Overall research goals
Nutrient cycling in natural environments is mostly a consequence of microbial behavior. However, these organisms act on entirely different temporal and spatial scales than the plants and animals that appear to dominate terrestrial systems. I believe that understanding the motivations for, and consequences of, microbial metabolism is key to understanding how nutrients such as nitrogen, phosphorus and carbon move through natural systems. I particularly like asking questions about microbes with exotic metabolic capabilities beyond those of plants and animals (for example, chemoautotrophy, nitrogen fixation, anaerobic respiration, etc.). Though my work thus far has mostly focused on the microbes involved in the terrestrial nitrogen cycle, I hope to expand my work to new elements and new environments in the future.
Below I've given synopses of projects I find particularly interesting; this list is by no means exhaustive but I hope it will give you a taste of my current and past research interests.
Ecosystem-level regulation of nitrogen fixation by free-living diazotrophs
Free-living diazotrophs have access to a variety of N sources in soils and likely do not rely entirely on fixation to meet their cellular N demand. Though labile N has been shown to inhibit fixation in pure culture, few studies have focused on the role that recalcitrant N plays in regulating this important process. I have found that many of these organisms have the ability to access recalcitrant N pools through exoenzyme excretion, which leads to an interesting question: when diazotrophs run out of labile N, do they fix N or release exoenzymes to acquire recalcitrant N? Understanding the decision-making strategies employed by these organisms in soils (which contain large amounts of recalcitrant N) is key to unraveling process-level regulation of N fixation by free-living diazotrophs.
My postdoctoral advisor Maren Friesen and I have a paper in review that outlines a new conceptual framework for understanding the role that N fixation plays in the cellular N budget of free-living diazotrophs, which was developed from a careful reading of pure-culture literature, but has ecosystem-level implications for soil N cycling. We also developed these ideas into a pre-proposal, which we submitted to NSF-DEB in 2015. Surprisingly, our program officer invited us to submit an EAGER grant based on these ideas, which was later funded! Thanks to NSF for giving us an opportunity to investigate key predictions of the LAR N-acquisition strategy at the organismal and ecosystem scale! I see our EAGER grant as the beginning of a long series of investigations in years to come!
Nutrient cycling in natural environments is mostly a consequence of microbial behavior. However, these organisms act on entirely different temporal and spatial scales than the plants and animals that appear to dominate terrestrial systems. I believe that understanding the motivations for, and consequences of, microbial metabolism is key to understanding how nutrients such as nitrogen, phosphorus and carbon move through natural systems. I particularly like asking questions about microbes with exotic metabolic capabilities beyond those of plants and animals (for example, chemoautotrophy, nitrogen fixation, anaerobic respiration, etc.). Though my work thus far has mostly focused on the microbes involved in the terrestrial nitrogen cycle, I hope to expand my work to new elements and new environments in the future.
Below I've given synopses of projects I find particularly interesting; this list is by no means exhaustive but I hope it will give you a taste of my current and past research interests.
Ecosystem-level regulation of nitrogen fixation by free-living diazotrophs
Free-living diazotrophs have access to a variety of N sources in soils and likely do not rely entirely on fixation to meet their cellular N demand. Though labile N has been shown to inhibit fixation in pure culture, few studies have focused on the role that recalcitrant N plays in regulating this important process. I have found that many of these organisms have the ability to access recalcitrant N pools through exoenzyme excretion, which leads to an interesting question: when diazotrophs run out of labile N, do they fix N or release exoenzymes to acquire recalcitrant N? Understanding the decision-making strategies employed by these organisms in soils (which contain large amounts of recalcitrant N) is key to unraveling process-level regulation of N fixation by free-living diazotrophs.
My postdoctoral advisor Maren Friesen and I have a paper in review that outlines a new conceptual framework for understanding the role that N fixation plays in the cellular N budget of free-living diazotrophs, which was developed from a careful reading of pure-culture literature, but has ecosystem-level implications for soil N cycling. We also developed these ideas into a pre-proposal, which we submitted to NSF-DEB in 2015. Surprisingly, our program officer invited us to submit an EAGER grant based on these ideas, which was later funded! Thanks to NSF for giving us an opportunity to investigate key predictions of the LAR N-acquisition strategy at the organismal and ecosystem scale! I see our EAGER grant as the beginning of a long series of investigations in years to come!
