Bioremediation of soil long-term contaminated with PAHs by algal-bacterial synergy of Chlorella sp. MM3 and Rhodococcus wratislaviensis strain 9 in slurry phase

The bioremediation of the typical persistent organic pollutants (POPs) by microalgae-bacteria consortia: A systematic review

With industrialisation and the rapidly growing agricultural demand, many organic compounds have been leaked into the environment, causing serious damage to the biosphere. Persistent organic pollutants (POPs) are a type of toxic chemicals that are resistant to degradation through normal chemical, biological or photolytic approaches. With their stable chemical structures, POPs can be accumulated in the environment, and transported through wind and water, causing global environmental issues. Many researches have been conducted to remediate POPs contamination using various kinds of biological methods, and significant results have been seen. Microalgae-bacteria consortium is a newly developed concept for biological technology in contamination treatment, with the synergetic effects between microalgae and bacteria, their potential for pollutants degradation can be further released. In this review, two types of POPs (polychlorinated biphenyls and polycyclic aromatic hydrocarbons) are selected as the targeted pollutants to give a systematic analysis of the biodegradation through microalgae and bacteria, including the species selection, the identification of dominant enzymes, as well as the real application performance of the consortia. In the end, some outlooks and suggestions are given to further guide the development of applying microalgae-bacteria consortia in remediating POPs contamination. In general, the coculturing of microalgae and bacteria is a novel and efficient way to fulfil the advanced treatment of POPs in soil or liquid phase, and both monooxygenase and dioxygenase belonging to oxygenase play a vital role in the biodegradation of PCBs and PAHs. This review provides a general guide in the future investigation of biological treatment of POPs.

Microbes and microbial strategies in carcinogenic polycyclic aromatic hydrocarbons remediation: a systematic review

Degradation, detoxification, or removal of the omnipresent polycyclic aromatic hydrocarbons (PAHs) from the ecosphere as well as their prevention from entering into food chain has never appeared simple. In this context, cost-effective, eco-friendly, and sustainable solutions like microbe-mediated strategies have been adopted worldwide. With this connection, measures have been taken by multifarious modes of microbial remedial strategies, i.e., enzymatic degradation, biofilm and biosurfactant production, application of biochar-immobilized microbes, lactic acid bacteria, rhizospheric-phyllospheric-endophytic microorganisms, genetically engineered microorganisms, and bioelectrochemical techniques like microbial fuel cell. In this review, a nine-way directional approach which is based on the microbial resources reported over the last couple of decades has been described. Fungi were found to be the most dominant taxa among the CPAH-degrading microbial community constituting 52.2%, while bacteria, algae, and yeasts occupied 37.4%, 9.1%, and 1.3%, respectively. In addition to these, category-wise CPAH degrading efficiencies of each microbial taxon, consortium-based applications, CPAH degradation-related molecular tools, and factors affecting CPAH degradation are the other important aspects of this review in light of their appropriate selection and application in the PAH-contaminated environment for better human-health management in order to achieve a sustainable ecosystem.

Biodegradation of benzo[a]pyrene by a marine Chlorella vulgaris LH-1 with heterotrophic ability

In this study, a microalga, Chlorella vulgaris LH-1, with heterotrophic ability to degrade BaP was explored. The effect of BaP concentration on microalga growth was investigated, and the possible biodegradation mechanism of BaP was proposed. Results showed that low BaP concentration (<5 mg/L) had less negative influence on the growth of this microalga under mixotrophic condition, but high BaP concentration (>5 mg/L) had a significant inhibitory effect on its growth. During heterotrophic cultivation, low BaP concentration (<20 mg/L) promoted the growth of C. vulgaris LH-1, whereas high BaP concentration (>20 mg/L) inhibited its growth significantly. The degradation rates of mixotrophic and heterotrophic C. vulgaris LH-1 were 62.56 %-74.13 % and 52.07 %-71.67 %, respectively, when the BaP concentration ranged from 0.5 mg/L to 2 mg/L. The expression of functional enzyme genes of C. vulgaris LH-1 such as phenol 2-monooxygenase activity, protocatechuate 3,4-dioxygenase activity, catechol 1,2-dioxygenase activity, styrene degradation, and benzoate degradation were upregulated in the process of BaP degradation. C. vulgaris LH-1 may degrade BaP by monooxygenase and dioxygenase simultaneously. The degradation of BaP by this microalga under mixotrophic condition goes through the degradation pathway of phthalic acid, whereas it goes through the degradation pathway of benzoic acid under heterotrophic condition.

Isolation and characterization of the aspartame-degrading strain Pseudarthrobacter sp. AS-1

Aspartame is one of the main varieties of artificial sweeteners. Although it has been approved as a food additive, the environmental hazards and ecological risks posed by aspartame are attracting more and more attention. In the present study, strain Pseudarthrobacter sp. AS-1 was isolated and characterized as an efficient aspartame degrader. Strain AS-1 was capable of degrading 200 mg L-1 aspartame within 10 h under conditions optimized at 30 °C and pH 8.0. At the same time, it was found that enzymes degrading aspartame in strain AS-1 were induced and secreted extracellularly. Degradation of aspartame in Pseudarthrobacter sp. AS-1 was identified as following: it was first demethylated to aspartyl-phenylalanine, then degraded to phenylalanine and aspartate, and finally the two amino acids were further degraded. In addition, strain AS-1 was able to remove more than 85% of aspartame in soil and river water. It is the first time that pure bacterial cultures were reported to have the capability of aspartame degradation. These findings add to our knowledge of the microbial metabolic mechanisms of aspartame.

