Microbes are the most abundant organisms on Earth and play an important role as degraders, cycling nutrients in the environment. Too many or too few bacteria may disrupt a sensitive ecological balance and proper functioning of environmental processes such as carbon, nitrogen and phosphorus cycles. The abundance of bacteria populations in any given environment is controlled by various biological, chemical and physical mechanisms. Among the biological agents are microscopic predators, or micropredators, of bacteria. The most studied of these are protists, viruses that infect bacteria, and a group of bacteria collectively known as the Bdellovibrio and like organisms (BALOs). These micropredators prey upon certain bacteria to obtain required nutrients or other cellular material for their replication. In the process, cellular products from the prey bacteria are released into the environment and utilized as nutrients by other microbes. Although the micropredators co-occur, and likely interact, in nature, most experimental studies have investigated their activities individually, rather than collectively. As a result, little is known about their collective role in controlling bacteria populations and the cycling of nutrients. The goal of the proposed research is to address this gap in knowledge by investigating all three as a collective group under simulated natural conditions representing a range of temperature, salinity and abundance of prey. This project is conducted at two Historically Black Universities (HBCUs) with strong records of training and mentoring students and postdocs from underrepresented populations in science. The project benefits up to 100 students by providing unique and meaningful educational and research training experiences at the undergraduate and graduate student levels and for early-career scientist. Specific activities include courses on scientific writing and presenting results at annual project workshops as well as national and international scientific meetings. Graduate students are being trained in modern advanced methodologies in chemistry and microbiology. There is an ongoing assessment module to document education and training outcomes.
Up to now, the two mainly accepted mechanisms of mortality in bacterial populations are heterotrophic protist grazing and viral infection. Increasingly, it has become evident that an understudied group of predatory bacteria, BALOs, can also contribute to bacterial mortality. Yet, the mechanisms underlying the dynamics of BALO-prey interactions are poorly understood, as are the interactions among the micropredators, BALOs, protists and bacterial viruses. Ultimately, these processes may have contrasting influences on the structure and functioning of the microbial loop, including impacting higher trophic levels and biogeochemical cycles. The investigators hypothesize that environmental factors significantly influence how mortality in bacterial populations is partitioned among the micropredators. To test this hypothesis researchers are (1) investigating the interactions amongst the micropredators, (2) examining the molecular-level composition and dynamics of dissolved organic matter as the result of the different mortality processes by the NMR/ FT-ICR mass spectrometry (MS) hybrid approach, and (3) modeling these tri-trophic dynamics. Intellectual Merit: Results from this research will define a new mechanistic understanding of mortality dynamics that influence the microbial loop and oceanic biogeochemical cycles.
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.
