Assessment of Different Spent Mushroom Substrates to Bioremediate Soils Contaminated with Petroleum Hydrocarbons

Bioremediation of petroleum hydrocarbons polluted soil by spent mushroom substrates: Microbiological structure and functionality

Spent mushroom substrate (SMS) holds valuable microbiota that can be useful in remediating polluted soils with hydrocarbons. However, the microorganisms behind the bioremediation process remain uncertain. In this work, a bioremediation assay of total petroleum hydrocarbons (TPHs) polluted soil by SMS application was performed to elucidate the microorganisms and consortia involved in biodegradation by a metabarcoding analysis. Untreated polluted soil was compared to seven bioremediation treatments by adding SMS of Agaricus bisporus, Pleurotus eryngii, Pleurotus ostreatus, and combinations. Soil microbial activity, TPH biodegradation, taxonomic classification, and predictive functional analysis were evaluated in the microbiopiles at 60 days. Different metagenomics approaches were performed to understand the impact of each SMS on native soil microbiota and TPHs biodegradation. All SMSs enhanced the degradation of aliphatic and aromatic hydrocarbons, being A. bisporus the most effective, promoting an efficient consortium constituted by the bacterial families Alcanivoraceae, Alcaligenaceae, and Dietziaceae along with the fungal genera Scedosporium and Aspergillus. The predictive 16 S rRNA gene study partially explained the decontamination efficacy by observing changes in the taxonomic structure of bacteria and fungi, and changes in the potential profiles of estimated degradative genes across the different treatments. This work provides new insights into TPHs bioremediation.

Main Factors Determining the Scale-Up Effectiveness of Mycoremediation for the Decontamination of Aliphatic Hydrocarbons in Soil

Soil contamination constitutes a significant threat to the health of soil ecosystems in terms of complexity, toxicity, and recalcitrance. Among all contaminants, aliphatic petroleum hydrocarbons (APH) are of particular concern due to their abundance and persistence in the environment and the need of remediation technologies to ensure their removal in an environmentally, socially, and economically sustainable way. Soil remediation technologies presently available on the market to tackle soil contamination by petroleum hydrocarbons (PH) include landfilling, physical treatments (e.g., thermal desorption), chemical treatments (e.g., oxidation), and conventional bioremediation. The first two solutions are costly and energy-intensive approaches. Conversely, bioremediation of on-site excavated soil arranged in biopiles is a more sustainable procedure. Biopiles are engineered heaps able to stimulate microbial activity and enhance biodegradation, thus ensuring the removal of organic pollutants. This soil remediation technology is currently the most environmentally friendly solution available on the market, as it is less energy-intensive and has no detrimental impact on biological soil functions. However, its major limitation is its low removal efficiency, especially for long-chain hydrocarbons (LCH), compared to thermal desorption. Nevertheless, the use of fungi for remediation of environmental contaminants retains the benefits of bioremediation treatments, including low economic, social, and environmental costs, while attaining removal efficiencies similar to thermal desorption. Mycoremediation is a widely studied technology at lab scale, but there are few experiences at pilot scale. Several factors may reduce the overall efficiency of on-site mycoremediation biopiles (mycopiles), and the efficiency detected in the bench scale. These factors include the bioavailability of hydrocarbons, the selection of fungal species and bulking agents and their application rate, the interaction between the inoculated fungi and the indigenous microbiota, soil properties and nutrients, and other environmental factors (e.g., humidity, oxygen, and temperature). The identification of these factors at an early stage of biotreatability experiments would allow the application of this on-site technology to be refined and fine-tuned. This review brings together all mycoremediation work applied to aliphatic petroleum hydrocarbons (APH) and identifies the key factors in making mycoremediation effective. It also includes technological advances that reduce the effect of these factors, such as the structure of mycopiles, the application of surfactants, and the control of environmental factors.

Isolation of Lead Resistant Bacteria from Spent Mushroom Compost and Their Impact on Growth and Biochemical Parameters of Safflower

Spent mushroom compost (SMC) is a favored waste because of its nutrients for plant growth and useful microbial communities. The aim of this study was to isolate the lead resistant bacteria from SMC and to evaluate the effects of SMC extract on the growth and biochemical parameters of safflower under lead stress including fresh and dry weights, photosynthetic pigments, protein content, and enzymatic activities. Four bacterial strains including Bacillus licheniformis, Bacillus cereus, Bacillus aerius, and Brevibacterium frigoritolerans were identified in the SMC extract; from which B. licheniformis offer the most resistance to lead. The highest total chlorophyll content of the plant was seen by treatment with 100 mM lead; the highest carotenoid content observed by treatment with 100 mM lead in association with 10% and 5% SMC extract; and the highest increase in protein content was seen in the presence of 5% SMC. The safflower seeds germination was reached the highest level in the presence of 20% SMC extract associated with 50 and 100 mM lead. The highest dry weights of the plant roots (33%) and stems (85%) were shown in the presence of 100 mM lead in association with 5% SMC extract. The highest antioxidant enzymes activity was seen by polyphenol oxidase (0.135 OD/min/mg) in the presence of 100 mM lead in association with 10% SMC extract. It is concluded that by induction of lead bioremediation via improving lead resistant bacterial communication, and the addition of 10-20% SMC extract to the agricultural soil, safflower may undergo the lead stress.