Cellulolytic Bacillus strains from natural habitats – A review
Fossil fuel reserves depletion, global warming, costly and problematic waste recycling and population growth greatly induce to find renewable energy sources. Second generation bioethanol produced from lignocellulosic materials exhibits great potential as liquid biofuel to substitute gasoline.
Production costs of enzymes involved in cellulose hydrolysis into fermentable sugars represent the main obstacle to achieve competitive production of cellulosic ethanol. Cheaper and more efficient biocatalysts for the saccharification step are, therefore, required for making the whole process more competitive. The biodiversity of natural niches has been so far exploited for the isolation of new cellulolytic microorganisms whose enzymes are naturally evolved for an efficient conversion of cellulose into fermentable sugars.
This review discusses advances in isolation of bacteria, namely Bacillus spp., from several natural habitats and their ability to produce cellulase activity.
Second generation ethanol, produced from lignocellulosic materials, such as agricultural wastes, plant wastes and other industrial wastes, offers a more attractive greenhouse gas emissions profile than other biofuels, with a 86 % reduction of greenhouse gas emissions in comparison to gasoline (1). Moreover, use of lignocelluloses favors overcoming the so called fuel versus food conflict rising from the use of agricultural products (first generation bioethanol) normally addressed to human diet. The main challenges to improve the whole process associated with the conversion of cellulosic biomass to ethanol include increasing polysaccharides hydrolysis yield, decreasing loading of hydrolytic enzymes, optimizing or eliminating the pretreatment and developing a consolidated bioprocessing where the enzyme production, the hydrolysis step and fermentation of sugars into ethanol occur in a single process (2, 3).
An enormous range of different habitats such as soil, compost piles, decaying plant materials, rumens, sewage sludge, invertebrates like termites (gut), forest waste piles, wood processing plants, leaf litter, animal faces, paper mill ...