Bioprospecting thermophilic glycosyl hydrolases, from hot springs of Himachal Pradesh, for biomass valorization

Abstract

The harnessing of biocatalysts from extreme environment hot spring niche for biomass conversion is significant and promising owing to the special characteristics of extremozymes attributed by intriguing biogeochemistry and extreme conditions of these environments. Hence, in the present study 38 bacterial isolates obtained from hot springs of Manikaran (~ 95 °C), Kalath (~ 50 °C) and Vasist (~ 65 °C) of Himachal Pradesh were screened for glycosyl hydrolases by in situ enrichment technique using lignocellulosic biomass (LCB). Based on their hydrolytic potential 5 isolates were selected and they were Bacillus tequilensis (VCB1, VCB2 and VSDB4), and B. licheniformis (KBFB2 and KBFB3). Cellulolytic activity assayed by growth under submerged fermentation showed that B. tequilensis VCB1 had maximum FPA activity (3.38 IU ml−1) in 48 h, while B. licheniformis KBFB3 excelled for endoglucanase (EGA of 4.81 IU ml−1 in 24 h) and cellobiase (0.71 IU ml−1 in 48 h) activities. Among all the thermophilic biocatalysts evaluated, highest exoglucanase (0.06 IU ml−1) activity was observed in B. tequilensis VSDB4 while endoglucanase of B. licheniformis KBFB3 showed optimum specific activity at pH 7 and 70 °C. Further, the presence of celS, celB and xlnB genes in the isolates suggest their possible role in biomass conversion. Protein profiling by SDS-PAGE analysis revealed that cellulase isoforms migrated with molecular masses of 75 kDa. The endoglucanase activity of promising strain B. licheniformis KBFB3 was enhanced in the presence of Ca2+, mercaptoethanol and sodium hypochlorite whereas moderately inhibited by Cu2+, Zn2+, urea, SDS and H2O2. The results of this study indicate scope for the possible development of novel biocatalysts with multifunctional thermostable glycosyl hydrolases from hot springs for efficient hydrolysis of the complex lignocellulosic biomass into simple sugars and other derived bioproducts leading to biomass valorization.Electronic supplementary materialThe online version of this article (10.1186/s13568-018-0690-4) contains supplementary material, which is available to authorized users.

Thermotolerant glycosyl hydrolases-producing Bacillus aerius CMCPS1 and its saccharification efficiency on HCR-laccase (LccH)-pretreated corncob biomass

“…However, celS was not found in B. aerius CMCPS1. Our previous finding [21] confirmed the presence of cellulose-binding operons of size 250 bp (celS) domain in thermophilic bacterial strains of B. tequilensis isolated from the hot springs of Himachal Pradesh. In addition, the β-glucosidase-specific primers generated a significant amplicon size of 1500 bp, which further confirmed the presence of multidomain GH-encoding operons.…”

“…In the present study, the GHs were extracellular, as evidenced by the agarose cell diffusion assay. Hence, these endoglucanases could be bound to cells and may be exoenzymes, as observed in our previous report [21] and by Li et al [29].…”

“…Partial purification of cell-free culture supernatant of CMCPS1 revealed multiple banding patterns, which could be attributed to endoglucanases of cytoplasm, endoglucanases from periplasm, or aryl-β glucosidase II [21]. In the present study, the GHs were extracellular, as evidenced by the agarose cell diffusion assay.…”

“…Furthermore, an enhanced endoglucanase production by Bacillus aerius S52 on mixed lignocellulosic substrates was attempted [20]. However, there exist no previous reports of thermophilic B. aerius producing the thermotolerant cellulase, as the majority were reported in B. licheniformis and B. subtilis [2,21]. It is crucial to determine the GHs of thermophilic bacterium B. aerius CMCPS1 on substrates, such as filter paper, CMC, Avicel, and cellobiose.…”

“…In the present study, B. aerius CMCPS1 produced all three cellulases: endoglucanase (2.0 IU mL −1 ), exoglucanase (1.5 IU mL −1 ), and β-glucosidase (1.0 IU mL −1 ) at 48 h under submerged fermentation. Before this, a variety of thermophilic bacteria were identified as GH producers, including B. circulans [22], B. subtilis [23], B. licheniformis, and B. tequilensis [21]. Higher levels of aryl II β-glucosidase activity was found on cellulose than aryl III β-glucosidase activity.…”