No abstract

The authors have withdrawn this preprint due to a need to make corrections.

AgradecimentosA DEUS por me dar vida, saúde e vigor para enfrentar os desafios e porque, sem Ele, não teria chegado até aqui. À minha esposa Valéria, pelo grande amor e carinho ao longo de mais de 6 anos de caminhada juntos, e por tornar meus dias mais agradáveis. Aos meus pais Geraldo e Helena pelo amor, pelo constante apoio, e por não medirem esforços para que todos os filhos estudassem. À Viviane e ao Renato, meus queridos irmãos, por sempre me apoiarem nessa caminhada, pelo carinho, e pelas conversas sempre motivadoras. À minha sogra e aos meus cunhados pelo carinho e pela torcida! À Prof a . Dr a . Glaucia Maria Pastore pela oportunidade desde o mestrado, pela orientação, incentivo e por acreditar no meu trabalho. Ao Dr. Fabio Squina pela oportunidade única de desenvolver o trabalho no CTBE, pela coorientação ao longo de todo o trabalho, pela coordenação das pesquisas no CTBE, e também por confiar no meu trabalho.

BackgroundCommercial yeast strains are a promising alternative to chemical additives in ruminants; but are not self to the rumen ecosystem. In this study, the aim was to identify and evaluate the growth, mass production, and enzymatic activity of yeast strains naturally isolated from bovine rumen in submerged fermentations containing roughages with high concentration of lignocellulose. An experiment was initially conducted to compare the degradation of Urochloa decumbens (UD) hay or sugarcane bagasse (SB) by eight yeast isolates and a control without microorganisms. Subsequently, further experiments were performed to compare the degradation of the two substrates by two yeast strains (V5 and V62) selected (from the eight used in the initial screen) and a control without microorganisms for four different fermentation periods. Results Among the identified strains, Pichia kudriavzevii was the most common, followed by Rhodotorula mucilaginosa and Candida tropicalis. The strain (V5 R. mucilaginosa ) showed higher mass production than other strains of this specie in fermentations with UD (P<0.05). The V5 and V10 and V62 ( Pichia kudriavzevii ) promoted a higher rate of dry matter (DM) reduction of UD than other yeast and strain V5 was the most efficient in dry matter reduction of SB (P <0.05). The V5 and V62 were selected for analyzes of enzyme production, that showed V5 reducing ph at 96 h of fermentation and V62 and V5 increasing pectinase activate at 96 hs of fermentation. However, these isolates did not exhibit expressive xylanase activity under the evaluated fermentation conditions. Conclusion The strain V5 promoted the highest dry matter reduction of sugarcane bagasse and U. decumbens, showing significative yeast biomass production. This yeast and the V62 strain increased the pectinase activities at 96 h of fermentation of U. decumbens showing potential of industrial application and for animal diets. Additionally, V5 strain would be selected and represent potential probiotic for cattle raised in tropical pasture