Isolamento e caracterização de leveduras capazes de utilizar o hidrolisado hemicelulósico como fonte de carbono

Abstract

The agro-industrial waste is renewable sources of carbon and energy and can be used for the production of food, feed, chemical compounds, and fuels liquids. The Brazil generates various agro-industrial waste, including the bagasse sugarcane It is the most abundant. This lignocellulosic biomass is rich in carbohydrates metabolizable an economically viable, provided there is adequate hydrolysis material. The deranged hydrolysis the fibers of the three majority polymers of plant biomass (Cellulose, hemicellulose and lignin), making them more accessible to hydrolytic enzymes microbial. This process, in addition to releasing the monomers and small saccharides fermentable, generates inhibitors of microbial growth and fermentation of the material hydrolyzate. The monomers generated by the hydrolysis of hemicellulose fraction are not composed solely of glucose such as starch and cellulosic substrates. They contain, among others wide concentration of pentoses which are not metabolized by all microorganisms. Aiming to get yeast with attributes needed to use the biomass, emphasizing the hemicellulose fraction, investigated the following rich sources of natural hydrolysates: faeces and saliva of ruminants (cattle), as well as digestive tubes immature insects that feed on wood. The culture media used for isolation and cultivation (solid and liquid) were made with hydrolyzed hemicellulose bagasse from sugarcane, obtained by acid hydrolysis. Microorganisms isolates were selected based on their characteristics of use pentose xylose (majority in hemicellulose) and arabinose, aimed at better use of lignocellulosic biomass. 237 were isolated colonies of unicellular microorganisms, through selective. Of these, 231 colonies were subjected to sugar assimilation tests, among which 125 were able to grow using hydrolyzed hemicellulose, xylose or arabinose as carbon source. They stood out, as growth in size, 57 colonies were selected and had the ITS1 - 5.8S rDNA sequenced. After selection for biomass accumulation in a sequenced yeast was chosen and investigated, by response surface methods for optimizing the production of biomass Microbial from hemicellulose hydrolyzate. The sequenced strains formed 05 different groups in the phylogenetic tree and had high similarity with Meyerozyma caribbica, Meyerozyma guilliermondi, micotoxinivorans Trichosporon, Trichosporon loubieri, Pichia kudriavzevii, Candida ethanolic lignohabitants and Candida. A strain with 99% similarity to Meyerozyma caribbica, isolated from bovine feces, accumulated 14,21g / L biomass in 72h in simple batch cultivation type (using instrumented fermenter), being able to tolerate up to 90% hemicellulose hydrolyzate in dry biomass accumulation around 12,43g / L, (Qx = 0.44g / L-1 h-1) after 27 hours cultivation experiments with conical bottles. This yeast produced 14,8g / L xylitol (Qxilt = 0.55 g / L-1h-1) 27 hours of cultivation.