Novel signaling mechanisms regulating biofilm formation in Bacillus subtilis

Abstract

Associate Professor of Biology would not be where I am today without all of you. To the LONG squad (past and present) -thank you for letting a scientist be a history nerd and play lawn games all these years. It means the world to me. To the many friends I made along the way-thank you for the love and support you have given me over the years. Dan-thanks for starting so many conversations we'll never finish, giving me an excuse to leave the lab, and of course, introducing me to my favorite brothers that I am not related to. I never would have gotten through grad school without them. To John and Hank Green, for never forgetting to be awesome and giving me an escape from grad school. To Hank, thank you for helping me identify what my passions are and being an inspirational science communicator.Finally, and most importantly, thank you to my family. Your unconditional love and support has brought me to where I am and I could not have done it without you. This degree belongs as much to you as it does to me, if not more so. Mom-you never let me give up, and I don't tell you often enough how much I appreciate that. Aunt Marge-thank you for everything you've done to support me all of these years. Joe-thanks for keeping me humble and reminding me to be normal. Sorry I'll never remember. Abstract of DissertationBacteria are capable of forming multicellular communities, known as biofilms. Bacillus subtilis is a Gram-positive, rod shaped, soil-dwelling bacterium often used as a model organism to study biofilm formation. Both extracellular and intracellular signals can trigger biofilm formation through a signaling cascade, which turns on genes involved in production of the biofilm matrix. In B. subtilis, the matrix consists of an exopolysaccharide (EPS) component and two protein components, which are regulated on a genetic level by two master regulators, SinR and AbrB.Biosynthesis of the EPS is also regulated at the post-translational level, by a bacterial tyrosine kinase (BY-kinase), EpsB, which is encoded within the same operon as the enzymes involved in the biosynthesis of EPS. EpsB is activated by EpsA, which senses EPS in a quorum-sensing-like manner. We show genetic evidence for EpsB activation by TkmA, a modulator of a different BYkinase can activate EpsB. This cross-talk allows B. subtilis to increase the signals to which it can respond.Intracellularly, serine starvation triggers biofilm formation. We elucidate the mechanism by which this occurs and investigate the regulation of serine biosynthesis. Expression of serA, which encodes SerA, the enzyme responsible for the first and rate-limiting step of serine biosynthesis decreases upon entry into stationary phase and is regulated by catabolite control. This regulation allows cells to trigger biofilm formation based on available nutrients as well as external stimuli.Accompanying this decrease in serine is a decrease in seryl-tRNA isoacceptors, responsible for adding serine to growing peptide chains in the ribosome. It was previously observed that ribosomes pause on specif...