Terpenoids represent the largest class of natural products, some of which are resources for pharmaceuticals, fragrances, and fuels. Generally, mass production of valuable terpenoid compounds is hampered by their low production levels in organisms and difficulty of chemical synthesis. Therefore, the development of microbial biosynthetic platforms represents an alternative approach. Although microbial terpenoid-production platforms have been established in Escherichia coli and yeast, an optimal platform has not been developed for Streptomyces species, despite the large capacity to produce secondary metabolites, such as polyketide compounds. To explore this potential, we constructed a terpenoid-biosynthetic platform in Streptomyces reveromyceticus SN-593. This strain is unique in that it harbors the mevalonate gene cluster enabling the production of furaquinocin, which can be controlled by the pathway specific regulator Fur22. We simultaneously expressed the mevalonate gene cluster and subsequent terpenoid-biosynthetic genes under the control of Fur22. To achieve improved fur22 gene expression, we screened promoters from S. reveromyceticus SN-593. Our results showed that the promoter associated with rvr2030 gene enabled production of 212 ± 20 mg/L botryococcene to levels comparable to those previously reported for other microbial hosts. Given that the rvr2030 gene encodes for an enzyme involved in the primary metabolism, these results suggest that optimized expression of terpenoid-biosynthetic genes with primary and secondary metabolism might be as important for high yields of terpenoid compounds as is the absolute expression level of a target gene(s).
Non-conventional yeasts have an untapped potential to expand biotechnology and enable process development necessary for a circular economy. They are especially convenient for the field of lipid and hydrocarbon biotechnology because they offer faster growth than plants, easier scalability than microalgae and exhibit increased tolerance relative to some bacteria. The ability of industrial organisms to import and metabolically transform lipids and hydrocarbons are crucial in such applications. Here, we assessed the ability of 14 yeasts to utilize 18 model lipids and hydrocarbons from six functional groups and three carbon chain lengths. The studied strains covered 12 genera from nine families. Nine non-conventional yeast performed better than Saccharomyces cerevisiae, the most common industrial yeast. Rhodotorula toruloides, Candida maltosa, Scheffersomyces stipis and Yarowia lipolytica were observed to grow significantly better and on more types of lipid and lipid-molecules than other strains. They were all able to utilize mid to long-chain fatty acids, fatty alcohols, alkanes, alkenes and dicarboxylic acids, including 28 previously unreported substrates across the four yeasts. Interestingly, a phylogenetic analysis showed a short evolutionary distance between the R. toruloides and C. maltosa and S. stipitis, even though R. toruloides is classified under a different phylum. This work provides valuable insight into the lipid substrate range of non-conventional yeasts that can inform species selection decisions and viability of lipid feedstocks.
On extended screening of squalene-producing strains in Okinawa mangrove water, we identified 14 novel squalene-producing thraustochytrids from 172 unialgal clonal isolates. The novel thraustochytrids produced 13.9-7.54 mg squalene/g dry cell weight. Eight isolates were found to belong to potentially novel squalene-producing genera, forming a monophyletic cluster independent from any known thraustochytrids.
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