PNNL

Abstract

Lipids from microbes offer a promising source of renewable alternatives to petroleum-derived compounds. In particular, oleaginous microbes are of interest because they accumulate a large fraction of their biomass as lipids. In this study we analyzed genetic changes that alter lipid accumulation in Rhodobacter sphaeroides. By screening a R. sphaeroides Tn5-mutant library for insertions that increased fatty acid content, we identified ten high-lipid (HL) mutants for further characterization. These HL mutants exhibited increased sensitivity to drugs that target the bacterial cell envelope, changes in shape, and some had the ability to secrete lipids, with two HL mutants accumulating ~60% of their total lipids extracellularly. When one of the highest lipid secreting strains was grown in a fed-batch bioreactor its lipid content was comparable to that of oleaginous microbes, with the majority of the lipids secreted into the media. Based on the properties of these HL mutants, we conclude that alterations of the cell envelope are a previously unreported approach to increase microbial lipid production. We also propose that this approach may be combined with knowledge about biosynthetic pathways, in this or other microbes, to increase production of lipids and other chemicals.