Establishment of evaluation system for biological remediation on organic pollution in groundwater using slow-release agents

In situ bioremediation through slow-release agents can continuously degrade organic pollutants for a long time and have high application potential in solving problems such as tailing and rebound. However, the existing evaluation system is difficult to reflect the performance of bioremediation through slow-release agents, which is not conducive to the promotion of technology. It is urgent to establish a targeted evaluation system. Therefore, based on the multi-criteria decision-making method (MCDA), a comprehensive evaluation model was established. The evaluation index system was constructed for bioremediation through slow-release agents consisting of 16 indicators including pollutant degradation rate, agent preparation cost, engineering operation and maintenance cost, secondary pollution, long-term degradation stability, slow release time, slow release stability, increase in functional microbial flora, increase in total DNA content, agent particle size, solid agent morphology, liquid agent viscosity, dispersibility in aqueous phase, zeta potential, operability of agent preparation, and engineering operation management difficulty. Then, the weight of the indicators was determined by using the best-worst method (BWM), and evaluation criteria was established based on relevant norms and literature. Both and the indicators aggregation simple additive weighting (SAW) method constitute a quantitative evaluation model. The above content together constitutes a new evaluation system for biological remediation on organic pollution in groundwater using slow-release agents, which was defined as AOBS evaluation system. In order to verify the rationality and scientificity of the evaluation system, a typical bioremediation slow-release agent was evaluated using the established AOBS evaluation system. The results showed that the evaluation system could reasonably and comprehensively evaluate bioremediation through slow-release agents and provide suggestions for agent improvement.

Degradation of polycyclic aromatic hydrocarbons in aquatic environments by a symbiotic system consisting of algae and bacteria: green and sustainable technology

Polycyclic aromatic hydrocarbons (PAHs) are genotoxic, carcinogenic, and persistent in the environment and are therefore of great concern in the environmental protection field. Due to the inherent recalcitrance, persistence and nonreactivity of PAHs, they are difficult to remediate via traditional water treatment methods. In recent years, microbial remediation has been widely used as an economical and environmentally friendly degradation technology for the treatment of PAH-contaminated water. Various bacterial and microalgal strains are capable of potentially degrading or transforming PAHs through intrinsic metabolic pathways. However, their biodegradation potential is limited by the cytotoxic effects of petroleum hydrocarbons, unfavourable environmental conditions, and biometabolic limitations. To address this limitation, microbial communities, biochemical pathways, enzyme systems, gene organization, and genetic regulation related to PAH degradation have been intensively investigated. The advantages of algal-bacterial cocultivation have been explored, and the limitations of PAHs degradation by monocultures of algae or bacteria have been overcome by algal-bacterial interactions. Therefore, a new model consisting of a "microalgal-bacterial consortium" is becoming a new management strategy for the effective degradation and removal of PAHs. This review first describes PAH pollution control technologies (physical remediation, chemical remediation, bioremediation, etc.) and proposes an algal-bacterial symbiotic system for the degradation of PAHs by analysing the advantages, disadvantages, and PAH degradation performance in this system to fill existing research gaps. Additionally, an algal-bacterial system is systematically developed, and the effects of environmental conditions are explored to optimize the degradation process and improve its technical feasibility. The aim of this paper is to provide readers with an effective green and sustainable remediation technology for removing PAHs from aquatic environments.

Efficiency, mechanism, influencing factors, and integrated technology of biodegradation for aromatic compounds by microalgae: A review

Aromatic compounds have received widespread attention because of their threat to ecosystem and human health. However, traditional physical and chemical methods are criticized due to secondary pollution and high cost. As a result of ecological security and the ability of carbon sequestration, biodegradation approach based on microalgae has emerged as a promising alternative treatment for aromatic pollutants. In light of the current researches, the degradation efficiency of BTEX (benzene, toluene, ethylbenzene, and xylene), polycyclic aromatic hydrocarbons (PAHs), and phenolic compounds by microalgae was reviewed in this study. We summarized the degradation pathways and metabolites of p-xylene, benzo [a]pyrene, fluorene, phenol, bisphenol A, and nonylphenol by microalgae. The influence factors on the degradation of aromatic compounds by microalgae were also discussed. The integrated technologies based on microalgae for degradation of aromatic compounds were reviewed. Finally, this study discussed the limitations and future research needs of the degradation of these compounds by microalgae.

Effects of terminal electron acceptors on the biodegradation of waste motor oil using Chlorella vulgaris-Rhodococcus erythropolis consortia: Kinetic and thermodynamic windows of opportunity analysis

The Chlorella vulgaris-Rhodococcus erythropolis consortia was constructed for the biodegradation of waste motor oil (WMO), combined with thermodynamic calculations and stoichiometric analyses. The microalgae-bacteria consortium was constructed as C. vulgaris: R. erythropolis = 1:1 (biomass, cell/mL), pH = 7, 3 g/L WMO. Under the same condition, the terminal electron acceptors (TEAs) play a crucial role in the WMO biodegradation, which follows Fe3+ >SO42- > none. The biodegradation of WMO fitted well with the first-order kinetic model under experimental temperatures with different TEAs (R2 >0.98). The WMO biodegradation efficiency reached 99.2 % and 97.1 % with Fe3+ and SO42-as TEAs at 37 °C, respectively. Thermodynamic methanogenesis opportunity windows with Fe3+ as TEA are 2.72 times fold as large as those with SO42-. Microorganism metabolism equations demonstrated the viability of anabolism and catabolism on WMO. This work lays the groundwork for the implementation of WMO wastewater bioremediation and supports research into the biochemical process of WMO biotransformation.

