Search

White rot fungi can oxidize high-molecular-weight polycyclic aromatic hydrocarbons (PAH) rapidly to polar metabolites, but only limited mineralization takes place. The objectives of this study were to determine if the polar metabolites can be readily mineralized by indigenous microflora from several inoculum sources, such as activated sludge, forest soils, and PAH-adapted sediment sludge, and to determine if such metabolites have decreased mutagenicity compared to the mutagenicity of the parent PAH. 14C-radiolabeled benzo[a]pyrene was subjected to oxidation by the white rot fungus Bjerkandera sp. strain BOS55. After 15 days, up to 8.5% of the [14C]benzo[a]pyrene was recovered as 14CO2 in fungal cultures, up to 73% was recovered as water-soluble metabolites, and only 4% remained soluble in dibutyl ether. Thin-layer chromatography analysis revealed that many polar fluorescent metabolites accumulated. Addition of indigenous microflora to fungal cultures with oxidized benzo[a]pyrene on day 15 resulted in an initially rapid increase in the level of 14CO2 recovery to a maximal value of 34% by the end of the experiments (>150 days), and the level of water-soluble label decreased to 16% of the initial level. In fungal cultures not inoculated with microflora, the level of 14CO2 recovery increased to 13.5%, while the level of recovery of water-soluble metabolites remained as high as 61%. No large differences in 14CO2 production were observed with several inocula, showing that some polar metabolites of fungal benzo[a]pyrene oxidation were readily degraded by indigenous microorganisms, while other metabolites were not. Of the inocula tested, only PAH-adapted sediment sludge was capable of directly mineralizing intact benzo[a]pyrene, albeit at a lower rate and to a lesser extent than the mineralization observed after combined treatment with white rot fungi and indigenous microflora. Fungal oxidation of benzo[a]pyrene resulted in rapid and almost complete elimination of its high mutagenic potential, as observed in the Salmonella typhimurium revertant test performed with strains TA100 and TA98. Moreover, no direct mutagenic metabolite could be detected during fungal oxidation. The remaining weak mutagenic activity of fungal cultures containing benzo[a]pyrene metabolites towards strain TA98 was further decreased by subsequent incubations with indigenous microflora.

By using styrene as the sole source of carbon and energy in concentrations of 10 to 500 microM, 14 strains of aerobic bacteria and two strains of fungi were isolated from various soil and water samples. In cell extracts of 11 of the bacterial isolates, a novel flavin adenine dinucleotide-requiring styrene monooxygenase activity that oxidized styrene to styrene oxide (phenyl oxirane) was detected. In one bacterial strain (S5), styrene metabolism was studied in more detail. In addition to styrene monooxygenase, cell extracts from strain S5 contained styrene oxide isomerase and phenylacetaldehyde dehydrogenase activities. A pathway for styrene degradation via styrene oxide and phenylacetaldehyde to phenylacetic acid is proposed.

Aromatic compounds of both natural and man-made sources abound in the environment. The degradation of such chemicals is mainly accomplished by microorganisms. This review provides key background information but centres on recent developments in the bacterial degradation of selected man-made aromatic compounds. An aromatic compound can only be considered to be biodegraded if the ring undergoes cleavage, and this is taken as the major criteria for inclusion in this review (although the exact nature of the enzymic ring-cleavage has not been confirmed in all cases discussed). The biodegradation of benzene, certain arenes, biphenyl and selected fused aromatic hydrocarbons, by single bacterial isolates, are dealt with in detail.

The exposure of bacterial cells to pulsed electric fields (PEF) leads to the reversible formation of pores in the cell membrane if an applied energy is below the critical level. Therefore, the effect of electric field pulses with amplitudes below 14 kV/cm and the applied energy up to 12.2 J/cm³ on the growth of Lactobacillus plantarum 564 cells was investigated. After PEF treatments, the growth of lactobacilli in De Man-Rogosa-Sharpe broth at 37 °C was monitored by isothermal calorimetry, absorbance and plate counts. All the applied treatments resulted in a higher growth rate of PEF-treated cells during early and mid-log phase, especially bacterial samples treated with lower field intensities (1.3-5.5 J/cm³). The transport of ions and molecules through the cell membrane (which facilitates the growth of electroporated lactobacilli) was particularly evident in the mid-exponential growth phase, where the doubling time was reduced more than 3 times after the exposure to electric pulses of 5.5 J/cm³. The heat production rate during the growth of electroporated cells was also higher, indicating the enhanced metabolic activity of PEF-treated cells. Moreover, the electroporated cells had a better acidification ability than the untreated ones. It can be summarized that the applied PEF treatments with an energy input of below 12 J/cm³ potentially induce reversible electroporation of the cell membrane, which has a positive impact on the growth and metabolic activity of the cells of lactobacilli. [ABSTRACT FROM AUTHOR]

