Background: Selenium is an essential trace element that is critical for many biological processes. Selenium nanoparticles (SeNPs) have shown more promise than other forms of selenium due to their low cytotoxicity and high bioavailability. Methods: In this work, a one-step method was demonstrated for fabricating bovine serum albumin (BSA) stabilized SeNPs using ascorbic acid as the reductant. Human dermal fibroblasts were used to assess mammalian cytotoxicity, and Staphylococcus aureus and Escherichia coli were used to assess antibacterial performance. Results: These SeNPs demonstrated increased fibroblast growth and reduced Staphylococcus aureus growth with a fibroblast IC 50 value (>681 μg/mL) 1 order of magnitude higher than that for bacteria at day 1. Conclusion: This study demonstrated the promise of this synthesis process in achieving controllable selenium nanoparticle sizes without the use of strong basic solvents for improved antibacterial properties.

The basidiomycetous yeast Rhodosporidium toruloides is an important chassis organism for producing microbial lipids and terpenoids. However, excess carbon flux flows towards lipid synthesis than terpenoid synthesis. Thus, it is essential to limit lipid accumulation so that R. toruloides can be explored as an advanced cell factory for producing non-lipid derivatives. In this study, we knocked out two lipid droplet (LD) structural proteins (Ldp1 and Cals) of R. toruloides NP11 through the CRISPR/Cas9 system to reduce lipid production. The results showed that lipid content of LD protein-disrupted strains dropped by over 40%. LDP1-disrupted mutants harbored small-sized LDs. This study provided valuable information to study about microbial lipid metabolism and platform strains for constructing advanced cell factories.

The oleaginous yeast Rhodosporidium toruloides has emerged as a robust host for production of microbial lipids as alternative biofuel feedstocks. Oxygen supply is a limiting factor for microbial lipid production, as lipid biosynthesis is highly oxygen-demanding. Vitreoscilla hemoglobin (VHb) is a protein capable of promoting oxygen delivery for anabolism. In this study, we developed R. toruloides with VHb expression for improved lipid production. The VHb expression cassette was integrated into the R. toruloides chromosome via the Agrobacterium-mediated transformation. In shake flask cultures, the engineered strain 4#-13 produced 34% more lipids than the parental strain did. Results obtained under reduced aeration conditions in 3 L bioreactor showed that lipid titer and lipid yield of the engineered strain 4#-13 were 116% and 71%, respectively, higher than those of the parental strain. Under high cell density culture conditions, the engineered strain 4#-13 grew faster and produced 72% more lipids. Our results demonstrated that the VHb gene is functional in R. toruloides for promoting lipid production. The strains described here may be further engineered by integrating extra genetic parts to attain robust producers for more valuable products. This should improve the economics of microbial lipids to facilitate a sustainable production of biodiesel and other lipid-based biofuels.

Mitochondria are semi-autonomous organelles with their own genome and crucial to cellular material and energy metabolism. Here we report the complete mitochondrial genome of a lipid-producing basidiomycetous yeast Rhodotorula toruloides NP11. The mitochondrial genome of R. toruloides NP11 was assembled into a circular DNA molecule of 125937 bp, encoding 15 proteins, 28 tRNAs, 2 rRNA subunits and 10 open reading frames with unknown function. The G + C content (41%) of the mitochondrial genome is substantially lower than that of the nuclear genome (62%) of R. toruloides NP11. Further reanalysis of the transcriptome data confirmed the transcription of 4 mitochondrial genes. The comparison of the mitochondrial genomes of R. toruloides NP11 and NBRC0880 revealed a significant genetic divergence. These data can complement our understanding of the genetic background of R. toruloides and provide fundamental information for further genetic engineering of this strain.