Novel cold temperature active β-glucosidase from Pseudomonas lutea BG8 suitable for simultaneous saccharification and fermentation

Abstract

Cold tolerant microbes play a pivotal role in the decomposition of cellulosic biomass in temperate environments. This study was aimed to evaluate β-glucosidase production from psychrotolerant microorganisms isolated from cold desert soil of the Kargil district, Himalayan region, India. A total of 12 morphotypes were isolated at 4 °C and, based on qualitative screening, seven isolates were selected for molecular identification and phenotypic microarray. Pseudomonas lutea BG8 was selected based on its β-glucosidase production potential. The characterization of β-glucosidase revealed the alkali-tolerant nature of the enzyme with a temperature optimum at 40 °C and ability to retain considerable activity over a broad pH range (5–10). The enzyme retained 95.15% activity even in the presence of 1000 mM glucose, indicating an absence of feedback inhibition and high glucose tolerance. The enzyme stability experiment revealed that the β-glucosidase enzyme retained 49.96% activity at pH 5 and 30 °C after 16 h of incubation. The K_m and k_cat of the β-glucosidase enzyme were found to be 0.636 ± 0.103 mM and 102.7 ± 0.004 s⁻¹, respectively. The cold temperature active β-glucosidase from P. lutea BG8 was found to be highly efficient for bioconversion of cellobiose to ethanol along with S. cerevisiae by simultaneous saccharification and fermentation process with 91.42% (0.49 g ethanol per g cellobiose) fermentation efficiency at 4 °C. This novel β-glucosidase can lead to considerable energy savings due to its lower temperature optimum, as compared to commercial β-glucosidase.