Microorganisms inhabiting soils contaminated with heavy metals produce melanin, a dark brown pigment, as a survival strategy. In this study, a melanin-producing bacterium, Acinetobacter sp. ME1, with heavy metal tolerance and plant growth-promoting traits, was isolated from abandoned mine soil. Strain ME1 exhibited growth at concentrations of Zn up to 250 mg/L, Cd and Pb up to 100 mg/L, and Cr up to 50 mg/L. It had the ability to produce the plant hormone indole-3-acetic acid and siderophores along with 1-aminocyclopropane-1-carboxylic acid deaminase and protease activities. Additionally, it showed antioxidant activity, including catalase and 2,2-diphenyl-1-picryhydrazyl (DPPH) scavenging activities. The optimal conditions for melanin production by ME1 were a pH of 7 and a temperature of 35 ℃. At 1000 mg/L, ME1-extracted melanin exhibited DPPH radical scavenging activity of (25.040±0.007)%, a sun protection factor of 15.200±0.260, and 19.6% antibacterial activity against the plant pathogen Xanthomonas campestris. Furthermore, its adsorption capacity was (0.235±0.073) mg/g melanin for Zn and (0.277±0.008) mg/g melanin for Ni. In plants of Brassica chinensis grown under conditions of hydroponic cultivation with single heavy metal contamination of Cd, Zn, Pb, or Cr, the removal efficiency of each heavy metal was improved by 0.1‒1.8 times after 3 d following inoculation with the strain ME1 compared to the plants grown under the same conditions without inoculation. In addition, ME1 inoculation improved the removal efficiency of each heavy metal by 0.1‒1.0 times under multiple heavy metal contamination conditions. These findings suggest that Acinetobacter sp. ME1 could be used to enhance phytoremediation efficiency in heavy metal-contaminated soils. Moreover, the melanin it produces also holds promise in cosmetics, household products, and medical applications due to its photoprotective, antioxidant, and antimicrobial properties.
Acinetobacter/metabolism* ; Biodegradation, Environmental ; Metals, Heavy/metabolism* ; Melanins/metabolism* ; Soil Microbiology ; Antioxidants/metabolism* ; Plant Development ; Soil Pollutants/metabolism* ; Indoleacetic Acids/metabolism*

Mercury (Hg)-contaminated soil poses a significant threat to the environment and human health. Hg-resistant microorganisms have the ability to survive under the stress of inorganic and organic Hg and effectively reduce Hg levels and toxicity. Compared to physical and chemical remediation methods, microbial remediation technologies have garnered increasing attention in recent years due to their lower cost, remarkable efficacy, and minimal environmental impact. This paper systematically elucidates the molecular mechanisms of Hg resistance in microbes, with a focus on their potential applications in phytoremediation of Hg-contaminated soils through plant-microbe interactions. Furthermore, it highlights the critical role of microbes in enhancing the effectiveness of transgenic plants for Hg remediation, aiming to provide a theoretical foundation and scientific basis for the bioremediation of Hg-contaminated soils.
Mercury/toxicity* ; Biodegradation, Environmental ; Soil Pollutants/isolation & purification* ; Soil Microbiology ; Plants, Genetically Modified/metabolism* ; Bacteria/genetics*

The regulation of rhizosphere bacterial community structure and metabolism by plants in municipal solid waste landfills is a key to enhancing the biodegradation of chlorobenzene (CB). In this study, we employed biodiversity and metabolomics methods to systematically analyze the mechanisms of different plant species in regulating the rhizosphere bacterial community structure and metabolic features and then improved the methane (CH₄) oxidation and CB degradation capacity. The results showed that the rhizosphere soil of Rumex acetosa exhibited the highest CH₄ oxidation and CB degradation capacity of 0.08 g/(kg·h) and 1.72×10^-6 g/(L·h), respectively, followed by the rhizosphere soil of Amaranthus spinosus L., with the rhizosphere soil of Broussonetia papyrifera showing the weakest activity. Rumex acetosa promoted the colonization of Methylocaldum in the rhizosphere, and the small-molecule organic amine, such as triethylamine and N-methyl-aniline, secreted from the roots of this plant enhanced the tricarboxylic acid cycle and nicotinamide metabolism, thereby increasing microbial activity and improving CH₄ and CB degradation efficiency. Conversely, cinnamic acid and its derivatives secreted by Broussonetia papyrifera acted as autotoxins, inhibiting microbial activity and exacerbating the negative effects of salt stress on key microbes such as methanotrophs. This study probed into the mechanisms of typical plants growing in landfill cover soil in regulating bacterial ecological functions, offering theoretical support and practical guidance for the plant-microbe joint control of landfill gas pollution.
Biodegradation, Environmental ; Rhizosphere ; Soil Microbiology ; Waste Disposal Facilities ; Chlorobenzenes/metabolism* ; Bacteria/metabolism* ; Soil Pollutants/metabolism* ; Methane/metabolism* ; Plant Roots/microbiology* ; Amaranthus/microbiology* ; Soil

