Avaliação dos efeitos causados por contaminações bacterianas em fermentações etanólicas de primeira geração utilizando metodologias multi-ômicas

Abstract

Multi-omics analyzes of bacterial contaminations in first-generation ethanolic fermentations Ethanol has great strategic importance for the Brazilian energy sector due to its renewable nature and great capacity to generate jobs and income. Currently, one of the main challenges faced by the Brazilian ethanol industry is the presence of contaminating bacteria in the fermentation tanks. They act by modifying the system, competing for essential nutrients, producing toxic compounds to the yeast and inducing undesirable processes for the industry like flocculation. To better balance populations and to control the negative effects, it is necessary a better understanding of the genetic and physiological mechanisms involved in the interactions among bacteria and yeasts from Saccharomyces cerevisiae. In this sense, the present work carried out the sequencing, assembly and complete genome annotation of three bacterial strains isolated directly from Brazilian ethanol production plants: Lactobacillus sp. I-2, Lactobacillus sp. L-10 and Acetobacter sp. A-3. In addition, simulations of the coexistence condition between lactic and acetic bacteria with yeasts from S. cerevisiae were carried out in semi-industrial fed-batch (Melle-Boinot) fermentations with acid treatment and cell recycling. Three experimental conditions were evaluated: (i) fermentations containing only yeasts from S. cerevisiae CAT-1, (ii) fermentations containing yeasts of S. cerevisiae CAT-1 and bacteria from Lactobacillus sp. I-2, and (iii) fermentations containing yeasts from S. cerevisiae CAT-1 and bacteria from Acetobacter sp. A-3. Finally, the metabolomes of bacteria and yeasts in the coexistence condition on fermentation assays were obtained by gas chromatography coupled to mass spectrometry (GC-MS) and liquid chromatography coupled to mass spectrometry (LC-MS). 3056, 2112 and 3557 genes were identified in the genomes of Lactobacillus sp. I-2, Lactobacillus sp. L-10 and Acetobacter sp. A-3, respectively. The yeasts from S. cerevisiae, regardless of the experimental condition evaluated, all the total reducing sugars (ART) present in sugarcane molasses were consumed and the ethanol production was consistent with that observed in first generation (1G) ethanolic fermentations. Glycine, an apolar amino acid containing only one hydrogen in the lateral chain, showed greater abundance during fermentations contaminated with lactic and acetic bacteria. It is speculated that the intracellular accumulation of this amino acid results from the shift of intermediates from the Glycolysis/Glycogenogenesis and the Citric Acid Cycle pathways to the production of nitrogen compounds. Probably, both microorganisms, bacteria and yeasts, used the intracellular accumulation of glycine as an alternative to nitrogen deficiency in sugarcane molasses in the fermentations carried out in bioreactors. The Bacterial genomes sequencing and fermentation assays in bioreactors were performed at the Brazilian Bioethanol Science and Technology Laboratory (CTBE) of the Brazilian Center for Rese...