Bioremediation of high molecular weight polycyclic aromatic hydrocarbons: a review of the microbial degradation of benzo[a]pyrene.

Biological conversion of lignocellulosic biomass to ethanol

The use of higher plants to remediate contaminated land is known as phytoremediation, a term coined 15 years ago Among green technologies addressed to metal pollution, phytoextraction has received increasing attention starting from the discovery of hyperaccumulator plants, which are able to concentrate high levels of specific metals in the above-ground harvestable biomass The small shoot and root growth of these plants and the absence of their commercially available seeds have stimulated study on biomass species, including herbaceous field crops We review here the results of a bibliographical survey from 1995 to 2009 in CAB abstracts on phytoremediation and heavy metals for crop species, citations of which have greatly increased, especially after 2001 Apart from the most frequently cited Brassica juncea (L) Czern, which is often referred to as an hyperaccumulator of various metals, studies mainly focus on Helianthus annuus L, Zea mays L and Brassica napus L, the last also having the greatest annual increase in number of citations Field crops may compensate their low metal concentration by a greater biomass yield, but available data from in situ experiments are currently very few The use of amendments or chelators is often tested in the field to improve metal recovery, allowing above-normal concentrations to be reached Values for Zn exceeding 1,000 mg kg−1 are found in Brassica spp, Phaseolus vulgaris L and Zea mays, and Cu higher than 500 mg kg−1 in Zea mays, Phaseolus vulgaris and Sorghum bicolor (L) Moench Lead greater than 1,000 mg kg−1 is measured in Festuca spp and various Fabaceae Arsenic has values higher than 200 mg kg−1 in sorghum and soybean, whereas Cd concentrations are generally lower than 50 mg kg−1 Assisted phytoextraction is currently facilitated by the availability of low-toxic and highly degradable chelators, such as EDDS and nitrilotriacetate Currently, several experimental attempts are being made to improve plant growth and metal uptake, and results are being achieved from the application of organic acids, auxins, humic acids and mycorrhization The phytoremediation efficiency of field crops is rarely high, but their greater growth potential compared with hyperaccumulators should be considered positively, in that they can establish a dense green canopy in polluted soil, improving the landscape and reducing the mobility of pollutants through water, wind erosion and water percolation

Field crops for phytoremediation of metal-contaminated land. A review

The genus Pleurotus comprises a group of edible ligninolytic mushrooms with medicinal properties and important biotechnological and environmental applications. The cultivation of Pleurotus spp is an economically important food industry worldwide which has expanded in the past few years. P. ostreatus is the third most important cultivated mushroom for food purposes. Nutritionally, it has unique flavor and aromatic properties; and it is considered to be rich in protein, fiber, carbohydrates, vitamins and minerals. Pleurotus spp are promising as medicinal mushrooms, exhibiting hematological, antiviral, antitumor, antibiotic, antibacterial, hypocholesterolic and immunomodulation activities. The bioactive molecules isolated from the different fungi are polysaccharides. One of the most important aspects of Pleurotus spp is related to the use of their ligninolytic system for a variety of applications, such as the bioconversion of agricultural wastes into valuable products for animal feed and other food products and the use of their ligninolytic enzymes for the biodegradation of organopollutants, xenobiotics and industrial contaminants. In this Mini-Review, we describe the properties of Pleurotus spp in relation to their biotechnological applications and potential.

Biotechnological applications and potential of wood-degrading mushrooms of the genus Pleurotus.

