable of antibiotic production in pure culture were tested in pairwise combinations for induced antibiotic production. We tested a total of 3,292 possible co-cultures and found several combinations of interest. However, we were unable to replicate the results in follow-up testing. Additional characterization of isolates of interest included 16S rDNA sequencing for phylogenetic identification, as well as an examination of  soil properties that may have influenced our findings.


bacteria, co-culture, antibiotics

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