From organic pollutants to bioplastics: insights into the bioremediation of aromatic compounds by Cupriavidus necator

Natural Chromosome-Chromid Fusion across rRNA Operons in a Burkholderiaceae Bacterium

Chromids (secondary chromosomes) in bacterial genomes that are present in addition to the main chromosome appear to be evolutionarily conserved in some specific bacterial groups. In rare cases among these groups, a small number of strains from Rhizobiales and Vibrionales were shown to possess a naturally fused single chromosome that was reported to have been generated through intragenomic homologous recombination between repeated sequences on the chromosome and chromid. Similar examples have never been reported in the family Burkholderiaceae, a well-documented group that conserves chromids. Here, an in-depth genomic characterization was performed on a Burkholderiaceae bacterium that was isolated from a soil bacterial consortium maintained on diesel fuel and mutagenic benzo[a]pyrene. This organism, Cupriavidus necator strain KK10, was revealed to carry a single chromosome with unexpectedly large size (>6.6 Mb), and results of comparative genomics with the genome of C. necator N-1T indicated that the single chromosome of KK10 was generated through fusion of the prototypical chromosome and chromid at the rRNA operons. This fusion hypothetically occurred through homologous recombination with a crossover between repeated rRNA operons on the chromosome and chromid. Some metabolic functions that were likely expressed from genes on the prototypical chromid region were indicated to be retained. If this phenomenon-the bacterial chromosome-chromid fusion across the rRNA operons through homologous recombination-occurs universally in prokaryotes, the multiple rRNA operons in bacterial genomes may not only contribute to the robustness of ribosome function, but also provide more opportunities for genomic rearrangements through frequent recombination. IMPORTANCE A bacterial chromosome that was naturally fused with the secondary chromosome, or "chromid," and presented as an unexpectedly large single replicon was discovered in the genome of Cupriavidus necator strain KK10, a biotechnologically useful member of the family Burkholderiaceae. Although Burkholderiaceae is a well-documented group that conserves chromids in their genomes, this chromosomal fusion event has not been previously reported for this family. This fusion has hypothetically occurred through intragenomic homologous recombination between repeated rRNA operons and, if so, provides novel insight into the potential of multiple rRNA operons in bacterial genomes to lead to chromosome-chromid fusion. The harsh conditions under which strain KK10 was maintained-a genotoxic hydrocarbon-enriched milieu-may have provided this genotype with a niche in which to survive.

Two-Stage Polyhydroxyalkanoates (PHA) Production from Cheese Whey Using Acetobacter pasteurianus C1 and Bacillus sp. CYR1

Cheese whey (CW) can be an excellent carbon source for polyhydroxyalkanoates (PHA)-producing bacteria. Most studies have used CW, which contains high amounts of lactose, however, there are no reports using raw CW, which has a relatively low amount of lactose. Therefore, in the present study, PHA production was evaluated in a two-stage process using the CW that contains low amounts of lactose. In first stage, the carbon source existing in CW was converted into acetic acid using the bacteria, Acetobacter pasteurianus C1, which was isolated from food waste. In the second stage, acetic acid produced in the first stage was converted into PHA using the bacteria, Bacillus sp. CYR-1. Under the condition of without the pretreatment of CW, acetic acid produced from CW was diluted at different folds and used for the production of PHA. Strain CYR-1 incubated with 10-fold diluted CW containing 5.7 g/L of acetic acid showed the higher PHA production (240.6 mg/L), whereas strain CYR-1 incubated with four-fold diluted CW containing 12.3 g/L of acetic acid showed 126 mg/L of PHA. After removing the excess protein present in CW, PHA production was further enhanced by 3.26 times (411 mg/L) at a four-fold dilution containing 11.3 g/L of acetic acid. Based on Fourier transform infrared spectroscopy (FT-IR), and ¹H and ¹³C nuclear magnetic resonance (NMR) analyses, it was confirmed that the PHA produced from the two-stage process is poly-β-hydroxybutyrate (PHB). All bands appearing in the FT-IR spectrum and the chemical shifts of NMR nearly matched with those of standard PHB. Based on these studies, we concluded that a two-stage process using Acetobacter pasteurianus C1 and Bacillus sp. CYR-1 would be applicable for the production of PHB using CW containing a low amount of lactose.

