Interaction effects of polycyclic aromatic hydrocarbons and heavy metals on a soil microalga, Chlorococcum sp. MM11

The cadmium tolerance and bioaccumulation mechanism of Tetratostichococcus sp. P1: insight from transcriptomics analysis

Cadmium (Cd) has become a severe issue in relatively low concentration and attracts expert attention due to its toxicity, accumulation, and biomagnification in living organisms. Cd does not have a biological role and causes serious health issues. Therefore, Cd pollutants should be reduced and removed from the environment. Microalgae have great potential for Cd absorption for waste treatment since they are more environmentally friendly than existing treatment methods and have strong metal sorption selectivity. This study evaluated the tolerance and ability of the microalga Tetratostichococcus sp. P1 to remove Cd ions under acidic conditions and reveal mechanisms based on transcriptomics analysis. The results showed that Tetratostichococcus sp. P1 had a high Cd tolerance that survived under the presence of Cd up to 100 µM, and IC50, the half-maximal inhibitory concentration value, was 57.0 μM, calculated from the change in growth rate based on the chlorophyll content. Long-term Cd exposure affected the algal morphology and photosynthetic pigments of the alga. Tetratostichococcus sp. P1 removed Cd with a maximum uptake of 1.55 mg g-1 dry weight. Transcriptomic analysis revealed the upregulation of the expression of genes related to metal binding, such as metallothionein. Group A, Group B transporters and glutathione, were also found upregulated. While the downregulation of the genes were related to photosynthesis, mitochondria electron transport, ABC-2 transporter, polysaccharide metabolic process, and cell division. This research is the first study on heavy metal bioremediation using Tetratostichococcus sp. P1 and provides a new potential microalga strain for heavy metal removal in wastewater.[Figure: see text]Abbreviations:BP: Biological process; bZIP: Basic Leucine Zipper; CC: Cellular component; ccc1: Ca (II)-sensitive cross complementary 1; Cd: Cadmium; CDF: Cation diffusion facilitator; Chl: Chlorophyll; CTR: Cu TRansporter families; DAGs: Directed acyclic graphs; DEGs: Differentially expressed genes; DVR: Divinyl chlorophyllide, an 8-vinyl-reductase; FPN: FerroportinN; FTIR: Fourier transform infrared; FTR: Fe TRansporter; GO: Gene Ontology; IC50: Growth half maximal inhibitory concentration; ICP: Inductively coupled plasma; MF: molecular function; NRAMPs: Natural resistance-associated aacrophage proteins; OD: Optical density; RPKM: Reads Per Kilobase of Exon Per Million Reads Mapped; VIT1: Vacuolar iron transporter 1 families; ZIPs: Zrt-, Irt-like proteins.

Synergistic effect of pyrene and heavy metals (Zn, Pb, and Cd) on phytoremediation potential of Medicago sativa L. (alfalfa) in multi-contaminated soil

The environment in India is contaminated with polycyclic aromatic hydrocarbons (PAHs) due to the occurrence of large anthropogenic activities, i.e., fuel combustion, mineral roasting, and biomass burning. Hence, 13 toxic PAHs were detected: phenanthrene, anthracene, fluoranthene, pyrene, and benz(a) anthracene, ben-zo; (b) fluoranthene, benzo(k) fluoranthene, benzo(a) pyrene, benzo(ghi)perylene, dibenz (ah) anthracene, indeno1,2,3-(cd) pyrene, coronene and coronene in the environment (i.e., ambient particulate matter, road dust, sludge, and sewage) of the most industrialized area. Pollutants such as heavy metals and polycyclic aromatic hydrocarbons co-contaminate the soil and pose a significant hazard to the ecosystem because these pollutants are harmful to both humans and the environment. Phytoremediation is an economical plant-based natural approach for soil clean-up that has no negative impact on ecosystems. The aim of this study was to investigate the effects of pyrene (500 mg kg-1), Zn (150 mg kg-1), Pb (150 mg kg-1), and Cd (150 mg kg-1) alone and in combination on the phytoextraction efficiency of Medicago sativa growing in contaminated soil. Plant biomass, biochemical activities, translocation factors, accumulation of heavy metals, and pyrene removal were determined. After 60 days of planting, compared with those of the control plants, the growth parameters, biomass, and chlorophyll content of the M. sativa plants were significantly lower, and the reactive oxygen species activity, such as proline and polyphenol content and metallothionein protein content, was markedly greater in the pyrene and heavy metal-polluted soils. Furthermore, the combined toxicity of pyrene and all three metals on M. sativa growth and biochemical parameters was significantly greater than that of pyrene, Zn, Pb, or Cd alone, indicating the synergistic effect of pyrene and heavy metals on cytotoxicity. Pyrene stress increased Cd accumulation in M. sativa. After pyrene exposure alone or in combination with Zn-pyrene, a greater pyrene removal rate (85.5-81.44%) was observed than that in Pb-pyrene, Cd-pyrene, and Zn-Pb-Cd-pyrene polluted soils (62.78-71.27%), indicating that zinc can enhance the removal of pyrene from contaminated soil. The resulting hypotheses demonstrated that Medicago sativa can be used as a promising phytoremediation agent for co-contaminated soil.

