Nickel and Ultraviolet Adaptation of Mesorhizobia
Abstract
Rhizobium soil bacteria participate in a mutualism with legumes species. The rhizobium exchange nitrogen fixed from the environment, for carbon sugars the host provides. Biotic conditions that affect this mutualism include growth-inhibiting heavy metals and exposure to ultraviolet radiation. Serpentine soil high in concentrations of heavy metals, such as nickel, tend to have low-density growth with short plants. Some legumes can thrive in nickel-rich serpentine soils where other plants cannot. This may be a result of local adaptation. If host survival is enhanced by their mutualistic rhizobia, then do strains in heavy metal rich environments with increased ultraviolet radiation have higher tolerance to nickel and ultraviolet radiation than those found elsewhere? To address this question, I tested the nickel and UV tolerance of 770 diverse strains of Mesorhizobium collected by Porter lab from hosts in Oregon and California. I used assays that consisted of plating strains on nutrient agar and exposing the bacteria to nickel and UV light treatments. The comparison between a strain’s nickel tolerance and the soil nickel concentration showed a statistically significant positive correlation. UV tolerance did not show a correlation with the soil chemistry. Interesting, nickel and UV tolerance have a significant positive linear correlation. I used a phylogenetic tree developed by sequencing 300 of this experiment’s strains to differentiate phylogenetic relatedness and local adaptation. Tolerant strains of rhizobia can be used to pick inoculum to use in bioremediation for heavy-metal polluted waste watered agricultural land.
About the Presenters
Christopher Dexheimer
Christopher Dexheimer is an undergraduate researcher in the Porter Lab. He is a first-generation college student who is seeking a B.S. in biology with minors in chemistry, molecular sciences, and statistics. Chris started in the Porter lab in the fall of 2018 and plans to graduate fall 2022. His scientific interests include molecular and macro ecology, natural resources and evolutionary biology with specific emphasis on symbiosis and mutualisms. When not in the lab, you can find him enjoying the outdoors of the pacific northwest.