The biological nitrogen removal technology utilizing heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria has shown effectiveness in wastewater treatment. However, the nitrogen removal efficiency of HN-AD bacteria significantly decreases as the salinity increases. To tackle the challenge of treating high-salt and high-nitrogen wastewater, we isolated a moderately halophilic HN-AD strain 5505 from a salt lake in Xinjiang. The strain was identified based on morphological, physiological, and biochemical characteristics and the 16S rRNA gene sequence. Single-factor experiments were carried out with NH₄⁺-N, NO₃^--N, and NO₂^--N as sole or mixed nitrogen sources to study the nitrifying effect, denitrifying effect, and nitrogen metabolism pathway of the strain. The strain was identified as Halomonas sp.. It can grow in the presence of 1%-25% (W/V) NaCl and exhibited efficient nitrogen removal ability in the presence of 3%-8% NaCl. At the optimal NaCl concentration (8%), the strain showed the NH₄⁺-N, NO₃^--N and NO₂^--N removal rates of 100.0%, 94.11% and 74.43%, respectively. Strain 5505 removed inorganic nitrogen mainly by assimilation, which accounted for over 62.68% of total nitrogen removal. In the presence of mixed nitrogen sources, strain 5505 showed a preference for utilizing ammonia, with a potential HN-AD pathway of NH₄⁺→NH₂OH→NO₂^-→NO₃^-→NO₂^-→NO/N₂O/N₂. The findings provide efficient salt-tolerant bacterial resources, enhance our understanding of biological nitrogen removal, and contribute to the nitrogen removal efficiency improvement in the treatment of high-salt and high-nitrogen wastewater.
Halomonas/classification* ; Nitrogen/isolation & purification* ; Denitrification ; Nitrification ; Wastewater/microbiology* ; Aerobiosis ; Biodegradation, Environmental ; Salinity

Chlorobenzene contaminants (CBs) pose a threat to the eco-environment, and functional strains hold considerable potential for the remediation of CB-contaminated sites. To deeply explore the application potential of functional bacteria in the in-situ bioremediation of CBs, this study focused on the biodegradation characteristics and degradation kinetics of CB and 1, 2-dichlorobenzene (1, 2-DCB) in soil by the isolated strain Serratia marcescens TF-1. Additionally, an in-situ remediation trial was conducted with this strain at a chemical industrial site. Batch serum bottle experiments showed that the degradation rate of CB at the concentrations ranging from 20 to 200 mg/L by TF-1 was 0.22-0.66 mol/(g_cell·h), following the Haldane model, with the optimal concentration at 23.12 mg/L. The results from simulated soil degradation experiments indicated that the combined use of TF-1 and sodium succinate (SS) significantly enhanced the degradation of CBs, with the maximum degradation rate of CB reaching 0.104 d^-1 and a half-life of 6.66 d. For 1, 2-DCB, the maximum degradation rate constant was 0.068 7 d^-1, with a half-life of 10.087 d. The in-situ remediation results at the chemically contaminated site demonstrated that the introduction of bacterial inoculant and SS significantly improved the removal of CBs, achieving the removal rates of 84.2%-100% after 10 d. CB, 1, 4-dichlorobenzene (1, 4-DCB), and benzo[a]pyrene were completely removed. Microbial diversity analysis revealed that the in-situ remediation facilitated the colonization of TF-1 and the enrichment of indigenous nitrogen-fixing Azoarcus, which may have played a key role in the degradation process. This study provides a theoretical basis and practical experience for the in situ bioremediation of CBs-contaminated sites.
Chlorobenzenes/isolation & purification* ; Biodegradation, Environmental ; Soil Pollutants/isolation & purification* ; Serratia marcescens/metabolism* ; Industrial Waste ; Soil Microbiology

