journals.asm.org
Reciprocal cross-feeding between bacteria can limit the emergence of metabolic dependencies | Applied and Environmental Microbiology
Bacteria commonly engage in cross-feeding, where nutrients are transferred between neighbors. Cross-feeding is thought to alleviate energy expenditures for genes whose role can be met by cross-fed nutrients, leading to eventual gene loss. However, few examples have been documented, especially in comparison to monocultures that lack a cross-feeding partner. We grew cocultures pairing phototrophic Rhodopseudomonas palustris with fermentative Escherichia coli alongside corresponding monocultures for 650–800 generations. While coculture conditions required obligate exchange of nitrogen and carbon, additional cross-feeding of adenine and iron likely occurred. Contrary to expectations, dependencies for iron and unknown compounds emerged in monocultures, but expected iron and adenine dependencies were not observed in cocultures. Low expression of iron scavenging and adenine synthesis genes in cocultures suggested that cross-feeding repressed expression, thereby lowering gene cost. Thus, although cross-feeding can sometimes make costly genes dispensable, there are also cases where cross-feeding lowers gene cost, thereby promoting gene retention.