Synergistic remediation of phenanthrene-cadmium co-contaminants by an immobilized acclimated bacterial-fungal consortium and its community response

Bioremediation has tremendous potential to mitigate the serious threats posed by polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs). In the present study, nine bacterial-fungal consortia were progressively acclimated under different culture conditions. Among them, a microbial consortium 1, originating from activated sludge and copper mine sludge microorganisms, was developed through the acclimation of a multi-substrate intermediate (catechol)-target contaminant (Cd²⁺, phenanthrene (PHE)). Consortium 1 exhibited the best PHE degradation, with an efficiency of 95.6% after 7 d of inoculation, and its tolerance concentration for Cd²⁺ was up to 1800 mg/L within 48 h. Bacteria Pandoraea and Burkholderia-Caballeronia-Paraburkholderia, as well as fungi Ascomycota and Basidiomycota predominated in the consortium 1. Furthermore, a biochar-loaded consortium was constructed to better cope with the co-contamination behavior, which exhibited excellent adaptation to Cd²⁺ ranging of 50-200 mg/L. Immobilized consortium efficiently degraded 92.02-97.77% of 50 mg/L PHE within 7 d while removing 93.67-99.04% of Cd²⁺. In remediation of co-pollution, immobilization technology improved the bioavailability of PHE and dehydrogenase activity of the consortium to enhance PHE degradation, and the phthalic acid pathway was the main metabolic pathway. As for Cd²⁺ removal, oxygen-containing functional groups (-OH, C=O, and C-O) of biochar or microbial cell walls and EPS components, fulvic acid and aromatic proteins, participated through chemical complexation and precipitation. Furthermore, immobilization led to more active consortium metabolic activity during the reaction, and the community structure developed in a more favorable direction. The dominant species were Proteobacteria, Bacteroidota, and Fusarium, and the predictive expression of functional genes corresponding to key enzymes was elevated. This study provides a basis for combining biochar and acclimated bacterial-fungal consortia for co-contaminated site remediation.

Impact of environmental microplastics alone and mixed with benzo[a]pyrene on cellular and molecular responses of Mytilus galloprovincialis

The hazard of microplastic (MP) pollution in marine environments is a current concern. However, the effects of environmental microplastics combined with other pollutants are still poorly investigated. Herein, impact of ecologically relevant concentrations of environmental MP alone (50 µg/L) or combined with B[a]P (1 µg/L) was assessed in mussel Mytilus galloprovincialis after a short-term exposure (1 and 3 days) to environmental MP collected from a north-Mediterranean beach. Raman Microspectroscopy (RMS) revealed bioaccumulation in mussel hemolymph of MP, characterized by polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), polyethylene vinyl acetate (PEVA) and high-density polyethylene (HDPE), with abundance of MP sized 1.22-0.45 µm. An increase of B[a]P was detected in mussels after 3-day exposure, particularly when mixed with MP. Both contaminants induced cytotoxic and genotoxic effects on hemocytes as determined by lysosomal membrane stability (LMS), micronuclei frequency (FMN), and DNA fragmentation rate by terminal dUTP nick-end labeling (TUNEL). About apoptosis/DNA repair processes, P53 and DNA-ligase increased at 1-day exposure in all conditions, whereas after 3 days increase of bax, Cas-3 and P53 and decrease of Bcl-2 and DNA-ligase were revealed, suggesting a shift towards a cell apoptotic event in exposed mussels. Overall, this study provides new insights on the risk of MP for the marine ecosystem, their ability to accumulate xenobiotics and transfer them to marine biota, with potential adverse repercussion on their health status.