Superoxide-dependent nitrogen fixation by Streptomyces thermoautotrophicus
This project (which funded my initial postdoc appointment at MSU) was designed to investigate a novel pathway for nitrogen fixation known as super-oxide dependent nitrogen fixation (SDN fixation), which could have implications for biotechnology. Specifically, my postdoc advisor Maren Friesen secured grant money to investigate the feasibility of transferring SDN fixation to non-leguminous crops through an Ideas Lab grant jointly-funded by NSF and BBSRC. However, step 1 for this project was to re-isolate S. thermoautotrophicus, the organism in which SDN fixation was first reported, as it was no longer available in public culture collections. During the course of this project, I was driven to understand the environmental implications of SDN fixation, an unusual form of N-fixation said to be powered by carbon monoxide and dependent on the presence of oxygen!
To hunt for S. thermoautotrophicus, my post doc advisor Maren Friesen and I went to Centralia PA, a town abandoned due to an underground mine fire, which has been burning for over 50 years! A multi-institutional publication on our findings is upcoming so I'll leave it there for now....
This project (which funded my initial postdoc appointment at MSU) was designed to investigate a novel pathway for nitrogen fixation known as super-oxide dependent nitrogen fixation (SDN fixation), which could have implications for biotechnology. Specifically, my postdoc advisor Maren Friesen secured grant money to investigate the feasibility of transferring SDN fixation to non-leguminous crops through an Ideas Lab grant jointly-funded by NSF and BBSRC. However, step 1 for this project was to re-isolate S. thermoautotrophicus, the organism in which SDN fixation was first reported, as it was no longer available in public culture collections. During the course of this project, I was driven to understand the environmental implications of SDN fixation, an unusual form of N-fixation said to be powered by carbon monoxide and dependent on the presence of oxygen!
To hunt for S. thermoautotrophicus, my post doc advisor Maren Friesen and I went to Centralia PA, a town abandoned due to an underground mine fire, which has been burning for over 50 years! A multi-institutional publication on our findings is upcoming so I'll leave it there for now....
The relative roles of ammonia-oxidizing bacteria and archaea in temperate forest soils
Though there is only one arrow for ammonia oxidation (the rate-limiting step of nitrification) on the nitrogen cycle, this important process results from the combined actions of two different groups of microbes: ammonia oxidizing bacteria (AOB) and archaea (AOA). The relative abundance and activity of these two groups has ecosystem-level consequences since AOA and AOB have different ammonia uptake kinetics and oxidation rates. I sought to disentangle the roles of AOA and AOB in temperate forest soils by monitoring their growth alongside ammonia-oxidation during in situ incubations. My collaborators and I used a multiple-regression analysis to show that both groups have a role in ammonia oxidation across several temperate forest sites, and we were even able to convert growth in gene copy numbers to units of carbon to calculate a growth efficiency for each group in the field (turns out they are remarkably close)!
This work, a large part of my Dissertation in the Barrett lab at Virginia Tech, was entirely conducted at Coweeta LTER. Coweeta is an NSF-sponsored site designed to study the long term implications of land management on water quality; its also one of the most gorgeous places on the planet. Though we've already published a couple of papers in this area, my collaborator Laurence Lin, a postdoc at UNC who specializes in ecosystem modeling, continues to help me explore these data in new and interesting ways. Look for interesting modeling papers on this work in years to come!
Though there is only one arrow for ammonia oxidation (the rate-limiting step of nitrification) on the nitrogen cycle, this important process results from the combined actions of two different groups of microbes: ammonia oxidizing bacteria (AOB) and archaea (AOA). The relative abundance and activity of these two groups has ecosystem-level consequences since AOA and AOB have different ammonia uptake kinetics and oxidation rates. I sought to disentangle the roles of AOA and AOB in temperate forest soils by monitoring their growth alongside ammonia-oxidation during in situ incubations. My collaborators and I used a multiple-regression analysis to show that both groups have a role in ammonia oxidation across several temperate forest sites, and we were even able to convert growth in gene copy numbers to units of carbon to calculate a growth efficiency for each group in the field (turns out they are remarkably close)!
This work, a large part of my Dissertation in the Barrett lab at Virginia Tech, was entirely conducted at Coweeta LTER. Coweeta is an NSF-sponsored site designed to study the long term implications of land management on water quality; its also one of the most gorgeous places on the planet. Though we've already published a couple of papers in this area, my collaborator Laurence Lin, a postdoc at UNC who specializes in ecosystem modeling, continues to help me explore these data in new and interesting ways. Look for interesting modeling papers on this work in years to come!