Surfactant efficiency on pentachlorophenol-contaminated wastewater enhanced by Pseudomonas putida AJ 785569

Removal of pentachlorophenol and phenanthrene from lignocellulosic biorefinery wastewater by a biocatalytic/biosurfactant system comprising cross-linked laccase aggregates and rhamnolipid

Synthesis and characterization of highly active cross-linked laccase aggregates (CLLAs) were performed and evaluated for removal of pentachlorophenol and phenanthrene from lignocellulosic biorefinery wastewater. Laccase from Tramates versicolor MTCC 138 was insolubilized as CLLAs via precipitation with 70% ammonium sulphate and simultaneous cross-linking with 5 mM glutaraldehyde to obtain activity recovery of 89.1%. Compared to the free laccase, the pH and thermal stability of the prepared CLLAs were significantly higher. At a high temperature of 60 °C, free laccase had a half-life of 0.25 h, while CLLAs had a half-life of 6.2 h. In biorefinery wastewater (pH 7.0), the free and CLLAs were stored for 3 day at a temperature of 30 °C. Free laccase completely lost their initial activity after 60 h; however, the CLLAs retained 39% activity till 72 h. Due to its excellent stability, free laccase and CLLAs were assessed for removing pentachlorophenol and phenanthrene in wastewater. CLLAs could remove 51-58% of pentachlorophenol (PCP) and phenanthrene (PHE) in 24 h. Biosurfactants, including surfactin, sophorolipid, and rhamnolipid, were assessed for their aptitude to improve the removal of organic contaminants in wastewater. Biorefinery wastewater incubated with all surfactants enhanced PCP and PHE removal compared to the no-surfactant controls. Further, 1 μM rhamnolipid significantly amplified pentachlorophenol and phenanthrene removal to 81-93% for free laccase and CLLAs, respectively.

Synthesis of magnetically recyclable porous cross-linked aggregates of Tramates versicolor MTCC 138 laccase for the efficient removal of pentachlorophenol from aqueous solution

The primary objective of this study is to synthesize the magnetically separable highly active porous immobilized laccase for the removal of pentachlorophenol (PCP) in an aqueous solution. Magnetic porous cross-linked enzyme aggregates (Mp-CLEAs) of laccase were synthesized using 1% starch solution with 5 mM glutaraldehyde followed by 10 h of cross-linking time with an activity recovery of 90.85 ± 0.2%. The biocatalytic efficiency of magnetic porous CLEAs (Mp-CLEAs) was 2-fold higher than that of magnetic CLEAs. The synthesized Mp-CLEAs were mechanically stable with enhanced catalytic efficiency, and reusability thus overcoming the mass transfer limitations and enzyme loss. At 40 °C, the thermal stability of the magnetic porous immobilized laccase was improved, with a 602 min half-life compared to 207 min half-life for the free enzyme. Using 40 U/mL of laccase for the removal of 100 ppm of PCP, M-CLEAs, and Mp-CLEAs removed 60.44% and 65.53% of PCP, respectively. Furthermore, to enhance PCP removal, a laccase-aided system was harnessed by optimizing various surfactants and mediators. Of these, 0.1 mM of rhamnolipid and 2,3 dimethoxy phenol had the highest PCP removal rates of 95.12% and 99.41%, respectively, for Mp-CLEAs. This study demonstrates the efficacy of the laccase-surfactant-mediator system for the removal of PCP from the aqueous solution, which can also be proposed for real-time application.

Biodegradation of diethyl phthalate and phthalic acid by a new indigenous Pseudomonas putida

Diethyl phthalate (DEP) is one of the extensively used plasticizers which has been considered a priority hazardous pollutant due to its carcinogenic, endocrine disrupter, and multi-toxic effects on humans. The identification of DEP in different parts of the ecosphere has increased the global community's attention to the elimination of this pollutant in a bio-eco-friendly way. In this research, a novel aerobic bacterial strain nominates as ShA (GenBank accession number: MN298858) capable of consuming DEP as carbon and energy sources, was isolated from the upper phase (0-10 cm) of Anzali international wetland sediments by enrichment culture method. Morphological characteristics and 16S rRNA gene sequence analysis demonstrated that strain ShA belonged to Pseudomonas putida. The substrate utilization test demonstrated that strain ShA was able to grow in mineral salt medium containing dimethyl phthalate (DMP) and phthalic acid (PA) isomers including terephthalic and isophthalic acid. Degradation assay showed strain ShA completely degraded 200 mg/L DEP within 22 h (pH 7.0, 30 °C). Surprisingly, PA as the main intermediate of DEP biodegradation was identified by GC-FID. Moreover, the rapid degradation of 2000 mg/L PA to CO₂ and H₂O was viewed in 22 h by strain ShA. The possible route of DEP degradation was DEP directly to PA and then PA consumption for growth. This study obtained results that provide a great contribution to applying strain ShA in the biodegradation of low molecular weight of PAEs and PA isomers in natural ecosystems. This is the first report of a P. putida strain able to degrade DEP and PA.