Impact of benzo[a]pyrene with other pollutants induce the molecular alternation in the biological system: Existence, detection, and remediation methods

The exposure of benzo [a]pyrene (BaP) in recent times is rather unavoidable than ever before. BaP emissions are sourced majorly from anthropogenic rather than natural provenance from wildfires and volcanic eruptions. A major under-looked source is via the consumption of foods that are deep-fried, grilled, and charcoal smoked foods (meats in particular). BaP being a component of poly aromatic hydrocarbons has been classified as a Group I carcinogenic agent, which has been shown to cause both systemic and localized effects in animal models as well as in humans; has been known to cause various forms of cancer, accelerate neurological disorders, invoke DNA and cellular damage due to the generation of reactive oxygen species and involve in multi-generational phenotypic and genotypic defects. BaP's short and accumulated exposure has been shown in disrupting the fertility of gamete cells. In this review, we have discussed an in-depth and capacious run-through of the various origins of BaP, its economic distribution and its impact as well as toxicological effects on the environment and human health. It also deals with a mechanism as a single compound and its ability to synergize with other chemicals/materials, novel sensitive detection methods, and remediation approaches held in the environment.

Development of an ecotoxicological test procedure for soil microalgae

Since the 80s, ISO and OECD organizations have been developing guidelines for assessing the toxicity of new and existing chemical substances to soil biota. Up to now, any of these guidelines had soil algae as test organisms. Nevertheless, microalgae are relevant components of soil microbial communities and soil biological crusts (BSC) with a great contribution to different soil functions and ecosystem services. In an attempt to bridge the gap, the present work aimed to develop, describe and validate a standard operating procedure for an ecotoxicological test with soil microalgae. Three phases were performed, each one with specific objectives. First, soil microalgae and cyanobacteria were isolated from BSC and then genetically and morphologically characterized. The green microalga Micractinium inermum was selected because it is a species with a wide geographic distribution. Secondly, M. inermum growth curves were obtained in liquid (BG₁₁ and Woods-Hole MBL) and solid media (OECD artificial soil) to determine test duration. The growth curves were also used to analyze the reproducibility of the test's endpoint and to propose a validation criterion. Ultimately, a range of concentrations of two reference substances (glyphosate and copper) were tested, both in soil and liquid media, to assess procedure's reproducibility. The tests made in liquid medium followed the standard guideline for ecotoxicological tests with freshwater microalgae and cyanobacteria (OECD 201:2011). The results obtained prove that when the artificial soil is used, as a test substrate, the sensitivity of M. inermum increases. The tests performed with both reference substances demonstrate that the procedure described for testing in soil was reproducible. Additionally, it will be relevant to test with other reference substances and adjust the procedure for natural soils. It will be also interesting to validate the test procedure with soil cyanobacteria.

Copper stimulates neonicotinoid insecticide thiacloprid degradation by Ensifer adhaerens TMX-23

AIMS

Aims of this study are to elucidate the molecular mechanism of copper-improved thiacloprid (THI) degradation by Ensifer adhaerens TMX-23 and characterize copper resistance of this strain.

METHODS AND RESULTS

Resting cells of E. adhaerens TMX-23 were used to degrade THI, with formation of THI amide and 98·31% of 0·59 mmol l^-1 THI was degraded in 100 min. The addition of copper improved the degradation of THI and showed little inhibitory effects on the growth of E. adhaerens TMX-23. E. adhaerens TMX-23 degraded THI to THI amide by nitrile hydratases (NhcA and NhpA). QPCR analysis indicated that the expression of nhpA was up-regulated in the presence of copper. E. adhaerens TMX-23 nitrile hydratases were purified, and enzyme assay of NhpA exhibited the highest NHase activity toward THI. The addition of copper activated the activity of NhcA. Soil degradation experiment indicated that E. adhaerens TMX-23 could quickly eliminate THI residual in copper-added soil.

