The use of response surface methodology for enhanced production of a thermostable bacterial lipase in a novel yeast system

Statistical optimization and sequential scale-up of α-galactosidase production by Actinoplanes utahensis B1 from shake flask to pilot scale

α-Galactosidase (α-GAL) is a class of hydrolase that releases galactose from galacto-oligosaccharides and synthetic substrates such as pNPG. In this study, the production of α-GAL by Actinoplanes utahensis B1 in submerged fermentation was enhanced by using statistical methods. The effects of temperature, pH, and inoculum percentage on enzyme secretion were optimized using BBD of RSM. The optimized process was scaled up from the shake flask to the laboratory scale (5 L) and to pilot scale (30 L) using KLa based scale-up strategy. By using BBD, a maximum yield of 62.5 U/mL was obtained at a temperature of 28 °C, a pH of 6.9, and an inoculum of 6.4%. Scale-up was performed successfully and achieved a yield of 74.4 U/mL and 76.8 U/mL in laboratory scale and pilot scale fermenters. The TOST was performed to validate the scale-up strategy and the results showed a confidence level of 95% for both scales indicating the perfect execution of scale-up procedure. Through the implementation of BBD and scale-up strategy, the overall enzyme yield has been significantly increased to 76%. This is the first article to explore the scale-up of α-GAL from the A. utahensis B1 strain and provide valuable insights for industrial applications.

A Lipase Gene of Thermomyces lanuginosus: Sequence Analysis and High-Efficiency Expression in Pichia pastoris

Lipase, a type of enzyme that decomposes and synthesizes triglycerides, plays an important role in lipid processing. In this study, a heat-resisting lipase gene (lip4) from Thermomyces lanuginosus was subcloned into the pPICZαA vector and then transformed into Pichia pastoris X33. The recombinant yeast cell concentration reached the maximum (119.5 g/L) at 144 h, and the lipase (Lip4) activity reached the maximum (3900 U/mL) at 168 h in 10 L bioreactor. Through bioinformatics analysis, S168, as the key site of Lip4, participated in the formation of the catalytic triads S168-D223-H280 and G166-H167-S168-L169-G170. Furthermore, S168 and seven conserved amino acids of G104/288, S105, A195, P196, V225 and I287 constitute the active center of Lip4. Specifically, the structure modeling showed two α-helices of the lid domain, outside the active pocket domain, controlling the entry of the substrate on Lip4. The potential glycosylation of Asn-33 may be involved in exhibiting the high stable temperature for lipase activity. Therefore, the eukaryotic system was constructed to express Lip4 efficiently, and the amino acid sites related to the catalytic efficiency of Lip4 were clarified, providing a new way for its subsequent property research and industrial application.

Opportunistic yeast pathogen Candida spp.: Secreted and membrane-bound virulence factors

Candidiasis is a fungal infection caused by Candida spp. especially Candida albicans, C. glabrata, C. parapsilosis and C. tropicalis. Although the medicinal therapeutic strategies have rapidly improved, the mortality rate due to candidiasis has continuously increased. The secreted and membrane-bound virulence factors (VFs) are responsible for fungal invasion, damage and translocation through the host enterocytes besides the evasion from host immune system. VFs such as agglutinin-like sequences (Als), heat shock protein 70, phospholipases, secreted aspartyl proteinases (Sap), lipases, enolases and phytases are mostly hydrolases which degrade the enterocyte membrane components except for candidalysin, the VF acts as a peptide toxin to induce necrotic cell lysis. To date, structural studies of the VFs remain underexplored, hindering their functional analyses. Among the VFs, only secreted aspartyl proteinases and agglutinin-like sequences have their structures deposited in Protein Data Bank (PDB). Therefore, this review scrutinizes the mechanisms of these VFs by discussing the VF-deficient studies of several Candida spp. and their abilities to produce these VFs. Nonetheless, their latest reported sequential and structural analyses are discussed to impart a wider perception of the host-pathogen interactions and potential vaccine or antifungal drug targets. This review signifies that more VFs structural investigations and mining in the emerging Candida spp. are required to decipher their pathogenicity and virulence mechanisms compared to the prominent C. albicans.

LAY ABSTRACT

Candida virulence factors (VFs) including mainly enzymes and proteins play vital roles in breaching the human intestinal barrier and causing deadly candidiasis. Limited VFs' structural studies hinder deeper comprehension of their mechanisms and thus the design of vaccines and antifungal drugs against fungal infections.

Efficient production of ε-poly-l-lysine using cassava starch and fish meal by Streptomyces albulus FQC-24

ε-Poly-l-lysine (ε-PL) is used as a natural food preservative which consists of l-lysine units connected. However, due to the expensive culture medium, the production cost of ε-PL remains high. In this study, cheap raw materials cassava starch (CS) and fish meal (FM) were employed by S. albulus FQC-24 for ε-PL production. In the single factor experiment, the maximum ε-PL production reached 0.97 g/L at 60 g/L CS and 15 g/L FM. The results of screening experiments by Plackett-Burman design showed that three main components affecting ε-PL production were CS, FM, and (NH₄)₂SO₄. And the standardized effects of CS, FM, and (NH₄)₂SO₄ were 0.13, -0.22, and -0.2, respectively. The optimum fermentation medium developed by response surface methodology for ε-PL production contained (g/L) CS, 67.56; FM, 14.70 and (NH₄)₂SO₄, 5.41. Under the optimum conditions, the ε-PL production was achieved 1.30 g/L, with 34.02% higher than that before optimization. Moreover, ε-PL productions of batch and fed-batch fermentation in a 7-L fermentor were improved to 2.13 and 17.17 g/L respectively, which increased by 0.64 and 12.2 times compared with the shake flask culture. The results indicated that FM and CS are promising substrates for the efficient production of ε-PL.