Manganese promoted wheat straw decomposition by regulating microbial communities and enzyme activities

AIMS

This study investigated the dose-effect of manganese (Mn) addition on wheat straw (WS) decomposition, and explored the potential mechanisms of Mn involved in the acceleration of WS decomposition in regards to the soil microbial communities and enzyme activities.

METHODS AND RESULTS

A 180-day incubation experiment was performed to examine the decomposition of WS under four Mn levels, that is, 0, 0.25, 1 and 2 mg g^-1 . The effects of microbial communities and enzyme activities were evaluated using control (0 mg g^-1 ) and Mn (0.25 mg g^-1 ) treatments. Our results revealed that Mn (0.25 mg g^-1 ) addition significantly increased WS decomposition, and enhanced the release of carbon and nitrogen. Optimal Mn addition (0.25 mg g^-1 ) also caused significant increases in the activity of neutral xylanase (NEX), laccase (Lac), manganese peroxidase (MnP) and lignin peroxidase (LiP) within the incubation period. Mn (0.25 mg g^-1 ) addition also enriched some operational taxonomic units (OTUs) that, in turn, had the potential ability to decompose crop straw, such as secreting lignocellulolytic enzymes.

CONCLUSIONS

Mn (0.25 mg g^-1 ) could promote WS decomposition through enrichment of the microbial species involved in biomass decomposition, which enhanced the lignocellulose-degrading enzyme activity.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study provides evidence for Mn to promote WS biodegradation after Mn application, opening new windows to improve the utilization efficiency of crop residues.

Enzymatic decolorization of melanin by lignin peroxidase from Phanerochaete chrysosporium

Skin darkening results as a consequence of the accumulation of skin pigment melanin. To combat this, the amplitude of skin lightening agents are commercially available, most of which inhibit melanin synthesis. Decolorization of melanin is an alternative method of skin lightening. In this study, we show that lignin peroxidase (LiP), an extracellular enzyme purified from Phanerochaete chrysosporium NK-1 isolated from a forest soil can effectively degrade and decolorize melanin in vitro. Decolorization conditions including pH, temperature, incubation time, enzyme concentration, and mediator addition were investigated to optimize the reaction conditions. The results indicate that pH 3, 40 °C, 15 IU/ml, and 10 h incubation were the optimal conditions for the decolorization of the melanin. The use of the mediator, veratryl alcohol was also found effective to enhance the efficacy of the melanin decolonization, with up to 92% decolorization. The scanning electron microscopy results showed void spaces on the treated melanin granules as compared to the untreated sample, indicating the degradation of melanin. Changes in the fingerprint region of the melanin were observed. Between wavenumbers 1500–500 cm⁻¹, for example, the presence of new peaks in the treated melanin at 1513, 1464, and 1139 cm⁻¹ CH₂, CH₃ bend and C–O–C stretch represented structural changes. A new peak at 2144 cm⁻¹ (alkynyl C≡C stretch) was also detected in the decolorized melanin. The cytotoxicity study has shown that the treated melanin and LiP have low cytotoxic effects; however, the mediator of veratryl alcohol could result in high mortality which suggests that its use should be meticulously tested in formulating health and skincare products. The findings of the study suggest that LiP produced by Phanerochaete chrysosporium has the potential to be used in the medical and cosmetic industries, particularly for the development of biobased cosmetic whitening agents.

