Microbial responses to multiple environmental factors

My thesis addresses the question of how multiple environmental factors affect microorganisms, at the community, population and transcriptomic levels. I first explored how multiple environmental variables are correlated with microbial community patterns across the nearshore to offshore gradient in the coastal ocean. This study revealed clustering by sampling sites with distinct nearshore, continental shelf and offshore microbiomes. To investiage this phenomenon further, I used Bayesian modeling to reveal distinct taxa relationships with water temperature and distance from shore (a proxy for productivity and nutrients, among other environmental factors): some phylotypes are related to temperature, others to distance from shore and some to both factors. I next examined the influence of historical contingencies (prior environmental conditions) on microbial responses to factorial manipulation of pH (-0.3) and temperature (+ 3 oC) of microbes from our nearshore station (more variable environment) and the farthest offshore station (less variable). While at both stations, warming significantly altered microbial community composition, acidification alone had a minor influence. Compared with nearshore microorganisms, offshore communities exhibited larger changes in composition, taxa abundances, respiration rates and metatranscriptomes, suggesting increased sensitivity of microorganisms from the less variable environment to warming. Finally, I examined potential interactions between nanoparticles and nutrients using wetland manipulation experiments. This study showed the effect of nanoparticles on microbes was strongly dependent on interactions with other components of the system. The addition of the floating plant Egeria densa alone was sufficient to alter the microbiome’s response to nanoparticles, highlighting the importance of biological interactions when predicting microbial responses to environmental changes. This work will improve our understanding of short-term responses of microbial communities to multiple co-occurring environmental changes and help inform climate change and ecosystem models.