Rhodococcus opacus B4: a promising bacterium for production of biofuels and biobased chemicals

Bacterial lipids have relevant applications in the production of renewable fuels and biobased oleochemicals. The genus Rhodococcus is one of the most relevant lipid producers due to its capability to accumulate those compounds, mainly triacylglycerols (TAG), when cultivated on different defined substrates, namely sugars, organic acids and hydrocarbons but also on complex carbon sources present in industrial wastes. In this work, the production of storage lipids by Rhodococcus opacus B4 using glucose, acetate and hexadecane is reported for the first time and its productivity compared with Rhodococcus opacus PD630, the best TAG producer bacterium reported. Both strains accumulated mainly TAG from all carbon sources, being influenced by the carbon source itself and by the duration of the accumulation period. R. opacus B4 produced 0.09 and 0.14 g L1 at 24 and 72 h, with hexadecane as carbon source, which was 2 and 3.3 fold higher than the volumetric production obtained by R. opacus PD630. Both strains presented similar fatty acids (FA) profiles in intact cells while in TAG produced fraction, R. opacus B4 revealed a higher variability in fatty acid composition than R. opacus PD630, when both strains were cultivated on hexadecane. The obtained results open new perspectives for the use of R. opacus B4 to produce TAG, in particular using oily (alkane-contaminated) waste and wastewater as cheap raw-materials. Combining TAG production with hydrocarbons degradation is a promising strategy to achieve environmental remediation while producing added value compounds.This work was financially supported by the Portuguese Science Foundation (FCT) and European Social Fund (ESF, POPH-QREN) through the Grant given to A.R. Castro (SFRH/BD/64500/2009), the FCT Strategic Project of UID/BIO/04469/2013 unit and COMPETE 2020 (POCI-01-0145-FEDER-006684) and project RECI/BBB-EBI/0179/2012 (FCOMP-01-0124-FEDER-027462)

The Effects of Model Aromatic Lignin Compounds On Growth and Lipid Accumulation of \u3ci\u3eRhodococcus rhodochrous\u3c/i\u3e

Lignocellulosic biomass is one of the most abundant and renewable organic materials in the world. The lignocellulosic complex is composed of cellulose, hemicellulose, and lignin, which can be pretreated to release sugars that can be utilized for microbial production of valued metabolites. Oleaginous microbes can accumulate over 20% of their cell dry weight as lipids, which are stored as intracellular energy reserves. The characterization of oleaginous bacteria creates opportunities for the development of alternative feedstocks and technologies. Rhodococcus rhodochrous is a bacterium recently determined to be oleaginous when grown in glucose-supplemented media. The purpose of this study was to evaluate model lignin phenolic compounds as substrates for lipid accumulation. Lipid accumulation in R. rhodochrous was evaluated using phenol, 4-hydroxybenzoic acid (HBA) and vanillic acid (VA) as model lignin compounds with and without glucose as a co-substrate. Cell dry weight increased in all treatments, indicating that growth was not impaired in these conditions. However, alterations were observed in the amount of lipids produced. Dry cell weight and lipids were analyzed daily. R. rhodochrous accumulated over 40% of its cell dry weight as lipids when grown in glucose with HBA and VA, but less than 20% when grown in HBA and VA alone. When grown in phenol and glucose, R. rhodochrous accumulated 35% of its dry weight at lipids, but did not accumulate lipids when grown in phenol alone. These data indicate that R. rhodochrous may have the capability to tolerate and utilize lignin-like aromatic compounds for lipid accumulation

Biology of triacylglycerol accumulation by Rhodococcus

Members of the genus Rhodococcus are specialist in the accumulation of triacylglycerols (TAG). Some of them can be considered oleaginous microorganisms since they are able to produce significant amounts of those lipids under certain conditions. In this context, R. opacus strain PD630 and R. jostii RHA1 became models among prokaryotes in this research area. The basic knowledge generated for rhodococci could be also extrapolated to related microorganisms with clinical importance, such as mycobacteria. The biosynthesis and accumulation of TAG by species of the genus Rhodococcus and other actinomycetes seems to be a process linked to the stationary growth phase or as a response to stress. The chemical structure of rhodococcal TAG can be controlled by the composition of the carbon source used. The biosynthesis and accumulation of novel TAG containing unusual components, such as aromatic and isoprenoid fatty acids, by members of Rhodococcus and related genera has been reported. The low specificity of wax ester synthase/diacylglycerol acyltransferase enzymes (WS/DGAT), which catalyze TAG biosynthesis in prokaryotes, may contribute to the high variability of TAG composition. The occurrence of genes coding for WS/DGAT enzymes is highly redundant in rhodococcal genomes. The enrichment of genes and enzymes involved in TAG metabolism in rhodococci suggest an important role of these lipids in the physiology of these microorganisms. Genomic, transcriptomic and proteomic data from TAG-accumulating rhodococci are now available and some genes coding for enzymes of the central metabolism, the Kennedy pathway, lipid transporter proteins, structural lipid inclusion bodies associated proteins, and transcriptional regulatory proteins have been identified and characterized. This article aims to summarize the most relevant achievements of basic research in this field, including the most recent knowledge emerged from studies on TAG accumulation by rhodococci.Fil: Alvarez, Hector Manuel. Universidad Nacional de la Patagonia "San Juan Bosco". Instituto de Biociencias de la Patagonia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto de Biociencias de la Patagonia; ArgentinaFil: Steinbüchel, Alexander. Westfälische Wilhelms Universität; Alemania. King Abdulaziz University; Arabia Saudit