oa Controls on 3-Methylhopanoid Production by the Bacterium Methylococcus Capsulatlus During Continuous Culture Growth

3-Methylhopanoids are a subset of bacterially derived lipids that are predominantly synthesized by methanotrophic proteobacteria and historically have been used as an indicator of aerobic bacterial methanotrophy. The recalcitrant nature of hopanoid hydrocarbons allows for the preservation of 3-methylhopanoid compounds in ancient sediments, and this has provided key insights into the evolution and distribution of aerobic methane oxidizing metabolisms throughout the geologic record. However, several concerns remain that confound the use of these lipid biomarker tools for reconstructing methanotrophy in modern and ancient marine environments: (1) the environmental factors controlling 3-methylhopanoid production have not been determined, (2) it is unclear what physiological role(s) these compounds play in the cell, and (3) controls on the isotopic variability of 3-methylhopanoids in extant bacteria or the rock record are unknown. In this study we address these unknowns by performing chemostat growth experiments under a range of constant temperature, CH4, O2, and nutrient levels using Methylococcus capsulatus, a well-studied obligate methanotroph and known 3-methylhopanoid producer, and a knock out mutant (lacking 3-methylhopanoid biosynthesis genes).