Soils are reservoirs of antibiotic resistance. A variety of soil dwelling bacteria naturally synthesize antibiotics, and many of these antibiotic producers are also capable of sporulation. Two notable classes exhibiting both abilities are Actinobacteria, whose members synthesize more than half of all known antibiotics, and Bacilli known to produce particularly durable endospores. Presence of antibiotics selects for the proliferation of antibiotic resistance genes (ARGs). Spores are dormant and durable cell morphologies that are typically more resistant to environmental insults than vegetative cells. Wildfires are a source of environmental insults, including heat. It is hypothesized that a fire may select for spore forming antibiotic producers, given the fire is not intense enough to sterilize the soil. The objective of the present study is to screen for an interaction between fire intensity and antibiotic resistance. In June/July 2018, a wildfire produced areas of varying disturbance (stand-replacing fire, understory fire, no fire) within a subalpine lodgepole pine forest in southeastern Wyoming. In July 2019 soil samples were obtained from each of the areas and shotgun sequencing (classical metagenomics) was performed. ARGs were identified using double index alignment of next-generation sequence data (DIAMOND). Microbial composition was derived from the sequence data using Centrifuge (a novel microbial classification engine).
Results/Conclusions
130 different ARGs were identified in the understory fire (UF) site. No ARGs were identified in either the stand-replacing fire (SF) or no fire (NF) sites. Actinobacteria were least abundant in UF, while Bacilli were most abundant in UF. Penicillin producing Penicillium were least abundant in UF. Proliferation of ARGs in UF may be the cause of low antibiotic producer abundance. Despite our results, we suspect that ARGs are present in SF and NF albeit at lower levels than UF; the ARGs may have been too scarce to be captured in the soil sample, or if sampled, too scarce to be identified by DIAMOND. Further investigation into ARG and microbial community composition in this site is set to take place over the next year. The study of environmental antibiotic resistance enhances our understanding of clinical and agricultural resistance, as well as soil microbial community dynamics. Characterization of the microbial community response to fire may further elucidate microbial community responses to selective pressures and environmental disturbances.