Metagenomic Analysis Reveals Bacterial and Fungal Diversity and Their Bioremediation Potential From Sediments of River Ganga and Yamuna in India

In this study, we report the presence of a microbial community of bioremediation potential in terms of relative abundance and taxonomic biodiversity in sediment samples of river Ganga and Yamuna, India at nine different sites. Metagenomic libraries were constructed using TruSeq Nano DNA Library Prep Kit and sequenced on NextSeq 500 by Illumina Next Generation Sequencing (NGS) technology. Bioremediation bacteria belong to 45 genera with 92 species and fungi belong to 13 genera with 24 species have been classified using Kaiju taxonomical classification. The study revealed that Proteobacteria was the most dominant bacterial flora, followed by Actinobacteria, Firmicutes, and Deinococcus-Thermus. PCA analysis revealed that bioremediation bacteria viz. Streptomyces bikiniensis, Rhodococcus qingshengii, Bacillus aerophilus, Pseudomonas veronii, etc., were more dominant in highly polluted river stretch as compared to less polluted river stretch. Similarly, the relative abundance of bioremediation fungi viz. Phanerochaete chrysosporium and Rhizopus oryzae, etc., were significantly correlated with the polluted Kanpur stretch of river Ganga. Several protein domains, which play a pivotal role in bioremediation in the polluted environments, including urea ABC transporter, UrtA, UrtD, UrtE, zinc/cadmium/mercury/lead-transporting ATPase, etc., were identified using protein domain analysis. The protein domains involved in pesticide biodegradation viz. P450, short-chain dehydrogenases/reductases (SDR), etc., were also discovered in river sediment metagenomics data. This is the first report on the richness of bioremediation microbial communities in the Ganga and Yamuna riverine ecosystems, highlighting their importance in aquatic pollution management.

Fed-batch polyhydroxybutyrate production by Paraburkholderia sacchari from a ternary mixture of glucose, xylose and arabinose

Polyhydroxybutyrate (PHB) is a biodegradable bioplastic that is comparable with many petroleum-based plastics in terms of mechanical properties and is highly biocompatible. Lignocellulosic biomass conversion into PHB can increase profit and add sustainability. Glucose, xylose and arabinose are the main monomer sugars derived from upstream lignocellulosic biomass processing. The sugar mixture ratios may vary greatly depending on the pretreatment and enzymatic hydrolysis conditions. Paraburkholderia sacchari DSM 17165 is a bacterium strain that can convert all three sugars into PHB. In this study, fed-batch mode was applied to produce PHB on three sugar mixtures (glucose:xylose:arabinose = 4:2:1, 2:2:1, 1:2:1). The highest PHB concentration produced was 67 g/L for 4:2:1 mixture at 41 h corresponding to an accumulation of 77% of cell dry weight as PHB. Corresponding sugar conversion efficiency and productivity were 0.33 g PHB/g sugar consumed and 1.6 g/L/h, respectively. The results provide references for process control to maximize PHB production from real sugar streams derived from corn fibre.

The Transcriptomic Landscape of Cupriavidus metallidurans CH34 Acutely Exposed to Copper

Bacteria are increasingly used for biotechnological applications such as bioremediation, biorecovery, bioproduction, and biosensing. The development of strains suited for such applications requires a thorough understanding of their behavior, with a key role for their transcriptomic landscape. We present a thorough analysis of the transcriptome of Cupriavidus metallidurans CH34 cells acutely exposed to copper by tagRNA-sequencing. C. metallidurans CH34 is a model organism for metal resistance, and its potential as a biosensor and candidate for metal bioremediation has been demonstrated in multiple studies. Several metabolic pathways were impacted by Cu exposure, and a broad spectrum of metal resistance mechanisms, not limited to copper-specific clusters, was overexpressed. In addition, several gene clusters involved in the oxidative stress response and the cysteine-sulfur metabolism were induced. In total, 7500 transcription start sites (TSSs) were annotated and classified with respect to their location relative to coding sequences (CDSs). Predicted TSSs were used to re-annotate 182 CDSs. The TSSs of 2422 CDSs were detected, and consensus promotor logos were derived. Interestingly, many leaderless messenger RNAs (mRNAs) were found. In addition, many mRNAs were transcribed from multiple alternative TSSs. We observed pervasive intragenic TSSs both in sense and antisense to CDSs. Antisense transcripts were enriched near the 5' end of mRNAs, indicating a functional role in post-transcriptional regulation. In total, 578 TSSs were detected in intergenic regions, of which 35 were identified as putative small regulatory RNAs. Finally, we provide a detailed analysis of the main copper resistance clusters in CH34, which include many intragenic and antisense transcripts. These results clearly highlight the ubiquity of noncoding transcripts in the CH34 transcriptome, many of which are putatively involved in the regulation of metal resistance.