Environmental Microbiology, as a compulsory foundational course for the major of environmental and ecological engineering. Its knowledge system not only lays a profound theoretical foundation but also evinces a close-knit nexus to practical applications in environmental protection and ecological restoration. This course thus serves as an outstanding platform facilitating both teaching reforms and practical innovations of professional courses. With Environmental Microbiology as a paradigmatic illustration, this paper concentrates on addressing issues like archaic course contents and enervating teaching approaches, with the aspiration of augmenting students' professional acuities, practical dexterities, and innovation and entrepreneurial aptitudes. In light of the aforesaid aim, we initiated an all-encompassing probe into the teaching reform and practicable paradigms from the perspective of amalgamating professional education with innovation-steered stratagems. Across multiple fronts, comprehensive reformative undertakings were implemented, subsuming the optimization and reconfiguration of course contents, the exploration of sundry teaching methodologies, and the scientific erection of an evaluation system. Ultimately, a nascent teaching model dubbed "three-dimensional, six-loop and five-collaborative" was formed. This series of comprehensive and innovative reform measures has not only substantially augmented the profundity and extensiveness of professional knowledge, permeating into the core of disciplinary essence, but also remarkably bolstered students' practical operational capabilities and innovative thinking patterns, thereby catalyzing their transformation into well-rounded individuals with a competitive edge. By virtue of these efforts, a solid foundation has been firmly laid for the teaching reform of Environmental Microbiology and the cultivation of high-caliber environmental professionals in the contemporary era, heralding a new chapter in the development of environmental education.
Environmental Microbiology ; Teaching ; Education, Professional/methods* ; Curriculum

The development of high-throughput sequencing techniques enabled a deeper and more comprehensive understanding of environmental microbiology. Specifically, the third-generation sequencing techniques represented by nanopore sequencing have greatly promoted the development of environmental microbiology research due to its advantages such as long sequencing reads, fast sequencing speed, real-time monitoring of sequencing data, and convenient machine carrying, as well as no GC bias and no PCR amplification requirement. This review briefly summarized the technical principle and characteristics of nanopore sequencing, followed by discussing the application of nanopore sequencing techniques in the amplicon sequencing, metagenome sequencing and whole genome sequencing of environmental microorganisms. The advantages and challenges of nanopore sequencing in the application of environmental microbiology research were also analyzed.
Environmental Microbiology ; High-Throughput Nucleotide Sequencing ; Metagenome ; Nanopore Sequencing ; Nanopores

Petroleum hydrocarbon pollutants are difficult to be degraded, and bioremediation has received increasing attention for remediating the hydrocarbon polluted area. This review started by introducing the interphase adaptation and transport process of hydrocarbon by microbes. Subsequently, the advances made in the identification of hydrocarbon-degrading strains and genes as well as elucidation of metabolic pathways and underpinning mechanisms in the biodegradation of typical petroleum hydrocarbon pollutants were summarized. The capability of wild-type hydrocarbon degrading bacteria can be enhanced through genetic engineering and metabolic engineering. With the rapid development of synthetic biology, the bioremediation of hydrocarbon polluted area can be further improved by engineering the metabolic pathways of hydrocarbon-degrading microbes, or through design and construction of synthetic microbial consortia.
Bacteria/genetics* ; Biodegradation, Environmental ; Hydrocarbons ; Petroleum ; Petroleum Pollution/analysis* ; Soil Microbiology ; Soil Pollutants

Antibiotics are widely used and prevalently distributed in the environment. The issue of antibiotic resistance genes has posed a huge threat to the global public health. Soil is an important sink of antibiotics in the environment. Antibiotic exposure may introduce adverse effects on soil organisms, and bring indirect but potential risks to human health. Therefore, it is urgent to take actions to remediate antibiotics-contaminated soil. This review summarized effects of antibiotics on phenotype growth of plants, physiological characteristics and community structure of animals, composition and structure of microbial communities, and transmission of antibiotic resistance genes among organisms in soil. Additionally, the potential and prospects of employing antibiotic-resistant soil plants, animals, microorganisms, and their combinations to treat antibiotics-contaminated soil were illustrated. Last but not least, the unaddressed issues in this area were proposed, which may provide insights into relevant research directions in the future.
Animals ; Anti-Bacterial Agents/pharmacology* ; Biodegradation, Environmental ; Drug Resistance, Microbial/genetics* ; Humans ; Soil ; Soil Microbiology ; Soil Pollutants

Polycyclic aromatic hydrocarbons (PAHs) are a class of persistent pollutants that are widely distributed in the environment. Due to their stable structure and poor degradability, PAHs exhibit carcinogenic, teratogenic, and mutagenic toxicity to the ecological environment and organisms, thus increasing attentions have been paid to their removals and remediation. Green, safe and economical technologies are widely used in the bioremediation of PAHs-contaminated soil. This article summarizes the present status of PAHs pollution in soil of China from the aspects of origin, migration, fate, and pollution level. Meanwhile, the types of microorganisms and plants capable of degrading PAHs, as well as the underlying mechanisms, are summarized. The features of three major bioremediation technologies, i.e., microbial remediation, phytoremediation, and joint remediation, are compared. Analysis of the interaction mechanisms between plants and microorganisms, selection and cultivation of stress-resistant strains and plants, as well as safety and efficacy evaluation of practical applications, are expected to become future directions in this field.
Biodegradation, Environmental ; Polycyclic Aromatic Hydrocarbons/toxicity* ; Soil ; Soil Microbiology ; Soil Pollutants