Widespread Head-to-Head Hydrocarbon Biosynthesis in Bacteria and Role of OleA

Abstract

Previous studies identified the oleABCD genes involved in head-to-head olefinic hydrocarbon biosynthesis. The present study more fully defined the OleABCD protein families within the thiolase, ␣/␤-hydrolase, AMPdependent ligase/synthase, and short-chain dehydrogenase superfamilies, respectively. Only 0.1 to 1% of each superfamily represents likely Ole proteins. Sequence analysis based on structural alignments and gene context was used to identify highly likely ole genes. Selected microorganisms from the phyla Verucomicrobia, Planctomyces, Chloroflexi, Proteobacteria, and Actinobacteria were tested experimentally and shown to produce longchain olefinic hydrocarbons. However, different species from the same genera sometimes lack the ole genes and fail to produce olefinic hydrocarbons. Overall, only 1.9% of 3,558 genomes analyzed showed clear evidence for containing ole genes. The type of olefins produced by different bacteria differed greatly with respect to the number of carbon-carbon double bonds. The greatest number of organisms surveyed biosynthesized a single long-chain olefin, 3,6,9,12,15,19,22,25,28-hentriacontanonaene, that contains nine double bonds. Xanthomonas campestris produced the greatest number of distinct olefin products, 15 compounds ranging in length from C 28 to C 31 and containing one to three double bonds. The type of long-chain product formed was shown to be dependent on the oleA gene in experiments with Shewanella oneidensis MR-1 ole gene deletion mutants containing native or heterologous oleA genes expressed in trans. A strain deleted in oleABCD and containing oleA in trans produced only ketones. Based on these observations, it was proposed that OleA catalyzes a nondecarboxylative thiolytic condensation of fatty acyl chains to generate a ␤-ketoacyl intermediate that can decarboxylate spontaneously to generate ketones.

Effects of Aerobic Growth on the Fatty Acid and Hydrocarbon Compositions of <i>Geobacter bemidjiensis</i> Bem^T

“…3a and 3b . The detection of C31:9 in G. bemidjiensis Bem T is consistent with the study reported by Sukovich et al 18 , and strongly indicates the presence of LC-PUFAs in this bacterium because the synthesis of one mole of C31:9 requires two moles of 4Z,7Z,10Z,13Z -hexadec-4,7,10,13-tetraenoic acid 16:4 as a substrate, which is a product and a precursor of EPA and DHA of PUFA synthase 23 . However, no clear peaks corresponding to EPA or DHA were detected Fig.…”

“…Although G. bemidjiensis Bem T produces C31:9 18 , its ability to synthesize LC-PUFAs is unknown. Bacterial LCPUFAs possess multiple bis-allylic hydrogens, which act unexpectedly as antioxidants, and are highly susceptible to oxidation 4,5,7,19,20 .…”

“…Among the four peaks, only U 3 was detected in type 2 and type 3 cultures data not shown . One possible explanation for why G. bemidjiensis Bem T does not produce LC-PUFAs would be that as soon as PUFAs are synthesized by the Pfa enzyme complex, they may be utilized as substrates for Ole proteins, which produce C31:9 through the head-to-head fatty acid condensation mechanism 18 .…”

Active Multienzyme Assemblies for Long-Chain Olefinic Hydrocarbon Biosynthesis

“…The cellular function(s) of the ole gene cluster has been studied only in Shewanella oneidensis MR-1. The presence of the oleABCD genes was found to promote more rapid cell growth during a shift to colder temperatures, consistent with those genes being commonly found in cold-temperature bacteria from polar and marine environments (4)(5)(6). However, bacteria containing ole gene clusters inhabit a diversity of ecological niches, suggesting there may be a range of functions for long-chain olefinic hydrocarbons.…”

“…A subsequent study in 2010 reported the presence of the four hydrocarbon biosynthetic genes, oleABCD, in 69 prokaryotes from many deeply rooted branches of the prokaryotic tree of life ( Fig. 1) (4). The cellular function(s) of the ole gene cluster has been studied only in Shewanella oneidensis MR-1.…”