CONCLUSIONS

Copper improved THI degradation by E. adhaerens TMX-23 was attributed to the induced expression of nhpA and activated NhcA.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study broadens the investigation of regulatory mechanism of NHase expression and provided theoretical basis for using metal-resistant microbes to degrade pesticide in heavy metal co-contaminated environments.

Acid-adapted microalgae exhibit phenotypic changes for their survival in acid mine drainage samples

Phenotypic plasticity or genetic adaptation in an organism provides phenotypic changes when exposed to the extreme environmental conditions. The resultant physiological and metabolic changes greatly enhance the organism's potential for its survival in such harsh environments. In the present novel approach, we tested the hypothesis whether acid-adapted microalgae, initially isolated from non-acidophilic environments, can survive and grow in acid-mine-drainage (AMD) samples. Two acid-adapted microalgal strains, Desmodesmus sp. MAS1 and Heterochlorella sp. MAS3, were tested individually or in combination (co-culture) for phenotypic changes during their growth in samples collected from AMD. The acid-adapted microalgae in AMD exhibited a two-fold increase in growth when compared with those grown at pH 3.5 in BBM up to 48 h and then declined. Furthermore, oxidative stress triggered several alterations such as increased cell size, granularity, and enhanced lipid accumulation in AMD-grown microalgae. Especially, the apparent limitation of phosphate in AMD inhibited the uptake of copper and iron in the cultures. Interestingly, growth of the acid-adapted microalgae in AMD downregulated amino acid metabolic pathways as a survival mechanism. This study demonstrates for the first time that acid-adapted microalgae can survive under extreme environmental conditions as exist in AMD by effecting significant phenotypic changes.

The pathways by which the marine diatom Thalassiosira sp. OUC2 biodegrades p-xylene, combined with a mechanistic analysis at the proteomic level

A marine diatom, Thalassiosira sp. OUC2, was isolated from natural seawater collected from Daya Bay, China. This diatom degraded 1.25-40 mg L^-1p-xylene within five days, at a removal efficiency exceeding 98%. Gas chromatography-mass spectrometer (GC-MS) analysis indicated that p-xylene was converted into 4-methylbenzyl alcohol, p-toluic acid, and p-cresol in the presence of strain OUC2. Meanwhile, proteomic analysis showed that, after exposure to p-xylene, several algal enzymes were significantly upregulated: including monooxygenase, alcohol dehydrogenase, benzaldehyde dehydrogenase, benzoate 1,2-dioxygenase, and catechol 2,3-dioxygenase. Moreover, ecotoxicological tests suggested that the intermediate metabolites were less toxic than the parent compound (p-xylene). Thalassiosira sp. OUC2 may thus be suitable for the remediation of p-xylene-contaminated marine environments.

Characterization of the Phenanthrene-Degrading Sphingobium yanoikuyae SJTF8 in Heavy Metal Co-Existing Liquid Medium and Analysis of Its Metabolic Pathway

Polycyclic aromatic hydrocarbons (PAHs) are common organic pollutants with great carcinogenic threaten, and metal/PAH-contaminated environments represent one of the most difficult remedial challenges. In this work, Sphingobium yanoikuyae SJTF8 was isolated and identified with great and stable PAH-degrading efficiency even under stress conditions. It could utilize typical PAHs (naphthalene, phenanthrene, and anthracene) and heterocyclic and halogenated aromatic compounds (dibenzothiophene and 9-bromophenanthrene) as the sole carbon source. It could degrade over 98% of 500 mg/L phenanthrene in 4 days, and the cis-3,4-dihydrophenanthrene-3,4-diol was the first-step intermediate. Notably, strain SJTF8 showed great tolerance to heavy metals and acidic pH. Supplements of 0.30 mM of Cu2+, 1.15 mM of Zn2+, and 0.01 mM of Cd2+ had little effect on its cell growth and phenanthrene degradation; phenanthrene of 250 mg/L could still be degraded completely in 48 h. Further, the whole genome sequence of S. yanoikuyae SJTF8 was obtained, and three plasmids were found. The potential genes participating in stress-tolerance and PAH-degradation were annotated and were found mostly distributed in plasmids 1 and 2. Elimination of plasmid 2 resulted in the loss of the PAH-degradation ability. On the basis of genome mining results, the possible degrading pathway and the metabolites of S. yanoikuyae SJTF8 to phenanthrene were predicted.

