Collaborative Research: Ammonia oxidizers and their heterotrophic friends

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Microorganisms play a major role in the global nitrogen cycle. One group of bacteria, ammonia oxidizing bacteria, oxidize ammonium to nitrite and thus play a key role in the removal of ammonium from human derived urea in wastewater treatment plants. In nature, diverse microorganisms coexist and interact in complex ways. Communities of different microorganisms can perform vital functions more efficiently than single species achieve alone. Ammonia oxidizing bacteria are one example, where ammonia is converted more efficiently when in a microbial community than when the oxidizing bacteria are alone. Yet, the interactions among microbial neighbors that improve ammonia conversion are not well understood. The goal of this project is to better understand how living in microbial communities improves ammonia oxidizing bacteria's ability to convert ammonia. An additional goal of this project is to educate a diverse group of students on the importance of microbial communities, and to raise awareness and urgency about water quality. Graduate and undergraduate students will be trained in state of the art microbiology techniques and involved in the research. Elementary school students from rural Ohio and undergraduate non-microbiology majors will be taught about the importance of microbial communities, nitrification, and water quality. This research will provide important insight into synergistic interactions within bacterial communities and increase the ability to manipulate microbial communities for improved or desired function, such as those in wastewater plants to improve ammonia removal.Ammonia-oxidizing bacteria (AOB) oxidize ammonia to nitrite. AOB are core contributors to nitrification, a crucial step in the global nitrogen cycle. As part of microbial communities, AOB positively interact with nitrite-oxidizing bacteria and heterotrophic bacteria. It has already been shown that the nitrite-oxidizing bacteria keep the level of toxic nitrite around AOB low, maintaining a beneficial environment that allows for AOB growth. The mechanisms underlying the positive interactions of AOB with heterotrophic bacteria have not been elucidated. These positive interactions will be investigated in well-defined laboratory co-cultures, enrichment cultures, and native environments. Experiments will include (1) proteome and transcriptome analysis of the AOB Nitrosomonas sp. Is79 in the presence of heterotrophic bacteria as single and mixed cultures; (2) proteome analysis of three additional AOB strains in the presence of heterotrophic bacteria; and (3) proteome analysis of an AOB incubated in their original environment. The results will be analyzed to identify strain-specific physiological responses in order to determine the nature of the interactions between AOB and heterotrophic bacteria. Insights into the molecular mechanisms and metabolic pathways in AOB that are impacted by heterotrophic bacteria will add to the growing field of research on autotrophic-heterotrophic interactions. This research will also address the physiological similarities and differences in AOB grown in laboratory pure cultures, in laboratory enrichment cultures, and in their original environments.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.