Nitrate-dependent salicylate degradation by Pseudomonas butanovora under anaerobic conditions.

Nitrate-dependent salicylate degradation by the denitrifying Pseudomonas butanovora was investigated and the molar ratio of the cometabolism under anaerobic circumstances was determined. The bacterium was able to utilize salicylate as an electron donor for the reduction of nitrate. Salicylate was eliminated via catechol, which is degraded by means of catechol 2,3-oxygenases (meta-cleavage), forming 2-hydroxymuconic semialdehyde. The molar ratios of NO(3)(-)-N:salicylate existing during the experiment accorded well with the assumed 1:1 molar ratio. The tolerances of the growth, the salicylate degradation and the denitrification of P. butanovora to various heavy metal ions were also studied. Although the strain was tolerant to Pb(2+) and Cu(2+) up to 1 mM in complete medium, salicylate utilization took place only up to a concentration of 0.1 mM for both heavy metal ions. Of the heavy metal ions investigated, Cd(2+) (at a concentration of 0.05 mM) displayed the highest inhibitory effect on salicylate degradation by P. butanovora.

Investigation of the denitrification activity of immobilized Pseudomonas butanovora cells in the presence of different organic substrates.

An investigation was made of the effects of variation of the hydraulic retention time (HRT) and the concentrations of three different carbon sources (succinic acid, ethanol and acetic acid) on the denitrification activity of immobilized Pseudomonas butanovora cells. The highest denitrification activity was in all cases measured at a C: N ratio of 6: and a relatively low HRT (2.5 h). The highest denitrification rates were 1.17 kg NO3--N m(-3) d(-1) for succinic acid, 1.63 kg NO3--Nm(-3) d(-1) for ethanol and 1.53kg NO3--Nm(-3) d(-1) for acetic acid. At the same C:N ratios, ethanol and acetic acid proved to be better substrates for the reduction of nitrate and nitrite. The determined optimum C: N ratios were 1.78 +/- 0.31, 0.95 +/- 0.17, 1.76 +/- 0.42 for succinic acid, ethanol and acetic acid, respectively. The optimum C:N ratios for the different substrates did not change in response to an increased flow rate. At a C: N ratio of 3:1 and a HRT of 1.5 h, the immobilized cells did not retain their activity. Apart from the difference in the effectivity between the electron donors, the main influence on the denitrification rate was exerted by the flow rate The results of this study demonstrated that Pseudomonas butanovora can utilize all three of these carbon sources to achieve a high rate of denitrification.

Biological denitrification in a continuous-flow pilot bioreactor containing immobilized Pseudomonas butanovora cells.

Pseudomonas butanovora, a novel denitrifying bacterium, was immobilized in composite beads and filled into a reactor system. The pilot bioreactor average denitrification activity was at ethanol-C:nitrate-N ratios of 3:1 and 1.5:1 0.88 and 0.54 kg NO3(-)-Nm(-3) d(-1), respectively. The denitrification was stable in spite of the relatively low hydraulic retention times of 2.47 and 3 h. The nitrate content of the influent was almost completely reduced at the first level of the bioreactor and the nitrite formed underwent reduction in the upper part of the reactor. The experimentally determined optimum ethanol-C:nitrate-N ratio was 1.41 +/- 0.41. In consequence of the aerobic conditions, the acetic acid produced by the oxygenation of ethanol was also detectable in the reactor effluent. The pH of the effluent (7.58) never exceeded the acceptable maximum (8.5). The nitrate removal efficiency of the cells was nearly 1000% at both C:N ratios, and the nitrite content of the effluent was around the prescribed limit throughout the continuous operation. This continuous-flow pilot bioreactor containing immobilized P. butanovora cells proved an efficient denitrification system with a relatively low retention time.

The effects of NaCl and some heavy metals on the denitrification activity of Ochrobactrum anthropi.

Ochrobactrum anthropi is a well-known Gram-negative bacterium, with the ability to degrade atrazine, urea-formaldehyde and chlorophenols. Investigation were made of the nitrate and nitrite reduction capacities of the strain in succinate and glucose media, and the tolerance of its denitrification to NaCl and some heavy metals. Succinate proved to be a better carbon source to drive denitrification by O. anthropi. Batch fermentation studies in anaerobic succinate medium indicated reduction capacities of 85.4 +/- 9.1 and 48.6 +/- 5.2 mgh(-1)g(-1) dry cell for NO(3) (-) and NO(2) (-), respectively. The nitrite accumulation of the cells revealed that O. anthropi is a group C denitrifying bacterium. Its growth in DSM 1 broth containing NaCl up to 40 g l(-1) demonstrates that O. anthropi belongs in the group of moderately halophilic bacteria. Despite the fact that 42.5 g NaCl l(-1) caused 50% growth inhibition in DSM 1 broth, the cells in the stationary phase readily tolerated NaCl concentrations up to 100 g l(-1). Complete denitrification was achieved in test media containing 30 g NaCl l(-1) after 1 week and the nitrate reductase retained its activity up to 100 g NaCl l(-1). The cells were tolerant to Hg, Zn, Pb, Cu and Ni, and N(2) was producted at tolerated concentrations of the metal in the cases of Hg and Pb.