Trophic transfer affects cytogenetic and antioxidant responses of the mussel Mytilus galloprovincialis to copper and benzo(α)pyrene

The impacts of environmental pollutants on marine organisms can be determined by the routes of exposure. Various routes of exposure, including dietary exposure and waterborne exposure with or without feeding, were applied to study the cytogenetic responses in marine mussels Mytilus galloprovincials to typical pollutants, BaP (53.74 ± 19.79 μg/L) and Cu (47.38 ± 3.10 μg/L). The increased DNA strand breaks and micronucleus formation were found in haemocytes of mussels via the dietary exposure, indicating the vital role of trophic transfer in toxicity induction. The deeper exploration to relate BaP induced cytogenetic alterations with key antioxidant defense factors, SOD and GST, was performed under different exposure routes. The results revealed the significantly inhibited SOD activity via the trophic transfer, suggesting more direct or prompt role of SOD in antioxidant defense. On contrary, gene expressions of both sod and gst were up-regulated upon all routes of exposures, and showed negative correlation with enzyme activities. The results suggested the asynchronous regulation of studied antioxidant factors at transcriptional and enzyme functional level in mussels upon the change of exposure routes. The study brings out the first observation of trophic transfer influenced cytogenetic and antioxidant responses to pollutants and their alterative risk to marine organisms.

Nickel uptake and distribution in Agropyron cristatum L. in the presence of pyrene

PAHs affect the uptake of heavy metal by plants. The uptake pathway, distribution and detoxification of nickel (Ni) in Agropyron cristatum L. (A. cristatum) were investigated in the presence of pyrene in this study. Most of Ni was adsorbed on the cell wall in the insoluble phosphate (57.31-72.18%) form and pectate and protein integrated (38.27-38.98%) form. Ni was transferred to the organelle (from 37.84% to 40.52%) in the presence of pyrene. The concentration of Ni in A. cristatum decreased by 27.42%; it was affected by the ATP production inhibitor and 29.49% by the P-type ATPase inhibitor. The results indicated that the uptake of Ni related closely to the synthesis and decomposition of ATP and was an active uptake process. Contents of phytochelatins (PCs) in A. cristatum in Ni contaminated soils increased by 19.97%, and an additional 4.13% increase occurred in the presence of pyrene when compared to single Ni contamination. The content of malic acid in A. cristatum was the highest for 262.78 mg g^-1 in shoots and 46.81 mg g^-1 in roots with Ni contamination. Besides, acetic acid in shoots and roots increased by 40.25% and 102.63% with Ni contamination, and by 61.59% and 185.71% with Ni-pyrene co-contamination. This study preliminarily explored the inhibitory mechanism of pyrene on plant uptake of Ni.

Acid-tolerant microalgae can withstand higher concentrations of invasive cadmium and produce sustainable biomass and biodiesel at pH 3.5

Two acid-tolerant microalgae, Desmodesmus sp. MAS1 and Heterochlorella sp. MAS3, originally isolated from non-acidophilic environment, were tested for their ability to withstand higher concentrations of an invasive heavy metal, cadmium (Cd), at an acidic pH of 3.5 and produce biomass rich in biodiesel. The growth analysis, in terms of chlorophyll, revealed that strain MAS1 was tolerant even to 20 mg L^-1 of Cd while strain MAS3 could withstand only up to 5 mg L^-1. When grown in the presence of 2 mg L^-1, a concentration which is 400-fold higher than that usually occurs in the environment, the microalgal strains accumulated >58% of Cd from culture medium at pH 3.5. FTIR analysis of Cd-laden biomass indicated production of significant amounts of biodiesel rich in fatty acid esters. This is the first study that demonstrates the capability of acid-tolerant microalgae to grow well and remove Cd at acidic pH.

