High NaCl concentrations induce the resistance to thermal denaturation of an extremely halotolerant (salt-activated) β-mannanase from Bacillus velezensis H1

ss-mannanase catalyzes the hydrolysis of mannans ss-1,4-mannosidic linkages to produce industrially relevant oligosaccharides. These enzymes have numerous important applications in the detergent, food, and feed industries, particularly those that are resistant to harsh environmental conditions such as salts and heat. While, moderately salt-tolerant ss-mannanases are already reported, existence of a high halotolerant ss-mannanase is still elusive. This study aims to report the first purification and characterization of ManH1, an extremely halotolerant ss-mannanase from the halotolerant B. velezensis strain H1. Electrospray ionization quadrupole time-of-flight mass spectrometry (ESI-Q-TOF-MS) analysis revealed a single major peak with a molecular mass of 37.8 kDa demonstrating its purity. The purified enzyme showed a good thermostability as no activity was lost after a 48 h incubation under optimal conditions of 50 degrees C and pH 5.5. The enzyme's salt activation nature was revealed when its maximum activity was obtained in the presence of 4 M NaCl, it doubled compared to the no-salt condition. Moreover, NaCl strengthens its resistance to thermal denaturation, as its melting temperature (Tm) increased steadily with increasing NaCl concentrations reaching 75.5 degrees C in the presence of 2.5 M NaCl. The Km and Vmax values were 5.63 mg/mL and 333.33 mu mol/min/mL, respectively, using carob galactomannan (CG) as a substrate. The enzyme showed a significant ability to produce manno-oligosaccharides (MOS) from lignocellulosic biomass releasing 13 mg/mL of reducing sugars from olive mill wastes (OMW) after 24 h incubation. The results revealed that this enzyme may have significant commercial values for agro-waste treatment, and other potential applications.

Automated summary

This study reports the purification and characterization of an extremely halotolerant ss-mannanase ManH1 from B. velezensis strain H1. The enzyme showed good thermostability and salt activation, with increased activity in the presence of NaCl. It also demonstrated the ability to produce oligosaccharides from lignocellulosic biomass, indicating its potential commercial value.