PNNL

Abstract

Understanding the mechanisms of lipid accumulation in microorganisms is 30 important for several reasons. In addition to providing insight into assembly of 31 biological membranes, lipid accumulation has important applications in the 32 production of renewable fuels and chemicals. The photosynthetic bacterium 33 Rhodobacter sphaeroides is an attractive organism to study lipid accumulation, as it 34 has the somewhat unique ability to increase membrane production at low O2 35 tensions. Under these conditions, R. sphaeroides develops invaginations of the 36 cytoplasmic membrane to increase its membrane surface area for housing of the 37 membrane----bound components of its photosynthetic apparatus. Here we use fatty 38 acid levels as a reporter of membrane lipid content. We show that, under low O2 and 39 anaerobic conditions, the total fatty acid content per cell increases 3----fold. We also 40 find that the increases in the amount of fatty acid and photosynthetic pigment per 41 cell are correlated as O2 tensions or light intensity are changed. To ask if lipid and 42 pigment accumulation were genetically separable, we analyzed strains with 43 mutations in known photosynthetic regulatory pathways. While a strain lacking 44 AppA failed to induce photosynthetic pigment----protein complex accumulation, it 45 increased fatty acid content under low O2 conditions. We also found that an intact 46 PrrBA pathway is required for low O2----induced fatty acid accumulation. Our findings 47 suggest a previously unknown role of R. sphaeroides transcriptional regulators in 48 increasing fatty acid and phospholipid accumulation in response to decreased O2 49 tension.