Seleção e imobilização de consórcios de bactérias hidrocarbonoclásticas e produtoras de compostos ativos de superfície para aplicações em processos de biorremediação

Abstract

The northern region of Todos os Santos Bay (TSB) mangrove is chronically contaminated by recalcitrant petroleum hydrocarbons. Among the initiatives to mitigate the environmental impacts in this mangrove, the RECUPETRO network (Rede Cooperativa em Recuperação de Areas Contaminadas por Atividades Petrolíferas) was created in 2001, supported by Petrobras and FINEP, aiming at developing bioremediation processes. One of those processes involved the use of bacterial consortia able to degrade hydrocarbons and produce surface active compounds (SACs) immobilized on chitosan. In order to isolate bacterial consortia, we chose the enrichment technique using petroleum, kerosene, hexadecane or a mixture of three polycyclic aromatic hydrocarbons (PAHs), where the cultures growth was confirmed by turbidity and viable cell counts. The enrichment using PAHs was also monitored by Denaturing Gradient Gel Electrophoresis (DGGE) in order to investigate the bacterial population dynamics during 45 days of enrichment. The microorganisms of each consortium were identified by sequencing the gene encoding rRNA16S and evaluated for resistance to the immobilization process on chitosan and SACs production. The chitosan beads obtained were analyzed by scanning electron microscopy (SEM). Microcosms bioremediation assays using contaminated sediments from TSB were carried out using the bacterial consortium isolated from petroleum enrichment and its performance was evaluated by bacterial cell counts and DGGE. The biodegradation efficiency was also measured by gas chromatography. As results of this study, it was obtained 39 bacterial isolates belonging to 20 different genera. The micro-organisms were able to grow using petroleum or its derivatives as carbon sources and to produce SACs (biosurfactant, bioemulsifier and biodemulsifier). Consortia were successfully entrapped in chitosan beads and the SEM confirmed the presence of surface pores, which are essential to the product functionality. In bioremediation experiments using microcosm, the entrapment of consortium within the beads allowed cell growth up to 15 days. At this point, the beads were disintegrated and the biomass was released to the sediment, being the bioaugmentation confu-med by DGGE. The chitosan matrix showed prebiotic activity in the indigenous bacterial communities. Therefore, the beads containing immobilized bacteria contemplate the processes of bioaugmentation and biostimulation. Despite the confirmed bioaugmentation in microcosms, it was not detected significant reductions in the measured pollutants after 90 days of experiment, proving that only the increase in cell number was not sufficient to reduce recalcitrant contaminants at TSB under the experimental conditions adopted.