Soil labile organic carbon fractions and soil enzyme activities after 10 years of continuous fertilization and wheat residue incorporation

Labile organic carbon (LOC) fractions and related enzyme activities in soils are considered to be early and sensitive indicators of soil quality changes. We investigated the influences of fertilization and residue incorporation on LOC fractions, enzyme activities, and the carbon pool management index (CPMI) in a 10-year field experiment. The experiment was composed of three treatments: (1) no fertilization (control), (2) chemical fertilizer application alone (F), and (3) chemical fertilizer application combined with incorporation of wheat straw residues (F + R). Generally, the F + R treatment led to the highest concentrations of the LOC fractions. Compared to the control treatment, the F + R treatment markedly enhanced potential activities of cellulase (CL), β-glucosidase (BG), lignin peroxidase (LiP), and manganese peroxidase (MnP), but decreased laccase (LA) potential activity. Partial least squares regression analysis suggested that BG and MnP activities had a positive impact on the light-fraction organic carbon (LFOC), permanganate-oxidizable carbon (POXC), and dissolved organic carbon (DOC) fractions, whereas laccase activity had a negative correlation with those fractions. In addition, the F + R treatment significantly increased the CPMI compared to the F and control treatments. These results indicated that combining fertilization with crop residues stimulates production of LOC and could be a useful approach for maintaining sustainable production capacity in lime concretion black soils along the Huai River region of China.

Lignin peroxidase isoenzyme: a novel approach to biodegrade the toxic synthetic polymer waste

Fungal metabolites are playing an immense role in developing various sustainable waste treatment processes. The present study aimed at production and characterization of fungal lignin peroxidase (EC 1.11.1.14) with a potential to degrade Polyvinyl Chloride. Optimization studies revealed that the maximum enzyme production occurred at a temperature 25°C, pH 5 in the 4th week of the incubation period with fungal strain. Enzyme assay was performed to find out the dominating enzyme in the culture broth. The molecular weight of the enzyme was found to be 46 kDa. Partially purified lignin peroxidase from Phanerocheate chrysosporium was used for the degradation of PVC films. A significant reduction in the weight of PVC film was observed (31%) in shake flask experiment. FTIR spectra of the enzyme-treated plastic film revealed structural changes in the chemical composition, indicating a specific peak at 2943 cm^-1 that corresponded to alkenyl C-H stretch. Moreover, deterioration on the surface of PVC films was confirmed by Scanning Electron Microscopy tracked through activity assay for the lignin peroxidase. Extracellular lignin peroxidases from P. chrysosporium play a significant role in the degradation of complex polymeric compounds like PVC.

Carotene-degrading activities from Bjerkandera adusta possess an application in detergent industries

Four extracellular enzymes, a versatile peroxidase, a manganese peroxidase, a dye-decolorizing peroxidase and a lignin peroxidase were discovered in liquid cultures of the basidiomycete Bjerkandera adusta. All of them cleaved β-carotene effectively. Expression was enhanced in the presence of β-carotene or Coomassie Brilliant Blue and peaked after 7-9 days. The monomeric proteins were purified by ion exchange and size exclusion chromatography and exhibited molecular masses of 41, 43, 51 and 43 kDa, respectively. The coding sequences showed homologies from 61 to 89 % to peroxidases from other basidiomycetes. The novel enzymes retained strong activity even in the absence of hydrogen peroxide and at alkaline pH. De-staining of fabrics using detergent-tolerant enzymes may help to save the most important bio-resources, energy and water, in washing processes and led to green processes in textile cleaning.

Fungal colonization and enzyme-mediated metabolism of waste coal by Neosartorya fischeri strain ECCN 84

Colonization and oxidative metabolism of South African low-rank discard coal by the fungal strain ECCN 84 previously isolated from a coal environment and identified as Neosartorya fischeri was investigated. Results show that waste coal supported fungal growth. Colonization of waste coal particles by N. fischeri ECCN 84 was associated with the formation of compact spherical pellets or sclerotia-like structures. Dissection of the pellets from liquid cultures revealed a nucleus of "engulfed" coal which when analyzed by energy dispersive X-ray spectroscopy showed a time-dependent decline in weight percentage of elemental carbon and an increase in elemental oxygen. Proliferation of peroxisomes in hyphae attached to coal particles and increased extracellular laccase activity occurred after addition of waste coal to cultures of N. fischeri ECCN 84. These results support a role for oxidative enzyme action in the biodegradation of coal and suggest that extracellular laccase is a key component in this process.