Avaliação funcional e potencial biotecnológico da água residuária de agroindústrias de mandioca: do isolamento à análise metagenômica

Abstract

Cassava is recognized as an agricultural crop of great importance in Brazil, which generates by-products with a high organic load. The toxicity of the wastewater associated with cassava processing is limited to the excess of organic compounds and sugars and the presence of cyanoglycosides, which pose environmental risks if not adequately treated. However, this wastewater has significant potential as a source of nutrients and bioactive compounds for sustainable biotechnological applications, mitigating adverse environmental impacts. This study evaluated wastewater samples from two cassava processing agro-industries: a starch processor (ARFe) and a flour processor (ARFa). The aim was to investigate this waste's microbial composition and biotechnological potential using microbiological isolation methods, metagenomics, and functional tests. In article 1, bacterial isolates were obtained using the serial dilution and isolation method, followed by morphological and Gram stain characterization and physiological characterization regarding biological nitrogen fixation, phosphate and potassium solubilization, and siderophore synthesis. A total of 182 bacterial isolates were obtained, which demonstrated functional capacities relevant to agriculture, including a high rate of nitrogen fixation, phosphate and potassium solubilization, and siderophore production, especially in the ARFa isolates, which indicates potential for the development of biofertilizers. Article 2 carried out a metagenomic analysis of wastewater, which revealed a predominance of the Proteobacteria, Bacteroidota, and Firmicutes phyla, with a greater abundance of the Gemmatimonas, Nannocystis, and Bacillus genera. Despite the chemical variations between the samples, the taxonomic and functional profiles remained stable from 2022 to 2024. The significant correlation between functional diversity and substrate availability reinforces the direct impact of the physicochemical factors of each wastewater on the microbial structure and metabolic behavior of the microorganisms. In the third article, fermentation experiments were carried out using wastewater as a substrate for the bacterium Priestia aryabhattai (CCMMIAB UNIO423) to produce indole-3-acetic acid (IAA) under different supplementation conditions (S1 and S2). Both samples sustained exponential microbial growth; ARFa showed faster initial growth, followed by a decline associated with nutrient depletion, while ARFe showed more stable and prolonged growth over time. S2 supplementation (casein, urea, sucrose, and potassium phosphate) resulted in greater cell viability compared to S1 (glycerol, ammonium nitrate, and yeast extract), with a high production of indole-3-acetic acid (IAA), especially in ARFa. The results indicate the biotechnological potential of cassava wastewater for applications in bioremediation and the production of biofertilizers. The study reinforces the feasibility of using these effluents as a substrate for the growth of plant growth-promoting microorganisms, which contributes to reducing environmental impact and promotes sustainability in agricultural production chains.