An Investigation for Novel Cell Length Determinants in Caulobacter crescentus Reveals Unexpected Link to Metabolic Processes

Abstract

Bacteria come in a diversity of cell shapes that facilitate their ability to thrive in a variety of environments. Specifically, the length of a given bacterium is important for maintaining a favorable surface area to volume ratio, which aids the bacterium in nutrient intake. Additionally, factors which regulate length serve as antibiotic targets because they are unique to bacteria. An excellent model organism to study cell shape is Caulobacter crescentus, an aquatic, rod-shaped bacterium. Caulobacter’s shape determinants have been the subject of research for many years. However, no study thus far has comprehensively surveyed all possible Caulobacter mutants for defects in length. In this thesis research, I performed a qualitative microscopy screen in a subset of an ordered transposon library being actively constructed to assemble a list of Caulobacter genes related to length. From the screen, I identified over fifty candidates with visible shape defects and confirmed them both phenotypically and genetically. I then attempted to characterize a cobalamin biosynthesis protein gene, confirming its role in the vitamin B12 biosynthesis pathway. Through this experiment, I also unexpectedly shed light on a lesser-known cell growth paradigm, which unites cell growth, shape, and metabolism in active growth regulation during prolonged stationary phase. Many of the identified factors are uncharacterized and conserved among other Gram-negative bacteria. Their conservation indicates they may play a fundamental role in cell elongation, division, and life cycle regulation. These novel factors also provide an opportunity to elucidate the full mechanism of shape determination and grant insight into new antibiotic targets.