The degradation of alkanes and alcohols by Rhodococcus erythropolis DCL14 growing cells was tested at different reactor scales, ranging from a 2-L fermenter to 300 μL 96-well plates. The highest growth rates were attained in the fermenter, where pH, temperature and aeration rate, in particular, are monitored and controlled. However, the results acquired in reactors smaller than 100 mL indicate that these reactors may be successfully used in testing carbon sources, since the normalized results obtained with the different carbons sources were maintained in the 100-0.3 mL range. This study also shows the great potential of R. erythropolis DCL14 cells to degrade a wide range of alcohols and alkanes, which may be used in bioremediation of contaminated sites. [ABSTRACT FROM AUTHOR]

The behaviour of cells of Rhodococcus erythropolis DCL14, Xanthobacter Py2, Arthrobacter simplex and Mycobacterium sp. NRRL B-3805, in biphasic systems containing different organic solvents was evaluated and compared. The data, obtained mainly by fluorescence microscopy and image analysis, was interpreted using principal components analysis (PCA). With this technique, the variability of the data could be summarised in 7 components, representing 75.8% of the variance of the data. Over a third of the variance could be explained by the first two principal components which represent solvent toxicity. Apparently this is the major factor influencing cell behaviour in an organic:aqueous system. However, factors such as substrate concentration, cell adaptation ability (resulting in morphological changes and aggregation or separation of cells) and membrane composition (specific to each strain) also play an important role in cell resistance to solvent toxicity. The results regarding cell shape indicate that loss of viability occurs, in the tested bacterial strains, after incorporation of molecules of solvent in the cellular membrane. This should result in an increase in membrane fluidity, and thus, in an alteration of cell shape. The ability to form "self-defence" clusters was observed to be different amongst the four strains. X. Py2 showed, in general, a low tendency to form aggregates under the tested conditions; A. simplex and R. erythropolis aggregated mainly in the presence of low log P solvents; and Mycobacterium. sp. cells showed a high ability to aggregate. [ABSTRACT FROM AUTHOR]

The solvent-tolerant bacterium Pseudomonas putida S12, which adapts its membrane lipids to the presence of toxic solvents by a cis to trans isomerization of unsaturated fatty acids, was used to study possible in vivo regiospecificity of the isomerase. Cells were supplemented with linoleic acid (C18:2Δ9-cis,Δ12-cis), a fatty acid that cannot be synthesized by this bacterium, but which was incorporated into membrane lipids up to an amount of 15% of total fatty acids. After addition of 1-octanol, which was used as an activator of the cis-trans isomerase, the linoleic acid was converted into the Δ9-trans,Δ12-cis isomer, while the Δ9-cis,Δ12-trans and Δ9-trans,Δ12-trans isomers were not synthesized. Thus, for the first time, regiospecific in vivo formation of novel, mixed cis/trans isomers of dienoic fatty acid chains was observed. The maximal conversion (27–36% of the chains) was obtained at 0.03–0.04% (v/v) octanol, after 2 h. The observed regiospecificity of the enzyme, which is located in the periplasmic space, could be due to penetration of the enzyme to a specific depth in the membrane as well as to specific molecular recognition of the substrate molecules. [ABSTRACT FROM AUTHOR]

Twenty-one microorganisms were screened for their ability to convert nitroaromatics into 3-nitrocatechol as a result of the action of an oxygenase. Cultures containing toluene dioxygenases and phenol monooxygenases accumulated 3-nitrocatechol during incubation with nitrobenzene and nitrophenol, respectively. Nocardia S3 was selected and studied in more detail. Toluene-pregrown cultures were able to degrade nitrobenzene with a concomitant formation of 3-nitrocatechol. The rates of nitrobenzene utilization decreased throughout the biotransformation period and finally the accumulation ceased. The gradual deterioration of the biotransformation rates was not a consequence of depletion of the NADH pool, but was due to the accumulation of 3-nitrocatechol. The inhibition of nitrobenzene biotransformation by 3-nitrocatechol greatly impacts 3-nitrocatechol production processes . [ABSTRACT FROM AUTHOR]

The aim of the study was to investigate whether toxic fine chemical production can be improved using the solvent-tolerant Pseudomonas putida S12 in a two-liquid-phase system consisting of aqueous media and a water-immiscible octanol phase with production of 3-methylcatechol from toluene as the model conversion. For this purpose the genes involved in this conversion, todC1C2BAD from P. putida F1, were introduced into P. putida S12 with high stable expression. Production of 3-methylcatechol was monitored in batch incubations with different media using a single medium and a two-liquid medium–octanol system. The maximum concentration of 3-methylcatechol increased two-fold using the two-liquid medium–octanol system, irrespective of the selected medium. [ABSTRACT FROM AUTHOR]