Engineering Rhodosporidium toruloides for production of 3-hydroxypropionic acid from lignocellulosic hydrolysate.

Microbial production of valuable bioproducts is a promising route towards green and sustainable manufacturing. The oleaginous yeast, Rhodosporidium toruloides, has emerged as an attractive host for the production of biofuels and bioproducts from lignocellulosic hydrolysates. 3-hydroxypropionic acid (3HP) is an attractive platform molecule that can be used to produce a wide range of commodity chemicals. This study focuses on establishing and optimizing the production of 3HP in R. toruloides. As R. toruloides naturally has a high metabolic flux towards malonyl-CoA, we exploited this pathway to produce 3HP. Upon finding the yeast capable of catabolizing 3HP, we then implemented functional genomics and metabolomic analysis to identify the catabolic pathways. Deletion of a putative malonate semialdehyde dehydrogenase gene encoding an oxidative 3HP pathway was found to significantly reduce 3HP degradation. We further explored monocarboxylate transporters to promote 3HP transport and identified a novel 3HP transporter in Aspergillus pseudoterreus by RNA-seq and proteomics. Combining these engineering efforts with media optimization in a fed-batch fermentation resulted in 45.4 g/L 3HP production. This represents one of the highest 3HP titers reported in yeast from lignocellulosic feedstocks. This work establishes R. toruloides as a host for 3HP production from lignocellulosic hydrolysate at high titers, and paves the way for further strain and process optimization towards enabling industrial production of 3HP in the future.

Role and influence of extracellular polymeric substances on the preparation of aerobic granular sludge.

Due to the important role of the extracellular polymeric substances in the formation of aerobic granular sludge, the variation of the EPS contents in the process of cultivation and that in the one running cycle time were studied in this work. Aerobic granules with diameters between 0.8 and 1.1 mm were obtained within 30-35 days. The results suggested that the increase of EPS contents significantly contributed to the formation of aerobic granules. A linear relationship between the EPS and SVI was also developed, and it revealed that the aerobic granules had good settling property when the EPS exceeded 200 mg/g MLVSS. Two mainly components of EPS, protein (PN) and polysaccharides (PS), could act as the endogenous food for the microbes during the starvation period. The survival of the microbial population was jeopardized when the F/M ration was below 0.5 g COD/g SS d.

Injectable in situ cross-linking hyaluronic acid/carboxymethyl cellulose based hydrogels for drug release.

A series of injectable in situ cross-linking hyaluronic acid/carboxymethyl cellulose based hydrogels (HA/CMC) was prepared via disulfide bonds by the oxidation of dissolved oxygen. The results showed that HA/CMC hydrogels exhibited tunable gelling time, appropriate rheology properties, high swelling ratio, good stability, and sustained drug release ability. The gelling time of HA/CMC hydrogels ranged from 1.4 to 7.0 min, and the values of the storage modulus, complex shear modulus, dynamic viscosity, and yield stress of HA3/CMC3 hydrogel were about 5869 Pa, 5870 Pa, 587 Pa·s, and 1969 Pa, respectively. The degradation percentage of HA1/CMC1, HA2/CMC2, and HA3/CMC3 hydrogels were about 60, 49, and 41% after incubating 42 days, and the in vitro cumulative release percentage of BSA from HA1/CMC1, HA2/CMC2, and HA3/CMC3 drug-loaded hydrogels were about 99, 91, and 82% after 30 days. The series of injectable in situ cross-linking HA/CMC hydrogels exhibited good comprehensive performance, signifying that these hydrogels could be potentially used in the fields of short- and medium-term controlled drug release, cell encapsulation, regenerative medicine, and tissue engineering.