Emerging platforms for co-utilization of one-carbon substrates by photosynthetic organisms.

One-carbon substrates have generated increasing attention as long-term sustainable feedstocks for biobased production of fuels and chemicals. However, their physicochemical properties present significant biological and operational challenges for commercial bioprocesses including kinetically slower substrate activation, high energetic cost of assimilation, low mass transfer, substrate toxicity, and low productivity titers. Several different routes including optimization of native pathways, synthetic pathways, and hybrid methods are being explored to overcome these challenges. Integration of emerging biological solutions with process improvements is enabling faster bioprocess development for cost-effective conversion of one-carbon substrates into fuels and chemicals.

Expression of a Streptomyces 3-hydroxysteroid oxidase gene in oilseeds for converting phytosterols to phytostanols.

Plant sterols and their hydrogenated forms, stanols, have attracted much attention because of their benefits to human health in reducing serum and LDL cholesterol levels, with vegetable oil processing being their major source in several food products currently sold. The predominant forms of plant sterol end products are sitosterol, stigmasterol, campesterol and brassicasterol (in brassica). In this study, 3-hydroxysteroid oxidase from Streptomyces hygroscopicus was utilized to engineer oilseeds from rapeseed (Brassica napus) and soybean (Glycine max), respectively, to modify the relative amounts of specific sterols to stanols. Each of the major phytosterols had its C-5 double bond selectively reduced to the corresponding phytostanol without affecting other functionalities, such as the C-22 double bond of stigmasterol in soybean seed and of brassicasterol in rapeseed. Additionally, several novel phytostanols were obtained that are not produced by chemical hydrogenation of phytosterols normally present in plants.