Response of ligninolytic macrofungi to the herbicide atrazine: dose-response bioassays

Biodegradation of atrazine and ligninolytic enzyme production by basidiomycete strains

BACKGROUND

Atrazine is one of the most widespread chlorinated herbicides, leaving large bulks in soils and groundwater. The biodegradation of atrazine by bacteria is well described, but many aspects of the fungal metabolism of this compound remain unclear. Thus, we investigated the toxicity and degradation of atrazine by 13 rainforest basidiomycete strains.

RESULTS

In liquid medium, Pluteus cubensis SXS320, Gloelophyllum striatum MCA7, and Agaricales MCA17 removed 30, 37, and 38%, respectively, of initial 25 mg L- 1 of the herbicide within 20 days. Deficiency of nitrogen drove atrazine degradation by Pluteus cubensis SXS320; this strain removed 30% of atrazine within 20 days in a culture medium with 2.5 mM of N, raising three metabolites; in a medium with 25 mM of N, only 21% of initial atrazine were removed after 40 days, and two metabolites appeared in culture extracts. This is the first report of such different outcomes linked to nitrogen availability during the biodegradation of atrazine by basidiomycetes. The herbicide also induced synthesis and secretion of extracellular laccases by Datronia caperata MCA5, Pycnoporus sanguineus MCA16, and Polyporus tenuiculus MCA11. Laccase levels produced by of P. tenuiculus MCA11 were 13.3-fold superior in the contaminated medium than in control; the possible role of this enzyme on atrazine biodegradation was evaluated, considering the strong induction and the removal of 13.9% of the herbicide in vivo. Although 88% of initial laccase activity remained after 6 h, no evidence of in vitro degradation was observed, even though ABTS was present as mediator.

CONCLUSIONS

This study revealed a high potential for atrazine biodegradation among tropical basidiomycete strains. Further investigations, focusing on less explored ligninolytic enzymes and cell-bound mechanisms, could enlighten key aspects of the atrazine fungal metabolism and the role of the nitrogen in the process.

Ligninolytic behavior of the white-rot fungus Stereum ostrea under influence of culture conditions, inducers and chlorpyrifos

The production of three ligninolytic enzymes, laccase (LAC), manganese peroxidase (MnP) and lignin peroxidase (LiP) by the white-rot fungus, Stereum ostrea, was significantly more in Koroljova liquid medium in the presence of chlorpyrifos under shaking conditions than under stationary conditions. These enzymes were secreted into the broth to the extent of 214.37, 82.75 and 8.05 U/ml under influence of chlorpyrifos on 10th day of incubation in comparison with 138.06, 51.85 and 6.44 U/ml, respectively, under similar conditions in control. Maximum production of LAC, MnP and LiP on liquid medium with/without chlorpyrifos under stationary conditions did not exceed 80-85, 33-40, 0.6-0.7 U/ml, respectively. Among lignosulfonic acid, veratryl alcohol (VA), gallic acid (GA) and tannic acid tested, GA induced maximum production of LAC (300.53 U/ml) and MnP (181.66 U/ml) after 10 days of growth in the presence of chlorpyriphos, while maximum LiP (1.134 U/ml) was produced when grown with the inducer VA during this period. Our data suggest that chlorpyrifos and inducers interacted positively in producing higher amounts of the ligninolytic enzymes in S. ostrea.

Biodegradation of NSAIDs and their effect on the activity of ligninolytic enzymes from Pleurotus djamor

In this work, the white-rot fungus Pleurotus djamor was used for the first time to determine the degradation kinetics of the nonsteroidal anti-inflammatory drugs diclofenac, naproxen and, ketoprofen, either individually or in mixtures, in submerged cultures. Removal of 93% individual diclofenac and 99% diclofenac in mixtures with naproxen and ketoprofen at 6 h of incubation with the fungus was achieved. The elimination levels of naproxen and ketoprofen individually were 90% and 87%, respectively, after 48 h of incubation. However, the removal levels of these compounds in mixtures were 85% and 83%, respectively. On the other hand, during the degradation kinetics analysis, the enzymatic activities of laccases, manganese peroxidases, and lignin peroxidases were evaluated, yielding values of 3700, 270 and 31 U/L, respectively. Additionally, it was demonstrated that during degradation of diclofenac or the three drugs mixed in the submerged cultures, the enzymatic activity of extracellular laccases expressed by P. djamor increased by 200% and 300%, respectively. The activity of manganese peroxides increased by 126% with diclofenac and 138% when the mixture of drugs was added to the cultures. On the other hand, lignin peroxidase only increased activity by 123% with the drug mixture.

Cold-stress response during the stationary-growth phase of Antarctic and temperate-climate Penicillium strains

Cold-induced oxidative stress during the aging of three Penicillium strains (two Antarctic and one from a temperate region) in stationary culture was documented and demonstrated a significant increase in the protein carbonyl content, the accumulation of glycogen and trehalose, and an increase in the activities of antioxidant enzymes (superoxide dismutase and catalase). The cell response to a temperature downshift depends on the degree of stress and the temperature characteristics of the strains. Our data give further support for the role of oxidative stress in the aging of fungi in stationary cultures. Comparing the present results for the stationary growth phase with our previous results for the exponential growth phase was informative concerning the relationship between the cold-stress response and age-related changes in the tested strains. Unlike the young cells, stationary-phase cultures demonstrated a more pronounced level of oxidative damage, as well as decreased antioxidant defence.