Soil microbial invasions: Patterns, mechanisms, and impacts garnered from Escherichia coli invasions into soil

Microbial invasions come in many forms. They could manifest as infections we catch, probiotics we take, or natural expansions of microbes past their native territories. The patterns, process, and mechanisms controlling such invasions have until only recently remained elusive. In this thesis, we examine each of these aspects through synthesizing the most recent advances in microbial invasions, and this fusion serves as a foundation that drives our further questioning and experimentation. By using a model invasion system whereby Escherichia coli, the invader bacterium, is invaded into soil samples, we find that the biological diversity of the soil microbial community plays a major role in determining the invader’s fate. When the diversity of the soil microbial community is high, invasion is low—and when the diversity of the soil microbial community is low, invasion is high. Further experimentation indicates that more diverse communities use more of the soil’s resources than less diverse communities. This leaves little sustenance available for any invader, making the chance of a successful invasion slim. Yet, even when invasions are not successful, the mere attempt will impact the soil microbial community, causing the population size of some individuals to decrease and others to increase. This observation underscores the dynamic nature and complexity of microbial invasions. By applying the principles that diversity and resource availability determines an invader’s success, there is a promising avenue to improve the efficiency of many practical applications where microbial invasions must be controlled and calculated, such as biocontrol agents, biofertalizers, and probiotic treatments.