Low molecular weight organic acids enhance the high molecular weight polycyclic aromatic hydrocarbons degradation by bacteria

The biodegradation potential of three bacterial cultures isolated from the rhizosphere of maize (Zea mays) and Sudan grass (Sorghum sudanense) grown in PAHs contaminated soils to degrade benzo[a]pyrene (BaP) and pyrene (PYR) was assessed. Of the three bacterial cultures isolated, two belonged to Gram-positive bacteria of phylum Actinobacteria namely Arthrobacter sp. MAL3 and Microbacterium sp. MAL2. The Gram-negative bacterial culture was Stenotrophomonas sp. MAL1, from the phylum Proteobacteria. The cultures were grown in the presence of BaP and PYR as sole carbon sources and with the addition of low molecular weight organic acids (LMWOAs) mixture. After 10-14 days of exposure, all the bacterial isolates exhibited a complete degradation of PYR with the addition of LMWOAs mixture, whereas only 38.7% of BaP was degraded by Stenotrophomonas sp. MAL1 with the addition of LMWOAs mixture. In addition, enhanced PAHs biodegradation by bacterial culture was observed when the PAHs present as mixture (BaP + PYR) with the addition of LMWOAs. Dioxygenase genes were detected in Stenotrophomonas sp. MAL1 (phnAC), and Arthrobacter sp. MAL3 (nidA and PAH-RHDα). Therefore, this study provides new insights on the influence of LMWOAs in enhancing the degradation of high molecular weight (HMW) PAHs in soil by rhizosphere bacterial cultures.

Advances in the technologies for studying consortia of bacteria and cyanobacteria/microalgae in wastewaters

The excessive generation and discharge of wastewaters have been serious concerns worldwide in the recent past. From an environmental friendly perspective, bacteria, cyanobacteria and microalgae, and the consortia have been largely considered for biological treatment of wastewaters. For efficient use of bacteria‒cyanobacteria/microalgae consortia in wastewater treatment, detailed knowledge on their structure, behavior and interaction is essential. In this direction, specific analytical tools and techniques play a significant role in studying these consortia. This review presents a critical perspective on physical, biochemical and molecular techniques such as microscopy, flow cytometry with cell sorting, nanoSIMS and omics approaches used for systematic investigations of the structure and function, particularly nutrient removal potential of bacteria‒cyanobacteria/microalgae consortia. In particular, the use of specific molecular techniques of genomics, transcriptomics, proteomics metabolomics and genetic engineering to develop more stable consortia of bacteria and cyanobacteria/microalgae with their improved biotechnological capabilities in wastewater treatment has been highlighted.

Potential of acid-tolerant microalgae, Desmodesmus sp. MAS1 and Heterochlorella sp. MAS3, in heavy metal removal and biodiesel production at acidic pH

Metals in traces are vital for microalgae but their occurrence at high concentrations in habitats is a serious ecological concern. We investigated the potential of two acid-tolerant microalgae, Desmodesmus sp. MAS1 and Heterochlorella sp. MAS3, isolated from neutral environments, for simultaneous removal of heavy metals such as copper (Cu), iron (Fe), manganese (Mn) and zinc (Zn), and production of biodiesel when grown at pH 3.5. Excepting Cu, the selected metals at concentrations of 10-20 mg L^-1 supported good growth of both the strains. Cellular analysis for metal removal revealed the predominance of intracellular mechanism in both the strains resulting in 40-80 and 40-60% removal of Fe and Mn, respectively. In-situ transesterification of biomass indicated enhanced biodiesel yield with increasing concentrations of metals suggesting that both these acid-tolerant microalgae may be the suitable candidates for simultaneous remediation, and sustainable biomass and biodiesel production in environments like metal-rich acid mine drainages.

