Rhodococcus opacus high-cell-density batch cultivation with a bagasse hydrolysate for possible triacylglycerol synthesis

Abstract

Background: The promising use of lignocellulosic materials as a substrate for the synthesis of biochemical and biofuels has long been recognized. The bioconversion of all lignocellulosic sugars into useful products results in high sugar yields, which makes lignocelluloses appealing for use. Pretreatment and hydrolysis of lignocelluloses at high solids loadings are vital throughout industrial processes, making them more cost-effective and ecologically friendly by lowering the need for capital expenditures, energy use, and water use. The high expense of fermentation medium hinders heterotrophic oleaginous microorganisms' ability to metabolically synthesize single-cell oils for biodiesel use. This study's objective was to ascertain whether bagasse hydrolysate could be used as a cost-effective feedstock for oleaginous Rhodococcus opacus to produce microbial lipids. Methods: R. opacus a strain was used in this study. The culture was first of all maintained at soytone nutrient growth medium (i.e. GROTH MEDIUM 56) and subcultured at regular intervals and as well as preserved at 4°C. For the production media, a minimal salt medium is used. Sugarcane bagasse is pretreated by acidic hydrolysis followed by detoxification of hydrolysate and lipid extraction is done by Folch's extraction process. Results: After a brief adaptation/lag phase, the strain showed a viable growth pattern once the nutrients were detoxicated through the removal of inhibitors (e.g. hydroxymethyl-furfural [HMF]). R. opacus was grown via shake flask fermentation in bagasse hydrolysate with different sugar concentrations. When cultivated in S2 experiment, R. opacus obtained over 50% of its dry cell weight as a lipid with a lipid yield of 64.47% and productivity is 0.015 g/L/h. Conclusions: Depending on the available substrates, different microbial oils had different compositions. These findings suggest that lignocellulosic hydrolysate can be utilized as an inexpensive fermentation substrate for the R. opacus to produce microbial lipids. As a result, the range of uses for aqueous liquors produced by lignocellulosic pretreatment has increased, enabling further improvement.