Production, characterization and techno-economic evaluation of Aspergillus fusant l-asparaginase

Abstract

Protoplast fusion is one of the most reliable methods of introducing desirable traits into industrially-promising fungal strains. It harnesses the entire genomic repertoire of fusing microorganisms by routing the natural barrier and genetic incompatibility between them. In the present study, the axenic culture of a thermo-halotolerant strain of Aspergillus candidus (Asp-C) produced an anti-leukemic l-asparaginase (l-ASNase) while a xylan-degrading strain of Aspergillus sydowii (Asp-S) produced the acrylamide-reduction type. Protoplast fusion of the wild strains generated Fusant-06 with improved anti-leukemic and acrylamide reduction potentials. Submerged fed-batch fermentation was preferred to batch and continuous modes on the basis of impressive techno-economics. Fusant-06 l-ASNase was purified by PEG/Na+ citrate aqueous two-phase system (ATPS) to 146.21-fold and global sensitivity analysis report revealed polymer molecular weight and citrate concentration as major determinants of yield and purification factor, respectively. The enzyme was characterized by molecular weight, amino acid profile, activity and stability to chemical agents. Michaelis–Menten kinetics, evaluated under optimum conditions gave Km, Vmax, Kcat, and Kcat/Km as 6.67 × 10–5 M, 1666.67 µmolmin−1 mg−1 protein, 3.88 × 104 min−1 and 5.81 × 108 M−1.min−1 respectively. In-vitro cytotoxicity of HL-60 cell lines by Fusant-06 l-ASNase improved significantly from their respective wild strains. Stability of Fusant-06 l-ASNase over a wide range of pH, temperature and NaCl concentration, coupled with its micromolar Km value, confers commercial and therapeutic value on the product. Free-radical scavenging and acrylamide reduction activities were intermediate and the conferred thermo-halo-stability could be exploited for sustainable clinical and food industry applications.

Engineering and Expression Strategies for Optimization of L-Asparaginase Development and Production

“…To overcome this problem, a variety of molecular tools and techniques are available for high-level expression of heterologous L-ASNases, including the design of expression plasmids, engineered production hosts, and growth and culture strategies [68]. The use of both naturally occurring hyperproductive strains and those created through genetic engineering, in particular CRISPR/Cas9 systems, protoplast fusion, and response surface methodology, as well as the design of experiments using artificial neural networks and response surfaces, has significantly increased yields [69,70]…”