Department of Biology

The artwork of an Indiana University biologist was selected as the cover image of the July 2020 issue of the American Society for Microbiology's Applied and Environmental Microbiology journal.

Jake McKinlay, an associate professor in the IU College of Arts and Sciences Department of Biology, helps his students—and now others—understand microbial physiology through the colorful artwork he creates.

"We had previously engineered a cooperative partnership between two bacteria, Escherichia coli and Rhodopseudomonas palustris. By our own design, the mutualism is based on the bidirectional exchange of essential carbon and nitrogen in the form of organic acids and ammonium," says McKinlay, "Thus, when we applied a genome-wide screen to identify genes important for mutualistic growth, were surprised to discover additional purine nucleotide cross-feeding from R. palustris to E. coli. E. coli mutants that could not synthesize purines, called purine auxotrophs, survived in the presence of R. palustris, but not when R. palustris was absent."

McKinlay's graphic on the AEM journal cover is an analogy for the discovery of unexpected purine cross-feeding from R. palustris to E. coli through transposon sequencing in a mutualistic coculture, as captioned in AEM, "Among a library of E. coli transposon mutants, struggling to stay afloat in a tumultuous sea, an E. coli purine auxotroph is rescued by a purine life ring excreted by the solar-powered vessel, R. palustris."

"Results from our study," explains McKinlay, "contribute knowledge on the genetic foundation of a microbial cross-feeding interaction and highlight that unanticipated interactions can occur even within engineered microbial communities."

A lichen is an example of a microbial cross-feeding interaction. Although sometimes plantlike in appearance and mistaken for a moss, a lichen is not a plant, but is rather a composite organism made up algae or cyanobacteria living symbiotically among fungal filaments. The crustlike or branching growth of lichens can often be found on tree trunks. Most microbial cross-feeding interactions, however, are not as visible or well known to the general population as lichens.

Cross-feeding also occurs between microbes in our gut and likely even affects our body mass index. Cross-feeding microbes also play a part in the production of some foods—cheese, for instance. And, they also affect our climate. The carbon cycle depicted in many textbooks is ultimately the sum of diverse microbial—and non-microbial—cross-feeding interactions.

"Microbial communities impact life on Earth in profound ways," says McKinlay, senior author of the cover image article. "They drive global nutrient cycles and influence human health and disease. These community functions depend on the interactions that resident microbes have with the environment and each other. Thus, identifying genes that influence these interactions will aid the management of natural communities and the use of microbial consortia as biotechnology."

Additional authors on the study are Breah LaSarre, (former NRSA postdoctoral fellow in the McKinlay lab), Adam M. Deutschbauer (deputy director of biotechnology development at the Lawrence Berkeley National Lab and adjunct professor of plant and microbial biology at the University of California, Berkeley), Crystal E. Love (postdoctoral fellow in the McKinlay lab). The study was supported by the U.S. Army Research Office grant W911NF-14-1-0411.