Enhanced biodegradation of phenanthrene and anthracene using a microalgal-bacterial consortium

Polycyclic aromatic hydrocarbons (PAHs) are chemicals that are released into the environment during activities of the petroleum industry. The bioaccumulation, carcinogenic and mutagenic potential of PAHs necessitates the bioremediation of these contaminants. However, bioremediation of PAHs has a number of limitations including the inability of a single microbe to degrade all of the PAH fraction's environmental constituents. Therefore, a different paradigm, employing microalgal-bacterial consortium (MBC), may be used to effectively remove PAHs contaminants. In this type of interaction, the microalgae and bacteria species in the consortium work together in a way that enhances the overall performance of the MBC. Bacterial species in the consortium provide essential nutrients or growth factors by degrading toxic substances and provide these to microalgae, while the microalgae species provide organic carbon for the bacterial species to grow. For the first time, the ability of Gonium pectorale (G. pectorale) microalgae to break down phenanthrene (PHE) and anthracene (ANT) was investigated. Phenanthrene was shown to be more effectively degraded by G. pectorale (98%) as compared to Bacillus licheniformis (B. licheniformis) 19%. Similarly, G. pectorale has effectively degrade anthracene (98%) as compared with B. licheniformis (45%). The consortia of G. pectorale and B. licheniformis has shown a slight increase in the degradation of PHE (96%) and ANT (99%). Our findings show that B. licheniformis did not inhibit the growth of G. pectorale and in the consortia has effectively eliminated the PAHs from the media. Therefore G. pectorale has a tremendous potential to remove PAHs from the polluted environment. Future research will be conducted to assess Gonium's capacity to eliminate PAHs that exhibit high molar masses than that of PHE and ANT.

Update on new trend and progress of the mechanism of polycyclic aromatic hydrocarbon biodegradation by Rhodococcus, based on the new understanding of relevant theories: a review

Rapid industrial and societal developments have led to substantial increases in the use and exploitation of petroleum, and petroleum hydrocarbon pollution has become a serious threat to human health and the environment. Polycyclic aromatic hydrocarbons (PAHs) are primary components of petroleum hydrocarbons. In recent years, microbial remediation of PAHs pollution has been regarded as the most promising and cost-effective treatment measure because of its low cost, robust efficacy, and lack of secondary pollution. Rhodococcus bacteria are regarded as one of main microorganisms that can effectively degrade PAHs because of their wide distribution, broad degradation spectrum, and network-like evolution of degradation gene clusters. In this review, we focus on the biological characteristics of Rhodococcus; current trends in PAHs degradation based on knowledge maps; and the cellular structural, biochemical, and enzymatic basis of degradation mechanisms, along with whole genome and transcriptional regulation. These research advances provide clues for the prospects of Rhodococcus-based applications in environmental protection.

Heavy metal effects on multitrophic level microbial communities and insights for ecological restoration of an abandoned electroplating factory site

The response of soil microbes to heavy metal pollution provides a metric to evaluate the soil health and ecological risks associated with heavy metal contamination. However, a multitrophic level perspective of how soil microbial communities and their functions respond to long-term exposure of multiple heavy metals remains unclear. Herein, we examined variations in soil microbial (including protists and bacteria) diversity, functional guilds and interactions along a pronounced metal pollution gradient in a field surrounding an abandoned electroplating factory. Given the stressful soil environment resulting from extremely high heavy metal concentrations and low nutrients, beta diversity of protist increased, but that of bacteria decreased, at high versus low pollution sites. Additionally, the bacteria community showed low functional diversity and redundancy at the highly polluted sites. We further identified indicative genus and "generalists" in response to heavy metal pollution. Predatory protists in Cercozoa were the most sensitive protist taxa with respect to heavy metal pollution, whereas photosynthetic protists showed a tolerance for metal pollution and nutrient deficiency. The complexity of ecological networks increased, but the communication among the modules disappeared with increasing metal pollution levels. Subnetworks of tolerant bacteria displaying functional versatility (Blastococcus, Agromyces and Opitutus) and photosynthetic protists (microalgae) became more complex with increasing metal pollution levels, indicating their potential for use in bioremediation and restoration of abandoned industrial sites contaminated by heavy metals.

