Soil bacteria adapt to tolerate heavy metal stress in their local soil environment
Abstract
Bacteria comprise the most diverse domain of life on Earth, including an uncountable number of species. Explaining why bacteria are immensely diverse has been a long-standing question in biology, with implications for conservation and resource management. The current model explaining this diversity includes two main steps. First, bacterial diversity is generated when bacterial populations adapt to their local soil environment, which eventually leads to speciation. Second, once bacterial species are generated, trade-offs between growth in different environments allow them to coexist. In other words, bacterial species that grow well in one environment do not grow well in others, preventing a single dominant species from driving all other species to extinction. This model is rarely tested, however, and we aimed to test both parts by studying soil bacteria in the genus Mesorhizobium. Certain Mesorhizobium populations have evolved tolerance to nickel, a toxic heavy metal, allowing them to survive in locally nickel-rich soils. We isolated 232 strains of Mesorhizobium from a wide range of soils and measured their growth under both high and low nickel conditions. We found that more nickel tolerant strains of Mesorhizobium tend to live in more nickel-rich soils. However, we did not observe a negative correlation between nickel tolerance and growth rate in the absence of nickel. In other words, we found evidence for local adaptation to soil environments, but no evidence for trade-offs in growth between soil environments. Mechanisms other than tradeoffs, or trade-offs involving different traits, may be more important for maintaining natural bacterial diversity.
About the Presenter
Miles Roberts
Miles Roberts has been conducting undergraduate research for the past two years under the mentorship of Dr. Stephanie Porter. His studies have mostly focused on the evolutionary ecology of soil bacteria, but he also has passions for mathematical modeling and genetics. Miles is close to earning a bachelor’s degree in biology with minors in chemistry and mathematics. After graduation, he will attend graduate school at Michigan State University where he will pursue a PhD in Genetics and Genome Sciences with a second major in Computational Plant Sciences. On the cat-to-dog person spectrum, Miles is definitely a cat person.