• Energy Research

Aim of this work was to investigate the ability of Lentinus (Panus) tigrinus to degrade and detoxify a chlorobenzoate (CBA) mixture composed of mono-, di- and tri-chlorinated isomers. The degradation process was investigated as a function of both the growing medium (i.e. low N Kirk's and malt extract-glucose medium) and cultivation conditions (i.e. stationary and shaken cultures). The majority of CBAs were quantitatively degraded within the early 15 d from spiking with the notable exception of the double ortho-chlorinated compounds, 2,6-di-, 2,3,6-tri- and 2,4,6-tri-CBA. Analysis of the degradation intermediates indicated the occurrence of side chain reduction, hydroxylation and methylation reactions. Although CBAs stimulated laccase production, in vitro experiments with a purified L. tigrinus laccase isoenzyme demonstrated its inability to participate in the initial attack on CBAs even in the presence of redox mediators; similar results were found with a Mn-peroxidase isoenzyme. Conversely, prompt degradation was observed upon 1h incubation of CBAs with a purified microsomal fraction containing cytochrome P-450 monooxygenase. The nature of some reaction products (i.e. hydroxylated derivatives), the dependency of the reaction on NADPH and its susceptibility to either CO or piperonyl butoxide inhibition confirmed the involvement of L. tigrinus cytochrome P-450 in the early steps of CBA degradation.

Aim of this work was to investigate the ability of Lentinus (Panus) tigrinus to degrade and detoxify a chlorobenzoate (CBA) mixture composed of mono-, di- and tri-chlorinated isomers. The degradation process was investigated as a function of both the growing medium (i.e. low N Kirk's and malt extract-glucose medium) and cultivation conditions (i.e. stationary and shaken cultures). The majority of CBAs were quantitatively degraded within the early 15 d from spiking with the notable exception of the double ortho-chlorinated compounds, 2,6-di-, 2,3,6-tri- and 2,4,6-tri-CBA. Analysis of the degradation intermediates indicated the occurrence of side chain reduction, hydroxylation and methylation reactions. Although CBAs stimulated laccase production, in vitro experiments with a purified L. tigrinus laccase isoenzyme demonstrated its inability to participate in the initial attack on CBAs even in the presence of redox mediators; similar results were found with a Mn-peroxidase isoenzyme. Conversely, prompt degradation was observed upon 1h incubation of CBAs with a purified microsomal fraction containing cytochrome P-450 monooxygenase. The nature of some reaction products (i.e. hydroxylated derivatives), the dependency of the reaction on NADPH and its susceptibility to either CO or piperonyl butoxide inhibition confirmed the involvement of L. tigrinus cytochrome P-450 in the early steps of CBA degradation.

Objective of this study was to assess the single or combined effect of a plant oil and a lignocellulosic waste, namely soybean oil (SO) and maize stalks (MS), respectively, on resident microbiota and bioremediation performances of a soil historically contaminated by medium to highly chlorinated PCBs. Higher concentrations of both biphenyl- and chlorobenzoate-degrading cultivable bacteria were found in the MS-amended microcosms (MSM) than the non amended or SO-amended ones after 30 d incubation at 28°C. Fungal growth, instead, was strikingly stimulated in the microcosms that had undergone concomitant MS and SO supplementation (MS-SOM). Denaturing gradient gel electrophoresis analyses of 16S and 18S rRNA genes showed that both amendments promoted a remarkable increase in both bacterial and fungal biodiversity. The abundances of biphenyl-2,3-dioxygenase (bph) and that of catechol-2,3-dioxygenase (C230) genes in the non-amended contaminated soil were constant over time. Conversely, after 60 d incubation, bph and C230 abundances increased 2.8- and 61-fold in the MSM, respectively, and, in the MS-SOM, 1.4- and 46-fold, respectively, with respect to the zero time point. Although the overall PCB removal was not positively affected by the amendments, the concomitant presence of both MS and SO led to significantly higher depletions of hexa-, hepta-, octa- and nona-chlorinated congeners than in the non-amended microcosms (i.e. 24.6, 22, 20.5 and 9.5%, versus 19.4, 16.4, 14.7 and 6.1%, respectively). In all microcosms, PCB degradation was negatively correlated with hydrophobicity, organic matter/water partition coefficient, molecular weight and extent of chlorination of the pollutants with the notable exception of the MS-SOM ones where such a relationship was less stringent.