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

Remediation of soil contaminated with pollutants using biological agents is more a sustainable and greener approach as compared to physico-chemical technologies. We recently confirmed that a microalga, Chlorella sp. MM3, and a bacterium, Rhodococcus wratislaviensis strain 9, can degrade high-molecular weight PAHs. In this study, an algal-bacterial system of these two strains was developed by long-term growth on a mixture of phenanthrene, pyrene, and benzo[a]pyrene (BaP). In a soil spiked with 50 mg L^-1 phenanthrene, 10 mg L^-1 of pyrene and 10 mg L^-1 of BaP, the algal-bacterial system degraded these PAHs almost completely in slurry phase within 30 days. Also, the algal-bacterial system was able to successfully remediate these three PAHs in a soil long-term contaminated with 245.1 mg kg^-1 of 16 PAHs and several heavy metals under slurry phase in 21 days. Use of such appropriate assays as chlorophyll estimation for the microalga and semi-quantitative PCR for the bacterium confirmed survival of both the strains during soil bioremediation. Moreover, the residual toxicity test involving Escherichia coli DH5α that expresses green fluorescent protein indicated the successful bioremediation of PAHs-contaminated soil in slurry phase. For the first time, here we demonstrate the great potential of an algal-bacterial synergy in bioremediation of soil long-term contaminated with PAHs even in the presence of toxic heavy metals.

Biodegradation of high-molecular weight PAHs by Rhodococcus wratislaviensis strain 9: Overexpression of amidohydrolase induced by pyrene and BaP

A Gram-positive bacterium, Rhodococcus wratislaviensis strain 9, completely degraded 280 μM of phenanthrene, 40% of 50 μM pyrene or 28% of 40 μM benzo[a]pyrene (BaP), each supplemented in M9 medium, within 7 days. PCR screening with gene-specific primers indicated that the strain 9 harbors genes which code for 2,3-dihydroxybiphenyl 1,2-dioxygenase (bphC), 4-nitrophenol 2-monooxygenase component B (npcB) as well as oxygenase component (nphA1), 4-hydroxybenzoate 3-monooxygenase (phbH), extradiol dioxygenase (edo), and naphthalene dioxygenase (ndo), all of which are largely implicated in biodegradation of several aromatic hydrocarbons. An orthogonal design experiment revealed that BaP biodegradation was greatly enhanced by surfactants such as Tween 80, Triton X-100 and linoleic acid, suggesting that bioavailability is the major limiting factor in bacterial metabolism of BaP. Both pyrene and BaP induced the overexpression of amidohydrolase, a metallo-dependent hydrolase, possibly involved in their biodegradation by strain 9. The up-regulation of amidohydrolase gene induced by BaP, in particular, was also confirmed by semi-quantitative RT-PCR. Catechol 2,3-dioxygenase and the large subunit of ndo, but not amidohydrolase, accumulated when the strain 9 was grown on phenanthrene. To our knowledge, this is the first report on overexpression of amidohydrolase and its possible implication in bacterial degradation of high-molecular weight PAHs.

Metabolomics reveals defensive mechanisms adapted by maize on exposure to high molecular weight polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons are an important group of persistent organic pollutants. Using plants to remediate PAHs has been recognized as a cost-effective and environmentally friendly technique. However, the overall impact of PAHs on the regulation of plant metabolism has not yet been explored. In this study, we analyzed the alteration in the maize (Zea mays L.) metabolome on exposure to high molecular weight PAHs such as benzo[a]pyrene (BaP) and pyrene (PYR) in a hydroponic medium, individually and as a mixture (BaP + PYR) using GC-MS. The differences in the metabolites were analyzed using XCMS (an acronym for various forms (X) of chromatography-mass spectrometry), an online-based data analysis tool. A significant variation in metabolites was observed between treatment groups and the unspiked control group. The univariate, multivariate and pathway impact analysis showed there were more significant alterations in metabolic profiles between individual PAHs and the mixture of BaP and PYR. The marked changes in the metabolites of galactose metabolism and aminoacyl tRNA biosynthesis in PAHs treated maize leaves exhibit the adaptive defensive mechanisms for individual and PAHs mixture. Therefore, the metabolomics approach is essential for an understanding of the complex biochemical responses of plants to PAHs contaminants. This knowledge will shed new light in the field of phytoremediation, bio-monitoring, and environmental risk assessment.

