Editorial: Microbial Regulatory Mechanisms in Remediation of Industrial Wastewater and Contaminated Soils

Rui Liu ^1* Yuling Zhang ² Weitao Liu ³ Jianjun Chen ^4*

• ¹ Yunnan University, Kunming, Yunnan Province, China
• ² Jilin University, Changchun, Hebei Province, China
• ³ Nankai University, Tianjin, China
• ⁴ University of Florida, Gainesville, United States

Superalloy electrolytes are acidic solutions used to dissolve and machine superalloys. Such solutions generally contain significant quantities of precious metals. Yang et al. evaluated five fungal strains for adsorption of heavy metal ions. Paecilomyces lilacinus was identified as the most effective strain, adsorbing 37. 1,64.4,47.9,41.6,and 25.4% of Co,Cr,Mo,Re,and Ni in one hour, respectively, under a pH of 5. Based on Fourier transform infrared spectroscopy, the fungal surface function groups: hydroxyl (-OH), amino (-NH2), amide (-CONH2), carbonyl (-C = O), carboxyl (-COOH), and phosphate (PO4 3-) participated in the adsorption process.Biomineralization is another mechanism that microbes use to remediate heavy metals. Zhu et al. investigated the role of phosphate-solubilizing bacteria (PSB) and urease-producing bacteria (UPB), comprising six Bacillus strains, in stabilizing heavy metals. PSB can dissolve insoluble phosphorus, leading to the precipitation of metal ions; UPB can hydrolyze urea to produce carbonate ions that contribute to the formation of carboxylate metal complexes. Synergistic effects were noticed using both PSB and UPB strains, resulting in more than 92% stabilization rates for Cu, Zn, Cd, and Pb, respectively. The biomineralized products were mainly carbonate and phosphate precipitates.Cyanobacteria are photoautotrophic species that possess remarkable abilities to remediate heavy metals. In addition to biosorption, this group of bacteria can take up metals from the environment and accumulate them inside cells by detoxification, compartmentation, and transformation because they have no extensive internal-bound membranes. Lourembam et al. reviewed the potential of cyanobacteria in the biosorption, bioaccumulation, and sequestration of heavy metals on the surface and inside of cells, providing the current status and future perspectives on the use of cyanobacteria to remediate heavy metals.Refractory organic pollutants are another group of contaminants in the environment. Microbes are the most effective agents for remediating these pollutants as they can break them into less toxic or harmless compounds. Li et al. reported that Candida tropicalis SHC-03 was able to grow in phenol as the sole source of carbon and shift from carbohydrate metabolism to an enhanced phenol degradation pathway, which was enhanced by the significant upregulation of genes encoding phenol 2-monooxygenase and catechol 1,2-dioxygenase. The phenol degradation rates were 99.5 and 95.9% at the phenol concentrations of 1.6 and 1.8 g/L, respectively.Pesticides are widely used to control pest insects. However, the extensive application has raised concerns over contamination of the environment. Faridy et al. isolated three bacterial consortia, FD, TD, and MD, from paddy soils. These species were predominant in the Azospirillum, Ochrobactrum, Sphingobium, and Sphingomonas genera. All three consortia could biodegrade more than 80% of fipronil (FIP), thiobencarb (THIO), or FIP + THIO in 10 days through oxidative and hydrolytic processes.Conventional and biodegradable microplastics widely occur in oceans, freshwater, and sediments, potentially harming humans. Microbes can remediate microplastic by biodegradation. In nature, microplastics are colonized by biofilm-forming microbes, and different microplastics may host different microbes. Jiao et al. found that most microbes colonizing conventional microplastics had nitrification and denitrification properties. In contrast, dominant bacteria on biodegradable microplastics were able to degrade lignin, cellulose, and carbon metabolism. The differences in bacterial communities were largely related to the intrinsic properties of the materials themselves, along with changes in the physical-chemical attributes of the sediments.Dinitrophenols (DNP) are a class of synthetic organic compounds used to manufacture dye and explosives. Soil-buried landmines containing DNP could be dangerous to personnel. Kim et al. studied the responses of the YhaJ transcription factor in E. coli strain K-12 to DNP and its metabolic products since a small amount of DNP byproduct vapor emitted from the landmines can be detected by Yhaj-based biosensors. By the mutation of the DNA binding domain of Yhaj, a mutant known as S23R had increased biosensor ability to DNP. This study signifies the importance of genetic manipulation of microbes in improving bioremediation efficiency.In summary, microbes represent affordable agents for the remediation of environmental pollutants. Papers published in this Research Topic highlight recent progress in microbial remediation of heavy metals and organic compounds in waterbodies and soils. Reported mechanisms for heavy metal remediation mainly involve biosorption. Future research on manipulating ion transporters, the process of detoxification, ion chelation, and compartmentation should be emphasized. Microbial remediation of organic pollutants should also tackle novel biodegradation pathways and genetic engineering of key genes in the pathway to enhance remediation efficiency.