Polyaromatic hydrocarbons (PAHs) in the water environment: A review on toxicity, microbial biodegradation, systematic biological advancements, and environmental fate

Polycyclic aromatic hydrocarbons (PAHs) are considered a major class of organic contaminants or pollutants, which are poisonous, mutagenic, genotoxic, and/or carcinogenic. Due to their ubiquitous occurrence and recalcitrance, PAHs-related pollution possesses significant public health and environmental concerns. Increasing the understanding of PAHs' negative impacts on ecosystems and human health has encouraged more researchers to focus on eliminating these pollutants from the environment. Nutrients available in the aqueous phase, the amount and type of microbes in the culture, and the PAHs' nature and molecular characteristics are the common factors influencing the microbial breakdown of PAHs. In recent decades, microbial community analyses, biochemical pathways, enzyme systems, gene organization, and genetic regulation related to PAH degradation have been intensively researched. Although xenobiotic-degrading microbes have a lot of potential for restoring the damaged ecosystems in a cost-effective and efficient manner, their role and strength to eliminate the refractory PAH compounds using innovative technologies are still to be explored. Recent analytical biochemistry and genetically engineered technologies have aided in improving the effectiveness of PAHs' breakdown by microorganisms, creating and developing advanced bioremediation techniques. Optimizing the key characteristics like the adsorption, bioavailability, and mass transfer of PAH boosts the microorganisms' bioremediation performance, especially in the natural aquatic water bodies. This review's primary goal is to provide an understanding of recent information about how PAHs are degraded and/or transformed in the aquatic environment by halophilic archaea, bacteria, algae, and fungi. Furthermore, the removal mechanisms of PAH in the marine/aquatic environment are discussed in terms of the recent systemic advancements in microbial degradation methodologies. The review outputs would assist in facilitating the development of new insights into PAH bioremediation.

Effects of bioaugmentation by isolated Achromobacter xylosoxidans BP1 on PAHs degradation and microbial community in contaminated soil

Polycyclic aromatic hydrocarbons (PAHs) are a group of organic pollutants ubiquitous and persistent in soil. In order to provide a viable solution for bioremediation of PAHs-contaminated soil, a strain of Achromobacter xylosoxidans BP1 with superior PAHs degradation ability was isolated from contaminated soil at a coal chemical site in northern China. The degradation of phenanthrene (PHE) and benzo[a]pyrene (BaP) by strain BP1 was investigated in three different liquid phase cultures, and the removal rates of PHE and BaP by strain BP1 were 98.47% and 29.86% after 7 days under the conditions of PHE and BaP as the only carbon source, respectively. In the medium with the coexistence of PHE and BaP, the removal rates of BP1 were 89.44% and 9.42% after 7 days, respectively. Then, strain BP1 was investigated for its feasibility in remediating PAH-contaminated soil. Among the four PAHs-contaminated soils treated differently, the treatment inoculated with BP1 exhibited higher removal rates of PHE and BaP (p < 0.05), especially the CS-BP1 treatment (inoculation of BP1 into unsterilized PAHs-contaminated soil) showed 67.72%, 13.48% removal of PHE and BaP, respectively, over 49 days of incubation. Bioaugmentation also significantly increased the activity of dehydrogenase and catalase in the soil (p＜0.05). Furthermore, the effect of bioaugmentation on the removal of PAHs was investigated by measuring the activity of dehydrogenase (DH) and catalase (CAT) during incubation. Among them, the DH and CAT activities of CS-BP1 and SCS-BP1 (inoculation of BP1 into sterilized PAHs-contaminated soil) treatments inoculated with strain BP1 were significantly higher than those of treatments without BP1 addition during incubation (p < 0.01). The structure of the microbial community varied among treatments, but the Proteobacteria phylum showed the highest relative abundance in all treatments of the bioremediation process, and most of the bacteria with higher relative abundance at the genus level also belonged to the Proteobacteria phylum. Prediction of microbial functions in soil by FAPROTAX analysis showed that bioaugmentation enhanced microbial functions associated with the degradation of PAHs. These results demonstrate the effectiveness of Achromobacter xylosoxidans BP1 as a PAH-contaminated soil degrader for the risk control of PAHs contamination.

Integrative effects of microbial inoculation and amendments on improved crop safety in industrial soils co-contaminated with organic and inorganic pollutants

Soils co-contaminated by organic and inorganic pollutants usually pose major ecological risks to soil ecosystems including plants. Thus, effective strategies are needed to alleviate the phytotoxicity caused by such co-contamination. In this study, microbial agents (a mixture of Bacillus subtilis, Sphingobacterium multivorum, and a commercial microbial product named OBT) and soil amendments (β-cyclodextrin, rice husk, biochar, calcium magnesium phosphate fertilizer, and organic fertilizer) were evaluated to determine their applicability in alleviating toxicity to crops (maize and soybean) posed by polycyclic aromatic hydrocarbon (PAHs) and potentially toxic metals co-contaminated soils. The results showed that peroxidase, catalase, and superoxide dismutase activity levels in maize or soybean grown in severely or mildly contaminated soils were significantly enhanced by the integrative effects of amendments and microbial agents, compared with those in single plant treatments. The removal rates of Zn, Pb, and Cd in severely contaminated soils were 49 %, 47 %, and 51 % and 46 %, 45 %, and 48 %, for soybean and maize, respectively. The total contents of Cd, Pb, Zn, and PAHs in soil decreased by day 90. Soil organic matter content, levels of nutrient elements, and enzyme activity (catalase, urease, and dehydrogenase) increased after the amendments and application of microbial agents. Moreover, the amendments and microbial agents also increased the diversity and distribution of bacterial species in the soil. These results suggest that the amendments and microbial agents were beneficial for pollutant purification, improving the soil environment and enhancing both plant resistance to pollutants and immune systems of plants.

