Microbial lipid production by oleaginous Rhodococci cultured in lignocellulosic autohydrolysates

Abstract

Metabolic synthesis of single cell oils (SCOs) for biodiesel application by heterotrophic oleaginous microorganisms is being hampered by the high cost of culture media. This study investigated the possibility of using loblolly pine and sweetgum autohydrolysates as economic feedstocks for microbial lipid production by oleaginous Rhodococcus opacus (R. opacus) PD630 and DSM 1069. Results revealed that when the substrates were detoxified by the removal of inhibitors (such as HMF-hydroxymethyl-furfural), the two strains exhibited viable growth patterns after a short adaptation/lag phase. R. opacus PD630 accumulated as much as 28.6 % of its cell dry weight (CDW) in lipids while growing on detoxified sweetgum autohydrolysate (DSAH) that translates to 0.25 g/l lipid yield. The accumulation of SCOs reached the level of oleagenicity in DSM 1069 cells (28.3 % of CDW) as well, while being cultured on detoxified pine autohydrolysate (DPAH), with the maximum lipid yield of 0.31 g/l. The composition of the obtained microbial oils varied depending on the substrates provided. These results indicate that lignocellulosic autohydrolysates can be used as low-cost fermentation substrates for microbial lipid production by wild-type R. opacus species. Consequently, the variety of applications for aqueous liquors from lignocellulosic pretreatment has been expanded, allowing for the further optimization of the integrated biorefinery.

Biomass as Raw Material for Production of High‐Value Products

“…These biooils are most commonly used as a replacement for petroleum fuels but they can be also served as feedstock for production of a wide range of value-added products. For instance, lignin-derived phenolics can be converted into aromatic chemicals by hydrogenation [69], and carbohydrates are utilized for catalytic production of hydrogen or consumed in fermentation [70].…”

Utilization of simultaneous saccharification and fermentation residues as feedstock for lipid accumulation in Rhodococcus opacus

“…Though engineered algae and yeast are prominent in the field, the oleaginous soil bacteria in the family Rhodococcus is an emerging candidate for study due to a broader threshold of suitable nutrients and cultivation conditions (Alvarez et al 2000 ; Gomez et al 2016 ; Salvachúa et al 2015 ). In recent years, Rhodococcus opacus ( R. opacus ) strains DSM 1069 and PD630 have been investigated for their ability to accumulate significant amounts of intracellular single cell oils (Kosa and Ragauskas 2011 , 2012 , 2013 ; Wei et al 2015a , b , c ). For example, R. opacus PD630 has been shown to exhibit oleaginicity ~ 80% on a cell dry weight basis (CDW) when glucose was utilized as a carbon source under nitrogen-limited conditions (Alvarez et al 2000 ; Alvarez and Steinbuechel 2002 ).…”

A Review on The Bioconversion of Lignin to Microbial Lipid with Oleaginous Rhodococcus opacus

“…Typically, effluent fractions are discarded as industrial wastewater but here it was shown to be a viable feedstock for the production of microbial lipids possibly due to the increased solubility of lignin compounds. Wei showed that oleaginicity can be improved (28%) when substrates are detoxified by the removal of inhibitors such as hydroxymethyl-furfural [70] (Table 1, #3). Fermentations of Kraft lignin from black liquor by R. opacus also resulted in poor lipid titers (<0.01 mg/ml) and strain oleaginicity [71] suggesting that pretreatments were necessary to improve the properties of Kraft lignin.…”

“…R. opacus can metabolize and degrade aromatic compounds found in lignocellulosic biomass [64] and accumulate intracellular single cell oils [54][55][56][57][58][59]. Rhodococcus strains have been engineered to express enzymes to degrade cellulose [65] and xylose [66].…”

“…Transcriptomic and proteomic studies have also identified TAG biosynthetic genes and proteins [48][49][50][51][52][53]. In previous years, the Gram-positive, oleaginous, soil bacterium Rhodococcus opacus has been studied for its ability to accumulate intracellular lipids >20%, based on cell dry weight (CDW) [54][55][56][57][58][59][60]. Some Rhodococcus strains exhibit oleaginicity above 80% CDW, when glucose is utilized as a carbon source under nitrogen-limited conditions [61,62].…”