Petroleum (or crude oil) is a complex mixture of hydrocarbons. Annually, millions of tons of crude petroleum oil enter the marine environment from either natural or anthropogenic sources. Hydrocarbon-degrading bacteria (HDB) are able to assimilate and metabolize hydrocarbons present in petroleum. Crude oil pollution constitutes a temporary condition of carbon excess coupled to a limited availability of nitrogen that prompts marine oil-degrading bacteria to accumulate storage compounds. Storage lipid compounds such as polyhydroxyalkanoates (PHAs), triacylglycerols (TAGs), or wax esters (WEs) constitute the main accumulated lipophilic substances by bacteria under such unbalanced growth conditions. The importance of these compounds as end-products or precursors to produce interesting biotechnologically relevant chemicals has already been recognized. In this review, we analyze the occurrence and accumulation of lipid storage in marine hydrocarbonoclastic bacteria. We further discuss briefly the production and export of lipophilic compounds by bacteria belonging to the Alcanivorax genus, which became a model strain of an unusual group of obligate hydrocarbonoclastic bacteria (OHCB) and discuss the possibility to produce neutral lipids using A. borkumensis SK2.
Triacylglycerols (TAGs), wax esters (WEs), and polyhydroxyalkanoates (PHAs) are the major hydrophobic compounds synthesized in bacteria and deposited as cytoplasmic inclusion bodies when cells are cultivated under imbalanced growth conditions. The intracellular occurrence of these compounds causes high costs for downstream processing. Alcanivorax species are able to produce extracellular lipids when the cells are cultivated on hexadecane or pyruvate as the sole carbon source. In this study, we developed a screening procedure to isolate lipid export-negative transposon-induced mutants of bacteria of the genus Alcanivorax for identification of genes required for lipid export by employing the dyes Nile red and Solvent Blue 38. Three transposoninduced mutants of A. jadensis and seven of A. borkumensis impaired in lipid secretion were isolated. All isolated mutants were still capable of synthesizing and accumulating these lipids intracellularly and exhibited no growth defect. In the A. jadensis mutants, the transposon insertions were mapped in genes annotated as encoding a putative DNA repair system specific for alkylated DNA (Aj17), a magnesium transporter (Aj7), and a transposase (Aj5). In the A. borkumensis mutants, the insertions were mapped in genes encoding different proteins involved in various transport processes, like genes encoding ( Almost all prokaryotes synthesize lipophilic storage substances as an integral part of their metabolism under limited nitrogen or phosphorus conditions if there is an excess of a suitable carbon source at the same time. The accumulated storage lipids serve as energy and carbon sources during starvation periods, and they are mobilized again under conditions of carbon and energy deficiency. The majority of the members of many genera synthesize hydrophobic polymers, such as poly(3-hydroxybutyrate) (PHB) or other types of polyhydroxyalkanoates (PHAs), whereas the accumulation of triacylglycerols (TAGs; trioxoesters of glycerol and long-chain fatty acids [FAs]) or wax esters (WEs; oxoesters of primary long-chain fatty acids and primary long-chain fatty alcohols) occurs in fewer prokaryotes (66). TAG accumulation has been reported for species of the genera Streptomyces, Mycobacterium, Nocardia, Rhodococcus (4,6,65), and recently also Alcanivorax and other hydrocarbonoclastic marine bacteria (32). Accumulation of WEs has been frequently reported for species of the genus Acinetobacter (66) but also for marine bacteria, such as Marinobacter (50) and Alcanivorax (11,32).In general, the accumulation of at least one type of these compounds occurs intracellularly under imbalanced growth conditions in almost all prokaryotes. The localization of neutral lipids in marine organisms is not restricted to the cell cytoplasm, as extracellular lipid deposition has been shown in studies with Alcaligenes sp. PHY9 and Pseudomonas nautica (24). The production of extracellular wax esters by Alcanivorax jadensis T9 growing on hexadecane was described a few years ago (11). Species of the genus Alcanivorax ...
Triacylglycerols (TAG) and wax esters (WE) constitute together with polyhydroxyalkanoates (PHA) the major storage lipophilic compounds in prokaryotes. Recently, the production of neutral lipids such as TAG and WE has been reported in species of the genus Alcanivorax, which belongs to the group of obligate hydrocarbonoclastic bacteria (OHCB). We analyzed the production of such neutral lipids by different marine hydrocarbonoclastic bacteria growing on pyruvate or hexadecane as sole carbon source, and compared it to other bacteria such as Rhodococcus opacus strain PD630 and Acinetobacter baylyi strain ADP1, which are two well-studied strains for production of neutral lipids. Alcanivorax borkumensis SK2 synthesized mainly TAG when cells are cultivated on pyruvate, while biosynthesis and accumulation of WE was mainly observed in cells growing on hexadecane. Alcanivorax jadensis T9 synthesized and accumulated mainly WE if cells were cultivated with hexadecane, while both TAG and WE were observed if cells were cultivated with pyruvate as sole carbon source, respectively. Predominantly production as well as export of WE was observed in Marinobacter hydrocarbonoclasticus SP17 growing on pyruvate or hexadecane as sole carbon source. The chemical structures of TAG and WE produced by A. borkumensis SK2 were analyzed by gas chromatography and/or mass spectrometry, and first studies to investigate the influence of different C/N ratio (7, 50 or 150) on the production of neutral lipids were performed.
In many microorganisms, the key enzyme responsible for catalyzing the last step in triacylglycerol (TAG) and wax ester (WE) biosynthesis is an unspecific acyltransferase which is also referred to as wax ester synthase/acyl coenzyme A (
The objective of this work was to determine (1) the effect of rotational speed (N) and lifters on the oxygen transfer coefficient (k (L)) of a mineral solution and (2) the effect of solids concentration of a slurry soil-mineral solution on k (L), at a fixed value N (0.25 s(-1)); in both cases the treatment was carried out in an aerated rotating drum reactor (RDR) operated at atmospheric pressure. First, the k (L) for the mineral solution was in the range 6.38 x 10(-4)-7.69 x 10(-4) m s(-1), which was of the same order of magnitude as those calculated for closed rotating drums supplied with air flow. In general, k (L) of RDR implemented with lifters was superior or equal to that of RDR without lifters. For RDR implemented with lifters, k (L) increased with N in the range 6.65 x 10(-4)-10.51 x 10(-4) m s(-1), whereas k (L) of RDR without lifters first increased with N up to N = 0.102 s(-1), and decreased beyond this point. Second, regarding soil slurry experiments, an abrupt fall of k (L) (ca. 50%) at low values of the solid concentration (C (v)) and an asymptotic pattern at high C (v) were observed at N = 0.25 s(-1). These results suggest that mass transfer phenomena were commanded by the slurry properties and a semi-empirical equation of the form Sh = f(Re, Sc) seems to corroborate this finding.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.