Biology Master Thesis Defense by Sharon Jacob
Advisor: Dr. Mark Silby
Committee: Dr. Christopher Brigham, Dr. Robert Drew
Abstract: Rhizobacteria such as Pseudomonas fluorescens Pf0-1 are important contributors to plant health due to their involvement in nutrient uptake, regulation of plant immunity, and inhibition of pathogens. P. fluorescens Pf0-1 mediates movement by using microscopic hair-like structures called flagella. Flagella synthesis is controlled by the bacterial enhancer binding protein (bEBP) FleQ; fleQ mutants are unable to swim. Taylor et al., (2015) showed that fleQ mutants eventually regain motility due to new mutations in ntrB and ntrC which result in elevated activation of NtrC and off-target binding of the bEBP NtrC to FleQ-controlled promoters. We hypothesized that if mutations that activate bEBPs can lead to crosstalk between regulatory networks, environmental signals that activate bEBPs may also influence crosstalk in a post-translational manner. We tested whether glutamate or alpha ketoglutarate which are predicted to activate AauR and MifR respectively could restore motility in the Pf0-1 fleQ mutant and found that the addition of glutamate restored motility. However, deletion of aauR did not abolish motility restoration, indicating that a different bEBP was important. Surprisingly, deletion of ntrC rendered glutamate unable to promote motility restoration, demonstrating that in the presence of glutamate wildtype NtrC can functionally replace FleQ in P. fluorescens. Measurement of transcription of the gene flhA which is normally FleQ-controlled confirmed that in the presence of glutamate, NtrC is capable of regulating expression of flagella genes. This research looks to provide an insight on how crosstalk between different regulatory pathways can increase the adaptability of bacteria in complex natural environments.
SENG-118
Mark Silby
5089998364
msilby@umassd.edu