Effectiveness of combined tools: adsorption, bioaugmentation and phytoremediation for pesticides removal from wastewater

The aim of this study was the comparison of two process in pentachlorophenol (PCP: 100 mg L-1) removal by combined process bioaugmentation-adsorption and bioaugmentation-phytoremediation in secondary treated wastewater (STWW). The phytoremediation procedure was conducted by using two plants such as Typha angustifolia and Schoenoplectus acutus, and the bioaugmentation procedure was operated by Pseudomonas putida HM 627618 as a plant growth promoting bacteria (PGPR). The adsorption process was performed by palm date activated carbon. The PCP monitoring was assessed by high performance liquid chromatography (HPLC) and the optical density determination at 600 nm (OD600). The performance of the two processes was observed by the determination of total bacteria, chlorophylls and physical and chemical analysis (COD, pH, conductivity, chloride, and organic carbon). The alfalfa seed germination test was conducted to assess the two operational performance procedures. According to the results obtained from the physical and chemical analysis of the treated STWW, there was no significant differences in the pH and in the EC content of the bioaugmentation-phytoremediation treatment, while a significant increase of the EC content was observed in the bioaugmentation-adsorption to 5.08 mS cm-1. The COD value significantly decreased up to 1320 mg L-1 in bioaugmentation-adsorption treatment (control value 2400 mg L-1) and 98 mg L-1 in bioaugmentation-phytoremediation treatment (control value 98 mg L-1). Microbial biomass monitoring of P. putida shows significant greater in both processes in the order of 9.18 and 7.01 Log CFU mL-1 for bioaugmentation-adsorption and bioaugmentation-phytoremediation, respectively. The chlorophyll content in Typha angustifolia and Schoenoplectus acutus significantly decreased after 144 h with the exception of the chlorophyll a content of Schoenoplectus acutus in which the content increased up to 3.31 mg mL-1. Comparing the performance of these two treatments, it was found according to HPLC analysis that the bioaugmentation-adsorption process was more efficient in removing about 97% of PCP after 48 h, against around 90% of PCP after 72 h for the phytoremediation-bioaugmentation. The alfalfa seeds showed a germination rate after the 5th day of incubation of 100% and 95%, respectively for the PCP-non-contaminated and treated STWW, while for wastewater containing PCP the germination was totally inhibited.

Bacterial remediation of pesticide polluted soils: Exploring the feasibility of site restoration

For decades, reclamation of pesticide contaminated sites has been a challenging avenue. Due to increasing agricultural demand, the application of synthetic pesticides could not be controlled in its usage, and it has now adversely impacted the soil, water, and associated ecosystems posing adverse effects on human health. Agricultural soil and pesticide manufacturing sites, in particular, are one of the most contaminated due to direct exposure. Among various strategies for soil reclamation, ecofriendly microbial bioremediation suffers inherent challenges for large scale field application as interaction of microbes with the polluted soil varies greatly under climatic conditions. Methodically, starting from functional or genomic screening, enrichment isolation; functional pathway mapping, production of tensioactive metabolites for increasing the bioavailability and bio-accessibility, employing genetic engineering strategies for modifications in existing catabolic genes to enhance the degradation activity; each step-in degradation study has challenges and prospects which can be addressed for successful application. The present review critically examines the methodical challenges addressing the feasibility for restoring and reclaiming pesticide contaminated sites along with the ecotoxicological risk assessments. Overall, it highlights the need to fine-tune the available processes and employ interdisciplinary approaches to make microbe assisted bioremediation as the method of choice for reclamation of pesticide contaminated sites.

Unraveling the complex regulatory networks in biofilm formation in bacteria and relevance of biofilms in environmental remediation

Biofilms are assemblages of bacteria embedded within a matrix of extracellular polymeric substances (EPS) attached to a substratum. The process of biofilm formation is a complex phenomenon regulated by the intracellular and intercellular signaling systems. Various secondary messenger molecules such as cyclic dimeric guanosine 3',5'-monophosphate (c-di-GMP), cyclic adenosine 3',5'-monophosphate (cAMP), and cyclic dimeric adenosine 3',5'-monophosphate (c-di-AMP) are involved in complex signaling networks to regulate biofilm development in several bacteria. Moreover, the cell to cell communication system known as Quorum Sensing (QS) also regulates biofilm formation via diverse mechanisms in various bacterial species. Bacteria often switch to the biofilm lifestyle in the presence of toxic pollutants to improve their survivability. Bacteria within a biofilm possess several advantages with regard to the degradation of harmful pollutants, such as increased protection within the biofilm to resist the toxic pollutants, synthesis of extracellular polymeric substances (EPS) that helps in the sequestration of pollutants, elevated catabolic gene expression within the biofilm microenvironment, higher cell density possessing a large pool of genetic resources, adhesion ability to a wide range of substrata, and metabolic heterogeneity. Therefore, a comprehensive account of the various factors regulating biofilm development would provide valuable insights to modulate biofilm formation for improved bioremediation practices. This review summarizes the complex regulatory networks that influence biofilm development in bacteria, with a major focus on the applications of bacterial biofilms for environmental restoration.