Microbiology

Jorgenson successfully defends PhD thesis

Jorgenson defense

Matthew Jorgenson, a student in the Interdisciplinary Graduate Program in Genetics, successfully defended his PhD thesis, "Breaking down walls: studies of RlpA from Pseudomonas aeruginosa," on Monday, July 7, 2014. Matt is pictured here with his mentor, David Weiss, PhD.

Rare lipoprotein A (RlpA) has been studied previously only in Escherichia coli, where it localizes to the septal ring and scattered foci along the lateral wall, but mutants have no phenotypic change. In this thesis, we show rlpA mutants of Pseudomonas aeruginosa form chains of short, fat cells when grown in media of low osmotic strength. These morphological defects indicate RlpA is needed for efficient separation of daughter cells and maintenance of rod shape. Analysis of peptidoglycan sacculi from a ΔrlpA mutant revealed increased tetra and hexasaccharides that lack stem peptides (hereafter called “naked glycans”). Incubation of these sacculi with purified RlpA resulted in release of naked glycans containing 1,6-anhydro N-acetylmuramic acid ends. RlpA did not degrade sacculi from wild-type cells unless the sacculi were subjected to a limited digestion with an amidase to remove some of the stem peptides. Collectively, these findings indicate RlpA is a lytic transglycosylase with a strong preference for naked glycan strands. We propose that RlpA activity is regulated in vivo by substrate availability, and that amidases and RlpA work in tandem to degrade peptidoglycan in the division septum and lateral wall.

Our discovery that RlpA from P. aeruginosa is a lytic transglycosylase motivated us to reinvestigate RlpA from E. coli. We confirmed predictions that RlpA of E. coli is an outer membrane protein and determined its abundance to be about 600 molecules per cell. However, multiple efforts to demonstrate that E. coli RlpA is a lytic transglycosylase were unsuccessful and the function of this protein in E. coli remains obscure.

ABOUT MATT

Matt grew up in Kasson, MN—home of the first stoplight in the whole county. His interest in science was fostered by his parents and grew through competition in various categories in the Science Olympiad program (state champ in Rube Goldberg!). After graduating high school, he attended Northwestern College in St. Paul, MN, where he majored in Biology. Matt’s first research experience was working on intron splicing in Lactococcus lactis with Dr. Joanna Klein, an alumna of the University of Iowa Interdisciplinary Graduate Program in Genetics. This project sparked Matt’s interest in microbiology and on the advice of his mentor, he decided to pursue a PhD. Dr. Klein suggested her alma mater as a potential landing spot, which turned out to be a perfect fit.

Matt entered the Genetics Program in the fall of 2009 and joined David Weiss’ lab in the Department of Microbiology in the spring of 2010. Since then, Matt has studied various aspects of cell division in Escherichia coli and Pseudomonas aeruginosa. He has presented his research at Virginia Tech in Blacksburg, VA, the Molecular Genetics of Bacteria and Phages meeting in Madison, WI, and the West Coast Bacterial Physiologists meeting in Pacific Grove, CA. His discovery of a new enzyme involved in cell wall degradation in P. aeruginosa was recently published in Molecular Microbiology, and two additional papers are in progress.

Matt loves teaching and has enjoyed mentoring three undergraduate students (and Eric) during his time in graduate school.

Following successful completion of his PhD, Matt and his family will be moving to Little Rock, AR, where he has accepted a postdoctoral position in the lab of Kevin Young at the University of Arkansas for Medical Sciences. Dr. Young’s lab studies cell wall metabolism and cell shape in E. coli.

When Matt is away from lab, he enjoys spending time with his family—wife, Michelle; daughters, Claudia and Eleanor—and church, binge watching sci-fi shows, running, playing softball, and talking all things Minnesota sports.