The Potential of Microalgae-Bacteria Consortia to Restore Degraded Soils

Soil restoration is one of the biggest challenges of this century. Besides the negative impacts of climate change, the current increase in food demands has put severe pressure on soil resources, resulting in a significant area of degraded land worldwide. However, beneficial microorganisms, such as microalgae and plant growth-promoting bacteria, have an outstanding ability to restore soil health and fertility. In this mini-review, we summarize state-of-the-art knowledge on these microorganisms as amendments that are used to restore degraded and contaminated soils. Furthermore, the potential of microbial consortia to maximize beneficial effects on soil health and boost the production of plant-growth-promoting compounds within a mutualistic interaction is discussed.

Removal of parabens from wastewater by Chlorella vulgaris-bacteria co-cultures

Anthropogenic activities have increased the dispersal of emerging contaminants (ECs), particularly of parabens, causing an escalation of their presence in wastewater (WW). Current WW technologies do not present satisfactory efficiency or sustainability in removing these contaminants. However, bioremediation with microalgae-based systems is proving to be a relevant technology for WW polishing, and the use of microalgae-bacteria consortia can improve the efficiency of WW treatment. This work aimed to study dual cultures of selected bacteria (Raoultella ornithinolytica, Acidovorax facilis, Acinetobacter calcoaceticus, Leucobacter sp. or Rhodococcus fascians) and the microalga Chlorella vulgaris in microbial growth and WW bioremediation - removal of methylparaben (MetP) and nutrients. The association with the bacteria was antagonistic for C. vulgaris biomass productivity as a result of the decreased growth kinetics in comparison to the axenic microalga. The presence of MetP did not disturb the growth of C. vulgaris under axenic or co-cultured conditions, except when associated with R. fascians, where growth enhancement was observed. The removal of MetP by the microalga was modest (circa 30 %, with a removal rate of 0.0343 mg/L.d), but increased remarkably when the consortia were used (> 50 %, with an average removal rate > 0.0779 mg/L.d), through biodegradation and photodegradation. For nutrient removal, the consortia were found to be less effective than the axenic microalga, except for nitrogen (N) removal by C. vulgaris w/ R. fascians. The overall results propose that C. vulgaris co-cultivation with bacteria can increase MetP removal, while negatively affecting the microalga growth and the consequent reduction of sludge production, highlighting the potential of microalgae-bacteria consortia for the effective polishing of WW contaminated with parabens.

Polyethylene mulching film degrading bacteria within the plastisphere: Co-culture of plastic degrading strains screened by bacterial community succession

As an ecological niche close to the polymer, microorganisms in the plastisphere possess the advantage of degrading plastics. This study aims to investigate the bacterial community succession and obtain degrading bacteria in the plastisphere, as well as identify the most efficient degradation combination by co-culture of multiple strains. The findings demonstrate the alpha-diversity indices of the plastisphere bacterial community are significantly lower, and the community structure is regularly and significantly altered. With the time of culture, the plastisphere community composition alters regularly, and the hydrocarbon-degrading genera become the core members. Functional prediction of community reveals the potential for Xenobiotics Biodegradation and Metabolism of plastisphere, and the apparent variations detections of polyethylene mulching film (PMF) indicating the PMF degrading ability of plastisphere. Besides, three PMF-degrading bacterial strains, Rhodopseudomonas sp. P1 (P), Rhodanobacter sp. Rs (R) and Microbacterium sp. M1 (M), are screened for co-culture with PMF degrading strain Bacillus aryabhattai 5-3 (B). By considering bacterial growth, biofilm adhesion, and apparent degradation of different samples, RB (R. sp. Rs + B. aryabhattai 5-3) is ultimately selected as the best PMF degradation combination. This study provides a new possibility for plastisphere-related research from the perspective of mitigating plastic pollution on agricultural land.

Iron-dependent mutualism between Chlorella sorokiniana and Ralstonia pickettii forms the basis for a sustainable bioremediation system

Phototrophic communities of autotrophic microalgae and heterotrophic bacteria perform complex tasks of nutrient acquisition and tackling environmental stress but remain underexplored as a basis for the bioremediation of emerging pollutants. In industrial monoculture designs, poor iron uptake by microalgae limits their productivity and biotechnological efficacy. Iron supplementation is expensive and ineffective because iron remains insoluble in an aqueous medium and is biologically unavailable. However, microalgae develop complex interkingdom associations with siderophore-producing bacteria that help solubilize iron and increase its bioavailability. Using dye degradation as a model, we combined environmental isolations and synthetic ecology as a workflow to design a simplified microbial community based on iron and carbon exchange. We established a mutualism between the previously non-associated alga Chlorella sorokiniana and siderophore-producing bacterium Ralstonia pickettii. Siderophore-mediated increase in iron bioavailability alleviated Fe stress for algae and increased the reductive iron uptake mechanism and bioremediation potential. In exchange, C. sorokiniana produced galactose, glucose, and mannose as major extracellular monosaccharides, supporting bacterial growth. We propose that extracellular iron reduction by ferrireductase is crucial for azoreductase-mediated dye degradation in microalgae. These results demonstrate that iron bioavailability, often overlooked in cultivation, governs microalgal growth, enzymatic processes, and bioremediation potential. Our results suggest that phototrophic communities with an active association for iron and carbon exchange have the potential to overcome challenges associated with micronutrient availability, while scaling up bioremediation designs.