The degradation of plant cell walls by ruminants is of major economic importance in the developed as well as developing world. Rumen fermentation is unique in that efficient plant cell wall degradation relies on the cooperation between microorganisms that produce fibrolytic enzymes and the host animal that provides an anaerobic fermentation chamber. Increasing the efficiency with which the rumen microbiota degrades fiber has been the subject of extensive research for at least the last 100 years. Fiber digestion in the rumen is not optimal, as is supported by the fact that fiber recovered from feces is fermentable. This view is confirmed by the knowledge that mechanical and chemical pretreatments improve fiber degradation, as well as more recent research, which has demonstrated increased fiber digestion by rumen microorganisms when plant lignin composition is modified by genetic manipulation. Rumen microbiologists have sought to improve fiber digestion by genetic and ecological manipulation of rumen fermentation. This has been difficult and a number of constraints have limited progress, including: (a) a lack of reliable transformation systems for major fibrolytic rumen bacteria, (b) a poor understanding of ecological factors that govern persistence of fibrolytic bacteria and fungi in the rumen, (c) a poor understanding of which glycolyl hydrolases need to be manipulated, and (d) a lack of knowledge of the functional genomic framework within which fiber degradation operates. In this review the major fibrolytic organisms are briefly discussed. A more extensive discussion of the enzymes involved in fiber degradation is included. We also discuss the use of plant genetic manipulation, application of free-living lignolytic fungi and the use of exogenous enzymes. Lastly, we will discuss how newer technologies such as genomic and metagenomic approaches can be used to improve our knowledge of the functional genomic framework of plant cell wall degradation in the rumen.

Opportunities to improve fiber degradation in the rumen: microbiology, ecology, and genomics

The conversion of straw into feed by basidiomycetes

1.

The solid state fermentation of beech sawdust, reed, rape and sunflower straw and rice husks by Stropharia rugosoannulata, Pleurotus sp. Florida, Pleurotus cornucopiae and Agrocybe aegerita at 25°C for periods of 0–60 days was examined.




2.

All fungi tested can colonize the sterile substrates used. The highest decomposition rate was found with P. cornucopiae on rape (44.5%) and sunflower (43.2%). Relatively low decomposition activity was observed for A. aegerita.




3.

On all substrates tested, the water soluble substances increase after 60 days of solid state fermentation.




4.

Lignolitic activity and in vitro digestibility are strongly dependent on fungal species and the kind of plant waste substrate. Pleurotus sp. Florida and Stropharia rugosoannulata showed good lignin decomposition and increased the in vitro digestibility of all substrates except rice husks. Agrocybe aegerita decomposed lignin only to a small extent and decreased the in vitro digestibility.




5.

All fungi tested decreased the digestibility of rice husks. This effect is probably caused by high incrustation of rice husks with SiO2.

Conversion of different plant waste into feed by basidiomycetes.

Soil samples from an agricultural field contaminated with 10 ppm14C-benz(a)anthracene in glass tubes were brought into contact with cultures of wood-rotting fungi, precultivated on wheat straw substrate. Forty-five strains of white-rot fungi and four brown-rot fungi were tested for their ability to colonize the soil and to mineralize14C-benz(a)anthracene to14CO2 within a 20-week incubation time. Twenty-two white-rot fungi and all brown-rot fungi were unable to colonize the soil. Twenty-three strains of white-rot fungi, all belonging to the genusPleurotus, colonized the soil. During the experiment the noncolonizing fungi and their substrate disintegrated more and more to a nonstructured pulp from which water diffused into the soil. The same phenomenon was observed in the control which contained only straw without fungus and contaminated soil. In samples with colonizing fungi the substrate as well as the mycelia in the soil remained visibly unchanged during the entire experiment. Surprisingly, most samples with fungi not colonizing the soil and the control without fungus liberated between 40 and 58 % of the applied radioactivity as14CO2 whereas the samples with the colonizing fungi respired only 15–25 % as14CO2. This was 3–5 times more14CO2 than that liberated from the control (4.9 %) which contained only contaminated soil without straw and fungus. A similar result was obtained with selected colonizing and noncolonizing fungi and soil contaminated with 10 ppm14C-pyrene. However, in pure culture studies in which14C-pyrene was added to the straw substrate,Pleurotus sp. (P2), as a representative of the colonizing fungi, mineralized 40.3 % of the added radioactivity to14CO2. The noncolonizing fungiDichomitus squalens andFlammulina velutipes liberated only 17.2 or 1.7 %, respectively, as14CO2. These results lead to the hypothesis that the native soil microflora stimulated by the formed products of straw lysis is responsible for high degradation rates found with noncolonizing fungi.

