Summary: B urkholderia fungorum FLU 100 simultaneously oxidized any mixture of toluene, benzene and mono‐halogen benzenes to (3‐substituted) catechols with a selectivity of nearly 100%. Further metabolism occurred via enzymes of ortho cleavage pathways with complete mineralization. During the transformation of 3‐methylcatechol, 4‐carboxymethyl‐2‐methylbut‐2‐en‐4‐olide (2‐methyl‐2‐enelactone, 2‐ ML ) accumulated transiently, being further mineralized only after a lag phase of 2 h in case of cells pre‐grown on benzene or mono‐halogen benzenes. No lag phase, however, occurred after growth on toluene. Cultures inhibited by chloramphenicol after growth on benzene or mono‐halogen benzenes were unable to metabolize 2‐ ML supplied externally, even after prolonged incubation. A control culture grown with toluene did not show any lag phase and used 2‐ ML as a substrate. This means that 2‐ ML is an intermediate of toluene degradation and converted by specific enzymes. The conversion of 4‐methylcatechol as a very minor by‐product of toluene degradation in strain FLU 100 resulted in the accumulation of 4‐carboxymethyl‐4‐methylbut‐2‐en‐4‐olide (4‐methyl‐2‐enelactone, 4‐ ML ) as a dead‐end product, excluding its nature as a possible intermediate. Thus, 3‐methylcyclohexa‐3,5‐diene‐1,2‐diol, 3‐methylcatechol, 2‐methyl muconate and 2‐ ML were identified as central intermediates of productive ortho cleavage pathways for toluene metabolism in B . fungorum FLU 100.

The dibenzofuran-degrading bacterial strain DPO360 represents a new species of the genus Terrabacter together with the previously described dibenzofuran-mineralizing bacterial strain DPO1361 (K.-H. Engesser, V. Strubel, K. Christoglou, P. Fischer, and H. G. Rast, FEMS Microbiol. Lett. 65:205-210, 1989; V. Strubel, Ph.D. thesis, University of Stuttgart, Stuttgart, Germany, 1991; V. Strubel, H. G. Rast, W. Fietz, H.-J. Knackmuss, and K.-H. Engesser, FEMS Microbiol. Lett. 58:233-238, 1989). Two 2,3-dihydroxybiphenyl-1,2-dioxygenases (BphC1 and BphC2) and one catechol-2,3-dioxygenase (C23O) were shown to be expressed in Terrabacter sp. strain DPO360 growing with dibenzofuran as a sole source of carbon and energy. These enzymes exhibited strong sensitivity to oxygen. They were purified to apparent homogeneity as homodimers (BphC and BphC2) and as a homotetrameric catechol-2,3-dioxygenase (C23O). According to their specificity constants kcat/Km, both BphC1 and BphC2 were shown to be responsible for the cleavage of 2,2',3-trihydroxybiphenyl, the first metabolite in dibenzofuran mineralization along the angular dioxygenation pathway. With this substrate, BphC2 exhibited a considerably higher kcat/Km, value (183 microM/min) than BphC1 (29 microM/min). Catechol-2,3-dioxygenase was recognized to be not involved in the ring cleavage of 2,2',3-trihydroxybiphenyl (kcat/Km, 1 microM/min). Analysis of deduced amino acid sequence data of bphC1 revealed 36% sequence identity to nahC from Pseudomonas putida PpG7 (S. Harayama and M. Rekik, J. Biol. Chem. 264:15328-15333, 1989) and about 40% sequence identity to various bphC genes from different Pseudomonas and Rhodococcus strains. In addition, another 2,3-dihydroxybiphenyl-1,2-dioxygenase gene (bphC3) was cloned from the genome of Terrabacter sp. strain DPO360. Expression of this gene, however, could not be detected in Terrabacter sp. strain DPO360 after growth with dibenzofuran.

Twenty strains isolated from sewage sludge were found to degrade various ethers, including alkyl ethers, aralkyl ethers, and dibenzyl ether. In Rhodococcus strain DEE5151, induction of ether degradation needed substrates exhibiting at least one unsubstituted Cα-methylene moiety as the main structural prerequisite. The cleavage reaction observed with anisole, phenetole, and dibenzyl ether indicates that the initial oxidation occurs at such respective Cα positions. Diethyl ether-induced strain DEE5151 degraded dibenzyl ether via intermediately accumulated benzoic acid. Phenetole seems to be subject also to another ether-cleaving enzyme. Other strains of this group showed different enzymatic activities towards the substrate classes investigated.

A combined system of a biotrickling filter and a non-thermal plasma (NTP) in a downstream airflow was operated for 1220 days for treatment of emissions of styrene and secondary emissions of germs formed in the biological process. The biotrickling filter was operated at variable inlet concentrations, empty bed residence times (EBRT), type and dosage of fertilizers, irrigation densities, and starvation periods, while dielectric barrier discharge and corona discharge were operated at different specific input energy levels to achieve optimal conditions. Under these conditions, efficiencies in the removal of volatile organic compounds (VOCs), germs and styrene of 96–98%, 1–4 log units and 24.7–50.1 g C m⁻³ h⁻¹ were achieved, respectively. Fluid simulations of the NTP and a germ emission-based clocking of the discharge reveal further energy saving potentials of more than 90%. The aim of an energy-efficient elimination of VOCs through a biotrickling filter and of secondary germ emissions by a NTP stage in a downstream airflow for potential re-use of purified waste gas as process gas for industrial application was successfully accomplished.