NON-TOLUENE-ASSOCIATED RESPIRATION IN A PSEUDOMONAS-PUTIDA 54G BIOFILM GROWN ON TOLUENE IN A FLAT-PLATE VAPOR-PHASE BIOREACTOR

Non-toluene-associated respiration (NTAR) within a Pseudomonas putida 54G biofilm growing on toluene as sole external carbon source was eval uated using oxygen microelectrodes in a flat-plate vapor-phase biologi cal reactor. Two fluorescent probes, 2,4-diamidino-2-phenylindole and 5-cyano-2,3-ditolyltetrazolium chloride, were used to evaluate the num ber of total and respiring cells respectively within the biofilm. Biof ilm samples were also analyzed for viable and toluene-culturable cells by spread-plating on non-selective and selective media respectively. Fractions of viable stressed, respiring and non-respiring cells within the biofilm were evaluated. The NTAR rate was positively correlated w ith the fraction of viable stressed and non-respiring cells within the biofilm, which suggested the capability of some cells to grow at the expense of leakage and lysis products coming from injured and dead cel ls. This effect was more pronounced at higher toluene concentration. R esults suggest that NTAR should be incorporated into mathematical mode ls of biofilm reactors degrading volatile organic carbon compounds.