We are examining the systems-level effects of multiple metal exposure in microorganisms. While many studies have explored the impacts of individual metals on bacterial physiology, multiple metals will frequently co-exist at elevated levels in contaminated sites.  Using a native Bacillus cereus isolate from a contaminated site, we have found that  metals in combination impact cell physiology in a manner that could not have been predicted from summing phenotypic responses to the individual metals. Exposure to this metal mixture induced a global iron starvation response not observed during exposure to the individual metals. Disruption of iron homeostasis decreased the activity of iron-cofactor-containing enzymes that are critical for cellular metabolism. 

Moving forward, we are further dissecting the mechanisms through which metals interact within microbial systems using model organisms. In particular, we are interested in examining how mixed metal and other mixed waste exposure impacts the carbon metabolism of animal intestinal microbiota. 

Model for decreased nitrate/nitrite reductase activity during mixed metal exposure. Goff, J.L. et al. Mixed heavy metal stress induces global iron starvation response. ISME J 17, 382–392 (2023). 

We are exploring how how mobile genetic elements (MGEs) shape microbial genome evolution in the ORR subsurface. Movement of MGEs by horizontal gene transfer (HGT) can promote the rapid adaptation of microorganisms to environmental stressors through analysis of both metagenome-assembled MGEs as well as MGEs in the genomes of pure culture isolates from contaminated environments.  Additionally, we are using adaptive laboratory evolution (ALE) to experimentally probe mechanisms of genome evolution during environmental stress.  In particular, we are interested in plasmid gene content and stability and the expansion of transposable elements in microbial genomes.  

Plasmids identified in the genome of an isolated representative of a dominant species in a mixed waste contaminated subsurface environment. Goff, J.L. et al. (2022) Ecophysiological and genomic analyses of a representative isolate of highly abundant Bacillus cereus strains in contaminated subsurface sediments. Environmental Microbiology, 24( 11), 5546– 5560.