Consortia of cyanobacteria/microalgae and bacteria in desert soils: an underexplored microbiota

Desert ecosystem is generally considered as a lifeless habitat with extreme environmental conditions although it is colonized by extremophilic microorganisms. Cyanobacteria, microalgae, and bacteria in these habitats could tolerate harsh and rapidly fluctuating environmental conditions, intense ultraviolet radiation, and lack of water, leading to cell desiccation. They possess valuable metabolites withstanding extreme environmental conditions and make them good candidates for industrial applications. Moreover, most natural microorganisms in these extreme habitats exist as consortia that provide robustness and extensive metabolic capabilities enabling them to establish important relationships in desert environments. Engineering of such consortia of cyanobacteria, microalgae, and bacteria would be functional in the sustainable development of deserts through improving soil fertility, water preservation, primary production, pollutant removal, and maintaining soil stability. Modern tools and techniques would help in constructing highly functional cyanobacterial/microalgal-bacterial consortia that are greatly useful in the establishment of vegetation in deserts as well as in biotechnological applications.

Influence of a mixture of metals on PAHs biodegradation processes in soils

In order to assess the effect of mixed pollutants, the influence of different concentration levels of a mixture of metals (Cr, Co, Pb, Mn, Ni, Cu, Zn) on the biodegradation of some PAHs (phenanthrene, fluoranthene, pyrene, benzo[b]fluoranthene and benzo[a]pyrene) in soil samples was evaluated. To do so, groups of microcosms of a natural soil from the region of Sabadell (Barcelona, Spain) were prepared as a reproduction of the native environment at laboratory scale, under controlled conditions. Mixtures of PAHs and metals were carefully selected, according to soil characterization and microbiological growth preliminary assays, and were added to microcosms. These microcosms were analyzed at various times, along two months, to obtain PAHs dissipation time-courses. A first-order kinetic modelling allowed obtaining different rate constants and DT50 values as a function of the metal levels introduced in microcosms. As a general observation, the higher the concentration of metals, the lower the biodegradation of PAHs of 3-4 rings (phenanthrene, fluoranthene and pyrene). On the other hand, no important effect on the biodegradation of higher molecular weight PAHs (benzo[b]fluoranthene and benzo[a]pyrene) was observed at the different concentration levels of metals tested.

Kinetics of PAH degradation by a new acid-metal-tolerant Trabulsiella isolated from the MGP site soil and identification of its potential to fix nitrogen and solubilize phosphorous

Development of an efficient bioinoculum is considered as an appropriate remedial approach to treat the PAHs-metal mixed contaminated sites. Therefore, we aimed to isolate a degrader able to exert an outstanding PAH catabolic potential with added traits of pH-metal-resistance, N-fix or P-solubilization from a manufactured gas plant site soil. The identified strain (MTS-6) was a first low and high molecular weight (LMW and HMW) PAHs degrading Trabulsiella sp. tolerant to pH 5. MTS-6 completely degraded the model 3 [150mgL(-1) phenanthrene (Phe)], 4 [150mgL(-1) pyrene (Pyr)] and 5 [50mgL(-1) benzo[a]pyrene (BaP)] ring PAHs in 6, 25 and 90 days, respectively. Presence of co-substrate (100mgL(-1) Phe) increased the biodegradation rate constant (k) and decreased the half-life time (t1/2) of HMW PAHs (100mgL(-1) Pyr or 50mgL(-1) BaP). The strain fixed 47μgmL(-1)N and solubilized 58μgmL(-1)P during PAH metabolism and exhibited an EC50 value of 3-4mgL(-1) for Cu, Cd, Pb and Zn. Over 6mgL(-1) metal levels was lethal for the microbe. The identified bacterium (MTS-6) with exceptional multi-functional traits opens the way for its exploitation in the bioremediation of manufactured gas plant sites in a sustainable way by employing bioaugmentation strategy.