Complete Genome Sequence of Rhodococcus sp. Strain 9, Isolated from Contaminated Australian Groundwater

Here, we report the 7.7-Mbp genome sequence of Rhodococcus sp. strain 9, which was isolated from Australian groundwater contaminated with phenols and trichloroethylene. This strain has previously been shown to efficiently degrade p-nitrophenol and high-molecular-weight polycyclic aromatic hydrocarbons (PAHs).

Efficient bioremediation of PAHs-contaminated soils by a methylotrophic enrichment culture

Bioaugmentation effectively enhances microbial bioremediation of hazardous polycyclic aromatic hydrocarbons (PAHs) from contaminated environments. While screening for pyrene-degrading bacteria from a former manufactured gas plant soil (MGPS), the mixed enrichment culture was found to be more efficient in PAHs biodegradation than the culturable pure strains. Interestingly, analysis of 16S rRNA sequences revealed that the culture was dominated by a previously uncultured member of the family Rhizobiaceae. The culture utilized C1 and other methylotrophic substrates, including dimethylformamide (DMF), which was used as a solvent for supplementing the culture medium with PAHs. In the liquid medium, the culture rapidly degraded phenanthrene, pyrene, and the carcinogenic benzo(a)pyrene (BaP), when provided as the sole carbon source or with DMF as a co-substrate. The efficiency of the culture in the bioremediation of PAHs from the MGPS and a laboratory waste soil (LWS) was evaluated in bench-scale slurry systems. After 28 days, 80% of Σ16 PAHs were efficiently removed from the inoculated MGPS. Notably, the bioaugmentation achieved 90% removal of four-ringed and 60% of highly recalcitrant five- and six-ringed PAHs from the MGPS. Likewise, almost all phenanthrene, pyrene, and 65% BaP were removed from the bioaugmented LWS. This study highlights the application of the methylotrophic enrichment culture dominated by an uncultured bacterium for the efficient bioremediation of PAHs.

Bioremediation of PAHs and heavy metals co-contaminated soils: Challenges and enhancement strategies

Systemic studies on the bioremediation of co-contaminated PAHs and heavy metals are lacking, and this paper provides an in-depth review on the topic. The released sources and transport of co-contaminated PAHs and heavy metals, including their co-occurrence through formation of cation-π interactions and their adsorption in soil are examined. Moreover, it is investigated that co-contamination of PAHs and heavy metals can drive a synergistic positive influence on bioremediation through enhanced secretion of extracellular polymeric substances (EPSs), production of biosynthetic genes, organic acid and enzymatic proliferation. However, PAHs molecular structure, PAHs-heavy metals bioavailability and their interactive cytotoxic effects on microorganisms can exert a challenging influence on the bioremediation under co-contaminated conditions. The fluctuations in bioavailability for microorganisms are associated with soil properties, chemical coordinative interactions, and biological activities under the co-contaminated PAHs-heavy metals conditions. The interactive cytotoxicity caused by the emergence of co-contaminants includes microbial cell disruption, denaturation of DNA and protein structure, and deregulation of antioxidant biological molecules. Finally, this paper presents the emerging strategies to overcome the bioavailability problems and recommends the use of biostimulation and bioaugmentation along with the microbial immobilization for enhanced bioremediation of PAHs-heavy metals co-contaminated sites. Better knowledge of the bioremediation potential is imperative to improve the use of these approaches for the sustainable and cost-effective remediation of PAHs and heavy metals co-contamination in the near future.

A review on the enzymes and metabolites identified by mass spectrometry from bacteria and microalgae involved in the degradation of high molecular weight PAHs

High molecular weight PAHs (HMW PAHs) are dangerous pollutants widely distributed in the environment. The use of microorganisms represents an important tool for HMW PAHs bioremediation, so, the understanding of their biochemical pathways facilitates the development of biodegradation strategies. For this reason, the potential role of species of microalgae, bacteria, and microalga-bacteria consortia in the degradation of HMW PAHs is discussed. The identification of their metabolites, mostly by GC-MS and LC-MS, allows a better approach to the enzymes involved in the key steps of the metabolic pathways of HMW PAHs biodegradation. So, this review intends to address the proteomic research on enzyme activities and their involvement in regulating essential biochemical functions that help bacteria and microalgae in the biodegradation processes of HMW PAHs. It is noteworthy that, given that to the best of our knowledge, this is the first review focused on the mass spectrometry identification of the HMW PAHs metabolites; whereby and due to the great concern of the presence of HMW PAHs in the environment, this material could help the urgency of developing new bioremediation methods. The elucidation of the metabolic pathways of persistent pollutant degrading microorganisms should lead to a better knowledge of the enzymes involved, which could contribute to a very ecological route to the control of environmental contamination in the future.

