When do phages shape microbial communities? Assessing how changes in abiotic and biotic conditions impact the importance of phage

Bacteriophage - viruses that infect bacteria - are the most abundant life-forms on Earth, and are thought to be important in controlling microbial communities and - through this control - key ecosystem functions such as carbon and nutrient cycling and preventing bacterial disease. However, the evidence of the role phage plays in microbial communities remains mixed, is mainly correlational, varies between environments, and is almost non-existent in soil. The overarching aim of this project is to better understand the ecological conditions under which phage exert control on microbial communities. This is essential to understanding how microbial communities - and their associated
functions - will respond to environmental change.
I predict that phage impact on microbial communities will be strongest under conditions that maximise encounter rates between susceptible bacteria and phage. For example, during algal blooms and cholera epidemics - textbook examples of phage control - phage infections cause sudden reductions in the density of susceptible hosts
and increase the diversity of the bacterial community. In contrast, the increased bacterial and phage diversity and spatial structure of soil microbial communities likely result in reduced encounter rates, which may mean phages have a lower impact in soils. Furthermore, microbial communities may be less impacted by phages if all bacterial taxa can be affected by phages simultaneously. To complicate things further, soil conditions drastically change through time and space, thereby likely altering encounter rates and the impact of phages on soil communities. For example, we predict that phage impose stronger control in warmer and wetter soils where encounter rates are typically higher. Temperature and soil moisture are also two key factors that are likely to become more extreme and variable with climate change both globally and in the UK.
To properly investigate the causal impact of phage, I will dis-assemble and then...