Renewable biofuels: extremozymes as innovative biocatalysts for (hemi)cellulosic materials hydrolysis.

Worldwide there is a growing interest in the utilization, for bioenergetic purposes, of lignocellulosic materials, the most abundant and renewable resources on Earth that constitute a large component of the wastes originated from municipal, agricultural, forestry and some industrial sources. The (hemi)cellulosic fraction accounts for about 75% of the lignocellulosic biomasses composition. Its saccharification into fermentable sugars, readily convertable into ethanol, represents a challenging solution for the utilization of these resources in place of fossil fuels. As a matter of fact the production of ethanol from lignocellulosic sources is a promising mean to decrease the accumulation of greenhouse gasses and alleviate pressure on the fossil fuels inevitable depletion. The exploitation of innovative enzymatic bio-processes could be the adequate solution to obtain biofuels from these vegetable biomasses, avoiding environmental problems. However, bio-ethanol production is currently not cost competitive with gasoline and the enzyme production and utilization give the major contributes to the overall costs. So, the main research efforts are directed to improve the saccharification yields exploiting new more performant hydrolytic enzymes also in conjunction with new more effective biomass pretreatment processes. (Hemi)cellulolytic enzymes of microbial origin play an important role in bioconversion processes of lignocellulosic materials. As the enzyme stability at the industrial process conditions is the main requirement for their convenient commercial applications, the extremophilic microorganisms have received considerable attention as sources of highly efficient and stable cellulolytic and hemicellulolytic activities. Enzymes isolated from Bacteria and Archaea that live in environments characterized by extreme conditions, are capable of producing (hemi)cellulolytic enzymes resistant to high temperatures, extreme pH values and presence of organic solvents and denaturing agents. In this scenario, it makes sense to take into account the enzymes derived from bacteria of the genus Bacillus that are regarded as attractive industrial organisms thriving at temperatures also higher than 60°C and alkaline pHs and able to produce huge amounts of a great variety of extracellular enzymes. Our attention has been focused on two strains belonging to Anoxybacillus sp. and Geobacillus thermodenitrificans A333 species respectively due to their interesting xylanolytic activities. In particular a xylosidase was identified and purified from Anoxybacillus sp., a thermophilic microorganism isolated from Azores hot springs at 90°C. The enzyme was characterized by optimal activities at values of temperature and pH which were of 65°C and 5.5 respectively. Geobacillus thermodenitrificans on the other hand showed the production of an endo-xylanase activity that was purified and characterized by our research group. Interestingly the enzyme showed relevant characteristics of resistance to thermo-alkaline conditions and tolerance at high salinity, solvent and surfactant concentrations. Moreover, in a recent screening for cellulolytic microorganisms from Azores hot springs, a bacterial strain identified as Alicyclobacillus sp and exhibiting high level of an extracellular endo-glucanase activity, was isolated. The enzymatic crude extract showed its optimal activity at75°C and pH 4.0 and a relevant stability around these values of temperature and pH. Studies are in progress on the new enzymes that, owing to their stability at extreme process conditions, can be certainly regarded as efficient biocatalysts exploitable in the lignocellulosics biotransformation processes.