A natural consortium of thermophilic bacteria from Huancarhuaz hot spring (Ancash-Peru) for promising lignocellulose bioconversion

The lignocellulose bioconversion process is an eco-friendly and green-economy alternative technology that allows the reduction of pollution and global warming, so it is necessary for thermophilic and thermostable hydrolytic enzymes from natural sources. This research aimed to isolate cellulolytic and xylanolytic microbial consortia from Huancarhuaz hot spring (Peru) from sludge or in situ baiting cultured with or without sugarcane bagasse. According to the hydrolytic activities consortium T4 from in situ baiting was selected. It was cultivated in submerged fermentation at 65 °C, pH 6.5 for eight days using LB supplemented with sugar cane bagasse (SCB), pine wood sawdust (PWS), CMC, xylan of birchwood, or micro granular cellulose. Crude extract of culture supplemented with SCB (T4B) showed better endoglucanase and xylanase activities with higher activities at 75 °C and pH 6. In these conditions, cellulase activity was kept up to 57% after 1 h of incubation, while xylanase activity was up to 63% after 72 h. Furthermore, this crude extract released reduced sugars from pretreated SCB and PWS. According to metagenomic analysis of 16S rDNA, Geobacillus was the predominant genus. It was found thermostable genes: a type of endoglucanase (GH5), an endo-xylanase (GH10), and alkali xylanase (GH10) previously reported in Geobacillus sp. strains. Finally, Huancarhuaz hot spring harbors a genetic microbial diversity for lignocellulosic waste bioconversion in high temperatures, and the T4B consortium will be a promising source of novel extreme condition stable enzymes for the saccharification process.

Characteristics of recombinant xylanase from camel rumen metagenome and its effects on wheat bran hydrolysis

In the present study, we explored the effects of a novel xylanase from camel rumen metagenome (CrXyn) on wheat bran hydrolysis. CrXyn was heterologously expressed in Escherichia coli and showed maximum activity at 40 °C and pH 7.0. Furthermore, CrXyn exhibited preferential hydrolysis of xylan, but no obvious activity toward other substrates, including carboxymethylcellulose and Avicel. Using wheat straw xylan as a substrate, the Km and Vmax values for CrXyn were 5.98 g/L and 179.9 μmol xylose/min/mg protein, respectively. Mn²⁺ was a strong accelerator and significantly enhanced CrXyn activity. However, CrXyn activity was inhibited (~50 %) by 1 mM and 5 mM ethylenediaminetetraacetic acid (EDTA) and completely inactivated by 5 mM Cu²⁺. CrXyn tolerated 5 mM sodium dodecyl sulphate (SDS) and 15 % methanol, ethanol, and dimethyl sulfoxide (DMSO), with >50 % residual activity. CrXyn effectively hydrolyzed wheat bran, with xylobiose and xylotetraose accounting for 79.1 % of total sugars produced. A remarkable synergistic effect was found between CrXyn and protease, leading to an obvious increase in amino acids released from wheat bran compared with the control. CrXyn also enhanced the in vitro hydrolysis of wheat bran. Thus, CrXyn exhibits great potential as a feed additive to improve the utilization of wheat bran in monogastric animal production.

Biochemical characterization of the xylan hydrolysis profile of the extracellular endo-xylanase from Geobacillus thermodenitrificans T12

BACKGROUND

Endo-xylanases are essential in degrading hemicellulose of various lignocellulosic substrates. Hemicellulose degradation by Geobacillus spp. is facilitated by the hemicellulose utilization (HUS) locus that is present in most strains belonging to this genus. As part of the HUS locus, the xynA gene encoding an extracellular endo-xylanase is one of the few secreted enzymes and considered to be the key enzyme to initiate hemicellulose degradation. Several Geobacillus endo-xylanases have been characterized for their optimum temperature, optimum pH and generation of degradation products. However, these analyses provide limited details on the mode of action of the enzymes towards various substrates resulting in a lack of understanding about their hydrolytic potential.

RESULTS

A HUS-locus associated gene (GtxynA1) from the thermophile Geobacillus thermodenitrificans T12 encodes an extracellular endo-xylanase that belongs to the family 10 glycoside hydrolases (GH10). The GtxynA1 gene was cloned and expressed in Escherichia coli. The resulting endo-xylanase (termed GtXynA1) was purified to homogeneity and showed activity between 40 °C and 80 °C, with an optimum activity at 60 °C, while being active between pH 3.0 to 9.0 with an optimum at pH 6.0. Its thermal stability was high and GtXynA1 showed 85% residual activity after 1 h of incubation at 60 °C. Highest activity was towards wheat arabinoxylan (WAX), beechwood xylan (BeWX) and birchwood xylan (BiWX). GtXynA1 is able to degrade WAX and BeWX producing mainly xylobiose and xylotriose. To determine its mode of action, we compared the hydrolysis products generated by GtXynA1 with those from the well-characterized GH10 endo-xylanase produced from Aspergillus awamori (AaXynA). The main difference in the mode of action between GtXynA1 and AaXynA on WAX is that GtXynA1 is less hindered by arabinosyl substituents and can therefore release shorter oligosaccharides.

CONCLUSIONS

The G. thermodenitrificans T12 endo-xylanase, GtXynA1, shows temperature tolerance up to 80 °C and high activity to a variety of xylans. The mode of action of GtXynA1 reveals that arabinose substituents do not hamper substrate degradation by GtXynA1. The extensive hydrolysis of branched xylans makes this enzyme particularly suited for the conversion of a broad range of lignocellulosic substrates.