Resumo

The use of biological processes for removing contaminants is a promising technology based on relatively simple, less aggressive and more suitable methods that contribute to the maintenance of ecological balance. Compared to other alternatives they are considered of low cost. The search for potential microorganisms for environmental application has opened ways for the development of "screening" techniques, such as that based on the redox indicator 2,6-dichlorophenol indophenol (DCPIP), which acting as an electron acceptor may indicate microbial hydrocarbon oxidation. In liquid medium, DCPIP changes from blue (oxidized form) to colorless (reduced form). Thus, this technique has been used to test the biodegradability of various organic molecules and their combinations. In the scope of an investigation on the use of filamentous fungi for degrading BTEX (benzene, toluene, ethyl benzene and xylene), an adaptation of the DCPIP technique was developed in combination with a sensitivity plate test. Fungal cultures were previously cultured on 2% Malt broth to serve as inoculum. After 7 days at 28 °C, 1.0 mL of each culture was transferred for a 96- deepwell plate. To ensure a suitable area for fungal growth on solid medium and to prevent the appearance of false positives, inoculation of the plate was alternated, resulting in a final analysis of 24 isolates per test. Using a replicator, the innocula were transferred to 15 cm diameter Petri dishes containing agar Bushnell Haas (BH) - Difco ™ plus 1 g/L DCPIP and 0.1% toluene as sole carbon source, and incubated at 28 °C. The results were observed every 72 hours. Among the tested strains, 12 showed toluene biodegradation activity, expressed by the formation of a colorless halo (reduced) contrasting with the blue color (oxidized) of the control. The color change of DCPIP in agar proved to be as efficient as that observed previously in the liquid medium with the advantage of providing a greater number of tests in a single board, simultaneously. It is concluded that the sensitivity plate test allied with the biodegradability test (DCPIP) is effective, convenient and quick, because provided a considerable number of results optimizing the reagent use, time and space.