Bioremediation of aromatic hydrocarbons contaminated soil from industrial site using surface modified amino acid enhanced biosurfactant

Surface modified lipopeptide biosurfactant (BS) with enhancement of amino acids was produced using Bacillus Malacitensis. The aromatic hydrocarbons from contaminated soil were removed by BS soil washing process and bioremediation using activated functionalized carbon-BS matrix (AFC-BS). The Central Composite Design (CCD) showed the optimum time100 h; pH 7; temperature 30°C on maximum yield of BS. The amino acid profiling of BS reveals the enhancement of amino acids especially polar amino acids and its importance in the formation of micellar structure for the tight packing of aromatic hydrocarbons from industrial contaminated soil. AFC-BS matrix was implanted directly into the contaminated soil for 28 days and found 61.80 % of Total Petroleum Hydrocarbon (TPH) removal efficiency which is high compared to the AFC treated soil. The compounds were extracted from contaminated soil and AFC-BS matrix, found similar peaks in high performance liquid chromatography, which reveals the ability of BS to remove aromatic contaminants. The soil toxicity was also analyzed by seed germination and found improvement in the growth of seeds. The germination of seeds increased from 60 % to 100 % and the phytotoxicity of root and shoot was reduced from 89.50 %, 88.45 % to12.55 %, 11.87 % respectively.

Toxicity of Naphthenic Acids on the Chlorophyll Fluorescence Parameters and Antioxidant Enzyme Activity of Heterosigma akashiwo

Petroleum hydrocarbons can serve as a carbon source for marine phytoplankton; so, marine high-acid crude oil pollution events are likely to result in algal outbreaks or harmful algal blooms (HABs) in surface waters. Naphthenic acids (NAs) are the primary acidic component of crude oil, and red tide is of great concern due to its high diffusivity and strong destructive properties. It is important to study the mechanism of the toxic effect of NAs on the typical red tide algae, Heterosigma akashiwo, for the balance and stability of marine algae. The mechanism of NAs’ damage effect was investigated in terms of the antioxidant enzyme activity, cell number, the chlorophyll positive fluorescence parameters, and the cell morphology of microalgae. Experiments confirmed the hormesis of low-concentration (0.5, 2, and 4 mg/L) NAs on Heterosigma akashiwo, and the indicators of high-concentration (8 and 16 mg/L) NA exposures showed inhibition. In this study, the toxic effect of NAs on the target organism showed a clear concentration–dose relationship. The 16 mg/L NAs stress caused severe damage to the morphology and structure of the target biological cells in a short time (96 h), and the population growth decreased. The target organisms showed a staged oxidative stress response to NAs. The behavior in the low-concentration treatment groups showed toxicant excitatory effects on the photosynthetic efficiency and antioxidant enzyme activity of the target organisms. This study provides theoretical and practical data for the development of an important toxicological model of the toxicant’s excitement effects and antioxidant defense mechanisms. In addition, it provides prospective research data for the prediction and avoidance of ecological risk from NA pollution in marine environments.

The multi metal-resistant bacterium Cupriavidus metallidurans CH34 affects growth and metal mobilization in Arabidopsis thaliana plants exposed to copper

Copper (Cu) is important for plant growth, but high concentrations can lead to detrimental effects such as primary root length inhibition, vegetative tissue chlorosis, and even plant death. The interaction between plant-soil microbiota and roots can potentially affect metal mobility and availability, and, therefore, overall plant metal concentration. Cupriavidus metallidurans CH34 is a multi metal-resistant bacterial model that alters metal mobility and bioavailability through ion pumping, metal complexation, and reduction processes. The interactions between strain CH34 and plants may affect the growth, metal uptake, and translocation of Arabidopsis thaliana plants that are exposed to or not exposed to Cu. In this study, we looked also at the specific gene expression changes in C. metallidurans when co-cultured with Cu-exposed A. thaliana. We found that A. thaliana’s rosette area, primary and secondary root growth, and dry weight were affected by strain CH34, and that beneficial or detrimental effects depended on Cu concentration. An increase in some plant growth parameters was observed at copper concentrations lower than 50 µM and significant detrimental effects were found at concentrations higher than 50 µM Cu. We also observed up to a 90% increase and 60% decrease in metal accumulation and mobilization in inoculated A. thaliana. In turn, copper-stressed A. thaliana altered C. metallidurans colonization, and cop genes that encoded copper resistance in strain CH34 were induced by the combination of A. thaliana and Cu. These results reveal the complexity of the plant-bacteria-metal triad and will contribute to our understanding of their applications in plant growth promotion, protection, and phytoremediation strategies.

Metabolic interactions in a bacterial co-culture accelerate phenanthrene degradation

A highly eff ;ective phenanthrene (PHE)-degrading co-culture containing Rhodococcus sp. WB9 and Mycobacterium sp. WY10 was constructed and completely degraded 100 mg L^-1 PHE within 36 h, showing improved degradation rate compared to their monocultures. In the co-culture, strain WY10 played a predominant role in PHE degradation. 1-hydroxy-2-naphthoic acid was an end-product of PHE degradation by strain WB9 and accumulated in the culture medium to serve as a substrate for strain WY10 growth, thereby accelerating PHE degradation. In turn, strain WY10 degraded PHE and 1-hydroxy-2-naphthoic acid intracellularly to form phthalate and protocatechuate that were exported to the culture medium through efflux transporters. However, strain WY10 cannot take up extracellular phthalate due to the absence of phthalate transporters, restricting phthalate degradation and PHE mineralization. In the co-culture, phthalate and protocatechuate accumulated in the culture medium were taken up and degraded towards TCA cycle by strain WB9. Therefore, the metabolic cross-feeding of strains WB9 and WY10 accelerated PHE degradation and mineralization. These findings exhibiting the synergistic degradation of PHE in the bacterial co-culture will facilitate its bioremediation application.

