Educação científica e sustentabilidade: óxido de grafeno magnético como alternativa aos antibióticos na produção de etanol

Abstract

Antibiotic resistance is a global public health concern that must be addressed. In the production of fuel ethanol, antibiotics are used to control bacterial contaminants that compete with yeast for the substrate, reducing the yield of alcoholic fermentation. However, their use also favors the selection and spread of resistant bacteria, since three to six types of antibiotics are alternated in this process. The problem is exacerbated when production byproducts, which may contain antibiotic residues and resistant bacteria, are reused, including vinasse in soil fertigation and yeast, which after the process is dried and used in feed production. The first chapter deals with general considerations. The second and third chapters aimed to synthesize and characterize graphene oxide (GO) and magnetic graphene oxide (GRAMOX) with antimicrobial activity, for alternative use to antibiotics in ethanol production and to verify conditions for their use in the industrial production process, recyclability, biocompatibility, ability to inhibit biofilms and degrade or adsorb complex biomolecules. To determine their antibacterial activity, through tests to determine the minimum inhibitory concentration (MIC) in planktonic and sessile bacterial forms, frequent contaminating microorganisms in the process, isolated in alcohol plants, were used: enterotoxigenic Escherichia coli, Acetobacter aceti, Lactobacillus delbruekii, Leuconostoc mesenteroides and Clostridium acetobutylicum. The compound characterizations elucidated the stability during synthesis, with evidence of surface modification by scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy demonstrating the presence of magnetic iron and Raman spectroscopy and thermogravimetry explaining the composition, bonds and thermal stability. The MIC showed that all tested species were resistant to penicillin and erythromycin and two were multidrug resistant (MDR). GRAMOX at a concentration of 32 µgmL-1 inhibited all species and significantly prevented biofilm formation. The best conditions for the production of antibiotic-free ethanol were: GRAMOX concentration of 32 µgmL-1, pH in the range of 4 to 6 and temperature of 25ºC to 30ºC, with higher ethanol yield values and lower residual sucrose. GRAMOX was recovered and reused in at least 12 production cycles, with only 0.93% mass loss, and showed biocompatibility in cellular toxicity tests, demonstrating good yield in ethanol production without the use of antibiotics. The fourth chapter refers to the importance of scientific information as a tool for controlling antimicrobial resistance. This is a technical article that presents results obtained in an extension activity on the Zoopage website, which disseminates useful and reliable information in a playful, critical and reflective way, including the rational use of antibiotics. The set of results demonstrated that it is possible to combat resistance with the development of innovative and more sustainable inhibitor products, but also with the dissemination of knowledge, which are ways of contributing to safer ethanol production for human, animal and environmental health.