Leland (Sandy) Pierson III

Professional Summary

Research Emphasis:

1. Secondary metabolite production in beneficial bacteria.

Molecular regulation and roles of phenazines (PZ). We study the regulation and function of PZs in the root-associated bacterium Pseudomonas chlororaphis strain 30-84 and the opportunistic pathogen P. aeruginosa. PZs are nitrogen containing heterocyclic compounds produced by a wide range of soil and root-associated bacteria that are required for biofilm formation and persistence in the rhizosphere. These compounds additionally inhibit the growth of several pathogenic fungi. PZ production is regulated by a complex sensory network that includes quorum sensing, positive and negative two component regulation, and post-transcriptional regulation. Ongoing work includes the generation of bacterial derivatives producing structural PZ variants and transcriptomic analyses of the mechanisms involved in PZ regulation and in elucidating the multiple roles PZs play for the producing bacterium.

2. Signaling among microbial populations in vitro and in situ.

Phenazine (PZ) production is regulated via quorum sensing which is dependent on the accumulation of diffusible microbial pheromones. Mutants defective in the production of these signals were rescued for PZ production in vitro and in situ by signals produced by another subpopulation of the wheat rhizosphere community. Additionally, we identified a second subpopulation from the wheat rhizosphere that inhibited PZ production via the production of non-AHL signals that interfered with normal quorum sensing activation of the PZ biosynthetic operon. Thus, PZ 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 are examining their effects on PZ expression by strain 30-84 on plant roots.