Recent Advances in the Study of the Remediation of Polycyclic Aromatic Compound (PAC)-Contaminated Soils: Transformation Products, Toxicity, and Bioavailability Analyses

Polycyclic aromatic compounds (PACs) encompass a diverse group of compounds, often found in historically contaminated sites. Different experimental techniques have been used to remediate PACs-contaminated soils. This brief review surveyed over 270 studies concerning remediation of PACs-contaminated soils and found that, while these studies often measured the concentration of 16 parent polycyclic aromatic hydrocarbons (PAHs) pre- and post-remediation, only a fraction of the studies included the measurement of PAC-transformation products (PAC-TPs) and other PACs (n = 33). Only a few studies also incorporated genotoxicity/toxicity/mutagenicity analysis pre- and post-remediation (n = 5). Another aspect that these studies often neglected to include was bioavailability, as none of the studies that included measurement of PAH-TPs and PACs included bioavailability investigation. Based on the literature analysis, future remediation studies need to consider chemical analysis of PAH-TPs and PACs, genotoxicity/toxicity/mutagenicity, and bioavailability analyses pre- and post-remediation. These assessments will help address numerous concerns including, among others, the presence, properties, and toxicity of PACs and PAH-TPs, risk assessment of soil post-remediation, and the bioavailability of PAH-TPs. Other supplementary techniques that help assist these analyses and recommendations for future analyses are also discussed.

Enhancement of phenol biodegradation: Metabolic division of labor in co-culture of Stenotrophomonas sp. N5 and Advenella sp. B9

The aim of this work is to study the synergistic effect of Stenotrophomonas sp. N5 and Advenella sp. B9 co-culture (COC) on enhancement of phenol biodegradation. These two strains utilizing phenol as sole carbon and energy source were isolated from phenol-containing coking wastewater. The results of biodegradation experiment showed the COC of N5 and B9 has stronger capability to degrade phenol than either of mono-culture (MOC). Growth kinetics studies indicated inhibitory effect of phenol on COC was reduced by the interaction of N5 and B9 in COC. The RNA-Seq results demonstrated that phenol biodegradation was enhanced by metabolic division of labor (DOL) in COC based on the expression of key genes for phenol degradation. GO enrichment analysis of differentially expressed genes (DEGs) indicated DEGs between COC and MOC degradation systems are mainly concentrated in the synthesis of cell components, microbial growth and metabolism, and catalytic activity. The expression of 3 transcriptional factors (LysR, Two-component system response regulator, and TetR families) which can regulate degradation of aromatic compounds, was identified beneficial to phenol degradation.

Polycyclic Aromatic Hydrocarbons: Sources, Toxicity, and Remediation Approaches

Polycyclic aromatic hydrocarbons (PAHs) are widespread across the globe mainly due to long-term anthropogenic sources of pollution. The inherent properties of PAHs such as heterocyclic aromatic ring structures, hydrophobicity, and thermostability have made them recalcitrant and highly persistent in the environment. PAH pollutants have been determined to be highly toxic, mutagenic, carcinogenic, teratogenic, and immunotoxicogenic to various life forms. Therefore, this review discusses the primary sources of PAH emissions, exposure routes, and toxic effects on humans, in particular. This review briefly summarizes the physical and chemical PAH remediation approaches such as membrane filtration, soil washing, adsorption, electrokinetic, thermal, oxidation, and photocatalytic treatments. This review provides a detailed systematic compilation of the eco-friendly biological treatment solutions for remediation of PAHs such as microbial remediation approaches using bacteria, archaea, fungi, algae, and co-cultures. In situ and ex situ biological treatments such as land farming, biostimulation, bioaugmentation, phytoremediation, bioreactor, and vermiremediation approaches are discussed in detail, and a summary of the factors affecting and limiting PAH bioremediation is also discussed. An overview of emerging technologies employing multi-process combinatorial treatment approaches is given, and newer concepts on generation of value-added by-products during PAH remediation are highlighted in this review.

Hazardous wastes treatment technologies

A review of the literature published in 2019 on topics related to hazardous waste management in water, soils, sediments, and air. The review covered treatment technologies applying physical, chemical, and biological principles for the remediation of contaminated water, soils, sediments, and air. PRACTICAL POINTS: This report provides a review of technologies for the management of waters, wastewaters, air, sediments, and soils contaminated by various hazardous chemicals including inorganic (e.g., oxyanions, salts, and heavy metals), organic (e.g., halogenated, pharmaceuticals and personal care products, pesticides, and persistent organic chemicals) in three scientific areas of physical, chemical, and biological methods. Physical methods for the management of hazardous wastes including general adsorption, sand filtration, coagulation/flocculation, electrodialysis, electrokinetics, electro-sorption ( capacitive deionization, CDI), membrane (RO, NF, MF), photocatalysis, photoelectrochemical oxidation, sonochemical, non-thermal plasma, supercritical fluid, electrochemical oxidation, and electrochemical reduction processes were reviewed. Chemical methods including ozone-based, hydrogen peroxide-based, potassium permanganate processes, and Fenton and Fenton-like process were reviewed. Biological methods such as aerobic, anoxic, anaerobic, bioreactors, constructed wetlands, soil bioremediation and biofilter processes for the management of hazardous wastes, in mode of consortium and pure culture were reviewed. Case histories were reviewed in four areas including contaminated sediments, contaminated soils, mixed industrial solid wastes and radioactive wastes.