Objective of this study was to assess the single or combined effect of a plant oil and a lignocellulosic waste, namely soybean oil (SO) and maize stalks (MS), respectively, on resident microbiota and bioremediation performances of a soil historically contaminated by medium to highly chlorinated PCBs. Higher concentrations of both biphenyl- and chlorobenzoate-degrading cultivable bacteria were found in the MS-amended microcosms (MSM) than the non amended or SO-amended ones after 30 d incubation at 28°C. Fungal growth, instead, was strikingly stimulated in the microcosms that had undergone concomitant MS and SO supplementation (MS-SOM). Denaturing gradient gel electrophoresis analyses of 16S and 18S rRNA genes showed that both amendments promoted a remarkable increase in both bacterial and fungal biodiversity. The abundances of biphenyl-2,3-dioxygenase (bph) and that of catechol-2,3-dioxygenase (C230) genes in the non-amended contaminated soil were constant over time. Conversely, after 60 d incubation, bph and C230 abundances increased 2.8- and 61-fold in the MSM, respectively, and, in the MS-SOM, 1.4- and 46-fold, respectively, with respect to the zero time point. Although the overall PCB removal was not positively affected by the amendments, the concomitant presence of both MS and SO led to significantly higher depletions of hexa-, hepta-, octa- and nona-chlorinated congeners than in the non-amended microcosms (i.e. 24.6, 22, 20.5 and 9.5%, versus 19.4, 16.4, 14.7 and 6.1%, respectively). In all microcosms, PCB degradation was negatively correlated with hydrophobicity, organic matter/water partition coefficient, molecular weight and extent of chlorination of the pollutants with the notable exception of the MS-SOM ones where such a relationship was less stringent.

The ability of stationary and shaken Lentinus tigrinus CBS 577.79 liquid cultures to degrade a mixture of polycyclic aromatic hydrocarbons (PAHs) in N-rich (i.e., malt extract glucose, MEG) and in N-limited (low-N Kirk's medium, LNKM) media was investigated. Best results were obtained in shaken cultures where PAHs were degraded by 91% and 97% in MEG and LNKM, respectively; in stationary cultures, on the contrary, the degradation was never higher than 50%. Laccase activity was predominant on MEG while Mn-peroxidase (MnP) was preferentially produced in LNKM. The identification of degradation products showed the presence of several PAH derivatives, such as quinones, dicarboxylated and ring fission derivatives, presumably derived from the action of lignin-modifying enzymes. The presence of some degradation products (e.g., hydroxylated derivatives of anthrone and phenanthrene 9,10-dihydrodiol) suggested the possible involvement of cytochrome P-450-epoxide hydrolase system, the active form of which was found in 7-day-old cultures on MEG. In vitro experiments showed that the MnP from L. tigrinus had wider PAH substrate range and higher oxidation ability than the laccase produced by the same strain.

The ability of stationary and shaken Lentinus tigrinus CBS 577.79 liquid cultures to degrade a mixture of polycyclic aromatic hydrocarbons (PAHs) in N-rich (i.e., malt extract glucose, MEG) and in N-limited (low-N Kirk's medium, LNKM) media was investigated. Best results were obtained in shaken cultures where PAHs were degraded by 91% and 97% in MEG and LNKM, respectively; in stationary cultures, on the contrary, the degradation was never higher than 50%. Laccase activity was predominant on MEG while Mn-peroxidase (MnP) was preferentially produced in LNKM. The identification of degradation products showed the presence of several PAH derivatives, such as quinones, dicarboxylated and ring fission derivatives, presumably derived from the action of lignin-modifying enzymes. The presence of some degradation products (e.g., hydroxylated derivatives of anthrone and phenanthrene 9,10-dihydrodiol) suggested the possible involvement of cytochrome P-450-epoxide hydrolase system, the active form of which was found in 7-day-old cultures on MEG. In vitro experiments showed that the MnP from L. tigrinus had wider PAH substrate range and higher oxidation ability than the laccase produced by the same strain.