Production of a Polyunsaturated Isoprenoid Wax Ester during Aerobic Metabolism of Squalene by Marinobacter squalenivorans sp. nov

Abstract

This paper describes the production of 5,9,13-trimethyltetradeca-4E,8E,12-trienyl-5,9,13-trimethyltetradeca-4E,8E,12-trienoate during the aerobic degradation of squalene by a Marinobacter strain, 2Asq64, isolated from the marine environment. A pathway involving initial cleavage of the C 10 -C 11 or C 14 -C 15 double bonds of the squalene molecule is proposed to explain the formation of this polyunsaturated isoprenoid wax ester. The isoprenoid wax ester content reached 1.1% of the degraded squalene at the mid-exponential growth phase and then decreased during the stationary phase. The wax ester content increased by approximately threefold in N-limited cultures, in which the ammonium concentration corresponds to conditions often found in marine sediments. This suggests that the bacterial formation of isoprenoid wax esters might be favored in such environments. The bacterial strain is then characterized as a member of a new species, for which we propose the name Marinobacter squalenivorans sp. nov.The microbial communities of marine environments are often exposed to fluctuating conditions such as the availability of nutrients. Microorganisms have developed a variety of strategies that allow them to survive in these variable environments; the accumulation of storage lipids is only one of them (4). Storage compounds occur normally as intracellular inclusions in bacteria (42). While the accumulation of triacylglycerols occurs preferentially in eukaryotic organisms, triacylglycerols are not frequently found as storage compounds in bacteria (4). Bacteria usually accumulate specialized lipids such as poly(3-hydroxybutyric acid) or other polyhydroxyalkanoic acids (31,44,45). Only some bacteria of the genera Mycobacterium (6), Streptomyces (29), and Rhodococcus (3, 5, 50) accumulate triacylglycerols. Wax esters, which are trace constituents of numerous bacteria (e.g., Escherichia coli [28], Serratia marcescens, Bacillus cereus [22], Nocardia sp. [21], and Thiobacillus thioparus [15]), are generally considered as widespread energy storage components in the genus Acinetobacter (18). In fact, it was previously demonstrated that different strains of A. calcoaceticus increased their wax ester contents in N-limited cultures and that the accumulated wax esters were degraded to water-soluble molecules and CO 2 during C starvation (18). These results showed that these compounds may serve as an ATP-generating substrate during starvation.We previously observed the production of several isoprenoid wax esters during the aerobic degradation of 6,10,14-trimethylpentadecan-2-one and phytol by four bacteria (Acinetobacter sp. strain PHY9, Pseudomonas nautica [IP85/617], Marinobacter sp. strain CAB [DSMZ11874], and Marinobacter hydrocarbonoclasticus [ATCC49840]) isolated from the marine environment (33). The amount of these esters increased considerably in N-limited cultures, in which the ammonium concentration corresponds to conditions often found in marine sediments. Similar isoprenoid wax esters have also been detected during the degrada...

Biosynthesis of Isoprenoid Wax Ester inMarinobacter hydrocarbonoclasticusDSM 8798: Identification and Characterization of Isoprenoid Coenzyme A Synthetase and Wax Ester Synthases

“…The differences in substrate selectivities and activities seen in the isoprenoid WSs described here, reported from Acinetobacter baylyi ADP1 (11,23,25), and more recently reported from Alcanivorax borkumensis (12) may reflect adaptations to available carbon sources in their respective environments (15)(16)(17). Identification of additional microbial WE biosynthetic genes will likely yield enzymes with new and interesting substrate selectivities.…”

“…Microbial WEs have been found in Mycobacterium (4), Rhodococcus (1), Acinetobacter (2), and Marinobacter (15,17) strains that grow in environments where a carbon source (such as petroleum hydrocarbons [9] and gluconate [11]) may be abundant relative to other nutrients such as phosphorous and nitrogen. Acyl WEs are synthesized from long-chain fatty alcohol and fatty acyl-coenzyme A (CoA) substrates.…”

“…The gamma proteobacteria Marinobacter hydrocarbonoclasticus DSM 8798 (referred to here as strain 8798) has been shown to synthesize an isoprenoid WE when grown on phytol as the sole carbon source and under nitrogen-limiting conditions (15,17). It has been proposed that exogenous phytol is transported into the cell, where it is converted into an inter-mediate aldehyde (phytenal) that is then further oxidized into the isoprenic fatty acid phytenic acid, which may be hydrogenated into phytanic acid (17).…”

“…Another class of WEs is the isoprenoid WEs that are made from branched, long-chained isoprenoyl alcohol and isoprene fatty acid substrates. Isoprenoid WEs have been identified as a way to provide energy storage in Marinobacter species (15)(16)(17). Marinobacter species grow in marine sediment materials where there is an abundance of recalcitrant acyclic isoprenoid alcohols such as farnesol and phytol, which are derived from (bacterio)chlorophyll molecules (16,17).…”

Acyltransferases in Bacteria

“…The Gram-negative, marine bacterium M. hydrocarbonoclasticus is able to utilize various hydrocarbons and isoprenoids as sole carbon and energy sources (84). Furthermore, like some other marine bacteria, M. hydrocarbonoclasticus can accumulate (polyunsaturated) isoprenoid WE upon degradation of phytol, farnesol squalene, or similar chlorophyll-derived compounds, which are abundant in the marine sediment (32,(85)(86)(87).…”