Avaliação do crescimento dos fungos Geotrichum candidum Link. & Pers. e Phanerochaete chrysosporium Burds., em cultivos contendo compostos recalcitrantes

Abstract

Effluents with high concentration of organic matter and xenobiotic compounds, especially in the case of the agrochemicals, cause environmental concern. In the present work, the adaptative ability of two filamentous fungi, which cause white rot (Geotrichum candidum Link & Pers. and Phanerochaete chrysosporium Burds.), to tolerate high concentration of xenobiotic substances was analyzed. In solid medium, P. chrysosporium and G. candidum presented excellent development under aerated and not aerated conditions (30ºC and dark), in potato-dextrose-agar and malt extract-agar, respectively. In liquid medium, the same was observed in broth-potato-dextrose and malt extract. The fungi also developed well in liquid media deficient in proteins and carbohydrates, but with high concentrations (10 and 25 mg/L) of the agrochemicals Boral, Decanote, Gliphosate, Paraquat and Plenum - all used in fields of sugar-cane, as the ones of the "S.A Usina Coruripe Açúcar e Álcool" (Coruripe - AL). These chemicals are classified as persistent, belong to the toxicological classes II and III, and have different solubilities. The fungi presented tanninolitic activity when inoculated in samples of the crude effluent with supplement of nutrients, under aeration or not. The activity of the laccase of G. candidum in the same medium was higher in the 3rd day of the growth without aeration, occurring a reduction of that in the 5th day. On the other hand, the fungus P. chrysosporium presented a higher activity of laccase in the 7th day of the growth, also without aeration. Both fungi did not interfere in the color, turbidity, concentration of nitrates and nitrites of this medium. G.candidum revealed equal efficiency in the reduction of the concentration of phosphates of the crude effluent, under aeration (78.18%) and not aeration (79.33%) conditions. However, it did not reduce the COD. P. chrysosporium was efficient in the reduction of this COD, and the difference between the aerated growth (26.77%) and the not aerated one (29.55%) was very small. It did not reduce the total tanning bark concentration, but it diminished the concentration of phosphates under aerated (55.55%) and under not aerated (61.65%) condition. The addition of nutrients in the medium of diluted effluent (2 X, 4 X and 8 X) showed that there is a direct effect of the concentration of the COD on its percentage of removal by the inoculated fungi. There is also a direct effect on the remotion of total phenolic compounds and reduced glycids. The conversion of COD in the diluted effluent (8X) was higher in the growth of P. chrysosporium (65.66%) than in the one of G.candidum (57%). The same it can be said regarding to the best rates of phenol degradation (59.66% and 50.33%, respectively). The pH measured in the media supplemented with nutrients was always higher (7,56-7,8) than the initial one (5,5). In the higher dilution of the effluent (8X) plus the supplement of nutrients, the maximum removal of COD and total phenols after the treatment occurred in 7th day of incubation of both fungi. In all the cases of diluted samples plus supplement of nutrients, the discoloration drastically increased after the inoculation of the fungi. Therefore, the use of these microorganisms in the bioremediation of the effluent of sugar-alcohol industry is recommended only after a correction of the ratio C: N: P to about 100:1,6:1.