Rhodococcus bacteria as a promising source of oils from olive mill wastes
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The accumulation of triacylglycerols (TAG) is a common feature among actinobacteria belonging to Rhodococcus genus. Some rhodococcal species are able to produce significant amounts of those lipids from different single substrates, such as glucose, gluconate or hexadecane. In this study we analyzed the ability of different species to produce lipids from olive oil mill wastes (OMW), and the possibility to enhance lipid production by genetic engineering. OMW base medium prepared from alperujo, which exhibited high values of chemical oxygen demand (127,000 mg/l) and C/N ratio (508), supported good growth and TAG production by some rhodococci. R. opacus, R. wratislaviensis and R. jostii were more efficient at producing cell biomass (2.2–2.7 g/l) and lipids (77–83% of CDW, 1.8–2.2 g/l) from OMW than R. fascians, R. erythropolis and R. equi (1.1–1.6 g/l of cell biomass and 7.1–14.0% of CDW, 0.1–0.2 g/l of lipids). Overexpression of a gene coding for a fatty acid importer in R. jostii RHA1 promoted an increase of 2.2 fold of cellular biomass value with a concomitant increase in lipids production during cultivation of cells in OMW. This study demonstrates that the bioconversion of OMW to microbial lipids is feasible using more robust rhodococal strains. The efficiency of this bioconversion can be significantly enhanced by engineering strategies.
KeywordsOlive mill wastes Bioconversion Lipid production Engineered Rhodococcus
The technical assistance of Enrique Rost for GC analyses and Pedro Torrecillas for chemical oxygen demand analyses is gratefully acknowledged.
This work was funded by Projects PIP2015-16 Nro 0529, PICT2012 Nro 2031, and Oil m&s SA company. Alvarez H.M and Lanfranconi M.P. are career researchers of the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina.
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Conflict of interest
The authors declare that they have no conflict of interest.
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