Genome-wide identification and functional characterization of borneol dehydrogenases in Wurfbainia villosa.

MAIN CONCLUSION: Genome-wide screening of short-chain dehydrogenases/reductases (SDR) family reveals functional diversification of borneol dehydrogenase (BDH) in Wurfbainia villosa. Wurfbainia villosa is an important medicinal plant, the fruits of which accumulate abundant terpenoids, especially bornane-type including borneol and camphor. The borneol dehydrogenase (BDH) responsible for the conversion of borneol to camphor in W. villosa remains unknown. BDH is one member of short-chain dehydrogenases/reductases (SDR) family. Here, a total of 115 classical WvSDR genes were identified through genome-wide screening. These WvSDRs were unevenly distributed on different chromosomes. Seven candidate WvBDHs based on phylogenetic analysis and expression levels were selected for cloning. Of them, four BDHs can catalyze different configurations of borneol and other monoterpene alcohol substrates to generate the corresponding oxidized products. WvBDH1 and WvBDH2, preferred (+)-borneol to (-)-borneol, producing the predominant ( +)-camphor. WvBDH3 yielded approximate equivalent amount of (+)-camphor and (-)-camphor, in contrast, WvBDH4 generated exclusively (+)-camphor. The metabolic profiles of the seeds showed that the borneol and camphor present were in the dextrorotatory configuration. Enzyme kinetics and expression pattern in different tissues suggested WvBDH2 might be involved in the biosynthesis of camphor in W. villosa. All results will increase the understanding of functional diversity of BDHs.

High-solids enzymatic saccharification of starch-rich raw herbal biomass residues for producing high titers of glucose.

The bioresource utilization of herbal biomass residues (HBRs) has been receiving more attention. Herein, three different HBRs from Isatidis Radix (IR) and Sophorae Flavescentis Radix (SFR) and Ginseng Radix (GR) were subjected to batch and fed-batch enzymatic hydrolysis to produce high-concentration glucose. Compositional analysis showed the three HBRs had substantial starch content (26.36-63.29%) and relatively low cellulose contents (7.85-21.02%). Due to their high starch content, the combined action of cellulolytic and amylolytic enzymes resulted in greater release of glucose from the raw HBRs compared to using the individual enzyme alone. Batch enzymatic hydrolysis of 10% (w/v) raw HBRs with low loadings of cellulase (≤ 10 FPU/g substrate) and amylolytic enzymes (≤ 5.0 mg/g substrate) led to a high glucan conversion of ≥ 70%. The addition of PEG 6000 and Tween 20 did not contribute to glucose production. Furthermore, to achieve higher glucose concentrations, fed-batch enzymatic hydrolysis was conducted using a total solid loading of 30% (w/v). After 48-h of hydrolysis, glucose concentrations of 125 g/L and 92 g/L were obtained for IR and SFR residues, respectively. GR residue yielded an 83 g/L glucose concentration after 96 h of digestion. The high glucose concentrations produced from these raw HBRs indicate their potential as ideal substrate for a profitable biorefinery. Notably, the obvious advantage of using these HBRs is the elimination of the pretreatment step, which is typically required for agricultural and woody biomass in similar studies.

Highly efficient glucose production from raw non-pretreated Chinese medicinal herbal residues via the synergism of cellulase and amylolytic enzymes.

Available literature on Chinese medicinal herbal residues (CMHRs) bioconversion highlights pretreatment prior to saccharification with cellulase without considering the presence of starch constituent. Herein, four commonly found CMHRs were tested for starch content, and it was found they all contained starch with content ranging from 4.74% to 16.78%. Hydrolysis of raw CMHRs with combined cellulase and amylolytic enzymes yielded increments of 16.85% to 26.51% in 48-h glucan conversion compared to cellulase alone. Further study showed 48-h glucan conversion of raw CMHRs outperformed that pretreated by water-ethanol successive extraction, ultrasound and acid, but underperformed alkali-pretreated CMHRs. Although increasing 48-h glucan conversion in the range of 7.40% to 24.10% compared to raw CMHRs, alkaline pretreatment demonstrated low glucose recovery and incurred additional cost, making it unfavorable. Saccharification of the four raw CMHRs with combined enzymes seems like a preferred option considering the elimination of high-cost pretreatment step.