Research Interests:
Microbial gene regulation; microbial community interactions; biofilms, biological control of soil-borne plant pathogens.

Current Research:
1. Secondary metabolite production in beneficial bacteria.
A. Molecular regulation of phenazine (PZ) production. We study the regulation and function of PZs in the root-associated bacterium Pseudomonas chlororaphis strain 30-84. PZs are nitrogen containing heterocyclic compounds originally classified as antibiotics. We showed that PZ production is regulated by a complex sensory network that includes quorum sensing, positive and negative two component regulation, and post-transcriptional regulation. Recent work has implicated additional regulatory systems in the fine-tuning of PZ production.
B. Multiples roles for secondary metabolites. The complex regulatory networks that control PZ production do not fit their role solely as competitive antibiotics. We hypothesize that PZ play multiple roles in the lifestyle of the producing bacterium and we are focused on identifying and understanding these additional functions for strain 30-84 in microbial physiology, microbe-microbe and plant-microbe interactions. Recently, we demonstrated that PZs are essential for biofilm development by strain 30-84 and that altering the ratio of endogenous PZs produced by strain 30-84 has profound effects on cell adhesion, biofilm architecture, and bacterial release. We are studying the roles of phenazine structural derivatives on cell adhesion, biofilm architecture, root colonization and plant nutrient uptake.

2. Signaling among microbial populations in vitro and in situ.
Phenazine production is regulated via quorum sensing which is dependent on diffusible microbial pheromones. Mutants defective in the production of these signals were rescued for phenazine production in vitro and in situ by signals produced by another subpopulation of the wheat rhizosphere community. Additionally, a second subpopulation was identified that inhibited phenazine production by the production of signals that interfere with normal quorum sensing activation of the phenazine biosynthetic operon. Thus, phenazine production is influenced directly by other members of the rhizosphere community. We are studying some of the negative signals produced by select rhizosphere strains both at the genetic level and their effects on strain 30-84 plant roots.

3. Microbial communities: involvement in speleothem formation. We are part of a Microbial Observatories project to analyze microbial communities and their contributions to speleothem formation in Kartchner Caverns, an oligotrophic carbonaceous cave in Arizona. We are characterizing communities via DGGE analysis and are developing the abilities to link metabolic capabilities to mineralization patterns, etc via metagenomics analysis. Our long term goal is to determine community stability and the influences of tourism on cave microbial communities.
Role of Graduate and Undergraduate Students in Research Projects: Both graduate and undergraduate students are essential contributors to our research. Projects performed by students include studies on promoter function and gene expression, identification of microbes that cross-communicate, identification of mechanisms of signal communication, biofilm development and iron acquisition. Students gain direct experience in all aspects of microbial genetics, from cloning, transposon mutagenesis, genetic complementation and DNA sequencing and analysis.