Rapid niche shifts in bacteria following conditioning in novel soil environments

Realized niche breadth is generally expected to be smaller than fundamental niche breadth. For soil microorganisms, this is due in part to competition from co-occurring microbes, so removing competitors should allow for expanded use of resource and habitats (i.e. ecological release). We hypothesized that conditioning bacterial isolates to biotically cleared soils would allow for niche breadth expansion relative to ancestral bacteria, and that this niche expansion would be driven by habitat-dependent niche shifts between derived populations. We grew two taxonomically divergent bacteria for 3 months in four biotically cleared soils and a biotically cleared 'home' soil. We then assessed changes in the niche breadth and fitness (i.e. growth; respiration; carbon resource use) of conditioned bacteria. Post-conditioning, Pseudomonas populations showed the potential for increased growth rate in-culture and in-soil when conditioned to soils, and constrained resource use relative to the ancestral population, while Paenibacillus showed minimal changes in soil habitat breadth, but expanded resource use in conditioned populations. When introduced into complex novel environments containing reduced biotic pressure, soil bacteria can undergo rapid niche shifts, but this response varies across taxa and habitats. This suggests that species identity and habitat should interact to shape near-term niche shifts when microbes establish in new soil environments. Read the free Plain Language Summary for this article on the Journal blog.