Screening of white-rot fungi for their ability to mineralize polycyclic aromatic hydrocarbons in soil

The degradation of eight unlabeled highly condensed polycyclic aromatic hydrocarbons (PAH) and the mineralization of three 14C-labeled PAH by the white-rot fungus Pleurotus sp. Florida was investigated. Three concentrations containing 50, 250 or 1250 μg each unlabeled PAH/5 g straw were added to sterile sea sand. Selected treatments were added subsequently with 14C-labeled pyrene, benzo[a]anthracene or benzo[a]pyrene. The PAH-loaded sea sand was then mixed into straw substrate and incubated. The disappearance of the unlabeled four-to six-ring PAH: pyrene, benzo[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenz[a,h]anthracene and benzo[ghi]perylene, was determined by high-performance liquid chromatography. After 15 weeks of incubation, the recoveries were less than 25% for initial amounts of 50 μg (controls above 85%). The recoveries of unlabeled PAH increased in the inoculated samples with increasing concentrations applied. No correlation could be determined between the number of condensed rings of the PAH and the recoveries of added PAH. Pleurotus sp. Florida mineralized 53% [14C]pyrene, 25% [14C]benzo[a]anthracene and 39% [14C]benzo[a]pyrene to 14CO2 in the presence of eight unlabeled PAH (50 μg applied) within 15 weeks. During the course of cultivation, Pleurotus sp. Florida degraded more than 40% of the wheat straw substrate. Variation of the initial concentration of PAH did not influence the extent of degradation of the organic matter.

Degradation of eight highly condensed polycyclic aromatic hydrocarbons by Pleurotus sp. Florida in solid wheat straw substrate

SummaryThe digestion of straw by nine higher fungi and the influence of ammonium nitrate supplementation was investigated using loss of organic matter, degradation of lignin and in vitro digestibility as indices of digestion.The decomposition rates of organic matter were influenced differently by ammonium nitrate supplementation. The rates of decomposition by Pleurotus salmoneo stramineus and Pleurotus eryngii decreased, while those of Lentinus edodes and Pleurotus sp. ‘Florida’ increased at low NH4NO3 concentrations, but decreased at higher concentrations. The decomposition rates of Agrocybe aegerita, Stropharia rugosoannulata, Kuehneromyces mutabilis, and Ganoderma applanatum were generally higher than those of the control at all NH4NO3 levels.The ability to degrade lignin varied greatly. Flammulina velutipes did not attack lignin at all while Agrocybe aegerita did only slightly. The highest lignin degradation rate was found with Pleurotus sp. ‘Florida’. The lignin decomposition rates of Lentinus edodes, Pleurotus eryngii and Pleurotus salmoneo stramineus were depressed at all NH4NO3 levels. No correlation between lignin degradation and nitrogen supplementation was found with Ganoderma applanatum and Pleurotus sp. ‘Florida’. Only Agrocybe aegerita could be stimulated with NH4NO3.The in vitro digestibility of the substrate with and without nitrogen supplementation was decreased with Agrocybe aegerita, Flammulina velutipes, and Ganoderma applanatum. All the other fungi enhanced the in vitro digestibility when no NH4NO3 was added to the substrate. At all NH4NO3 levels, the in vitro digestibility was lower than that of the unsupplemented control. At 1.25% NH4NO3 it fell below the fungus free control value.The results are explained in terms of altered relative decomposition rates for organic matter and lignin after nitrogen supplementation.

Frantisek Zadrazil

Papers

The conversion of straw into feed by basidiomycetes

Conversion of different plant waste into feed by basidiomycetes.

Screening of white-rot fungi for their ability to mineralize polycyclic aromatic hydrocarbons in soil

Degradation of eight highly condensed polycyclic aromatic hydrocarbons by Pleurotus sp. Florida in solid wheat straw substrate

The influence of ammonium nitrate supplementation on degradation and in vitro digestibility of straw colonized by higher fungi