Applying Statistical Design of Experiments To Understanding the Effect of Growth Medium Components on Cupriavidus necator H16 Growth

Chemically defined media (CDM) for cultivation of C. necator vary in components and compositions. This lack of consensus makes it difficult to optimize new processes for the bacterium. This study employed statistical design of experiments (DOE) to understand how basic components of defined media affect C. necator growth. Our growth model predicts that C. necator can be cultivated to high cell density with components held at low concentrations, arguing that CDM for large-scale cultivation of the bacterium for industrial purposes will be economically competitive. Although existing CDM for the bacterium are without amino acids, addition of a few amino acids to growth medium shortened lag phase of growth. The interactions highlighted by our growth model show how factors can interact with each other during a process to positively or negatively affect process output. This approach is efficient, relying on few well-structured experimental runs to gain maximum information on a biological process, growth.

Cupriavidus necator H16 is gaining significant attention as a microbial chassis for range of biotechnological applications. While the bacterium is a major producer of bioplastics, its lithoautotrophic and versatile metabolic capabilities make the bacterium a promising microbial chassis for biofuels and chemicals using renewable resources. It remains necessary to develop appropriate experimental resources to permit controlled bioengineering and system optimization of this microbe. In this study, we employed statistical design of experiments to gain understanding of the impact of components of defined media on C. necator growth and built a model that can predict the bacterium’s cell density based on medium components. This highlighted medium components, and interaction between components, having the most effect on growth: fructose, amino acids, trace elements, CaCl₂, and Na₂HPO₄ contributed significantly to growth (t values of <−1.65 or >1.65); copper and histidine were found to interact and must be balanced for robust growth. Our model was experimentally validated and found to correlate well (r² = 0.85). Model validation at large culture scales showed correlations between our model-predicted growth ranks and experimentally determined ranks at 100 ml in shake flasks (ρ = 0.87) and 1 liter in a bioreactor (ρ = 0.90). Our approach provides valuable and quantifiable insights on the impact of medium components on cell growth and can be applied to model other C. necator responses that are crucial for its deployment as a microbial chassis. This approach can be extended to other nonmodel microbes of medical and industrial biotechnological importance.

IMPORTANCE Chemically defined media (CDM) for cultivation of C. necator vary in components and compositions. This lack of consensus makes it difficult to optimize new processes for the bacterium. This study employed statistical design of experiments (DOE) to understand how basic components of defined media affect C. necator growth. Our growth model predicts that C. necator can be cultivated to high cell density with components held at low concentrations, arguing that CDM for large-scale cultivation of the bacterium for industrial purposes will be economically competitive. Although existing CDM for the bacterium are without amino acids, addition of a few amino acids to growth medium shortened lag phase of growth. The interactions highlighted by our growth model show how factors can interact with each other during a process to positively or negatively affect process output. This approach is efficient, relying on few well-structured experimental runs to gain maximum information on a biological process, growth.

Recent advances in polyhydroxyalkanoate production: Feedstocks, strains and process developments

Polyhydroxyalkanoates (PHAs) have been actively studied in academia and industry for their properties comparable to petroleum-derived plastics and high biocompatibility. However, the major limitation for commercialization is their high cost. Feedstock costs, especially carbon costs, account for the majority of the final cost. Finding cheap feedstocks for PHA production and associated process development are critical for a cost-effective PHA production. In this study, waste materials from different sources, particularly lignocellulosic biomass, were proposed as suitable feedstocks for PHA production. Strains involved in the conversion of these feedstocks into PHA were reviewed. Newly isolated strains were emphasized. Related process development, including the factors that affect PHA production, fermentation modes and downstream processing, was elaborated upon.

Fed-batch cultivation and adding supplements to increase yields of polyhydroxybutyrate production by Cupriavidus necator from corn stover alkaline pretreatment liquor

The aim of this study was to evaluate polyhydroxybutyrate (PHB) production and productivity with supplements under fed-batch cultivation at bioreactor scale (1.3 L). In this study, multiple supplements including oxidative enzyme, mediators, surfactants and silicon nanoparticles were added to Cupriavidus necator culture growing on alkaline pretreatment liquor (APL). At 1.3 L bioreactor scale, PHB production reached 3.3 g/L. To further enhance PHB production, fed-batch cultivation with two different feeding strategies were applied. Under single pulse feeding of 300 mL medium, PHB production reached 4.0 g/L. Under 4 pulses feeding of 75 mL medium each time, PHB production reached 4.5 g/L. This is the highest PHB production from lignin that the authors are aware of in literature.

Chemometric modeling to predict air half-life of persistent organic pollutants (POPs)

We have reported here a quantitative structure-property relationship (QSPR) model for prediction of air half-life of organic chemicals using a dataset of 302 diverse organic chemicals employing only two-dimensional descriptors with definite physicochemical meaning in order to avoid the computational complexity for higher dimensional molecular descriptors. The developed model was rigorously validated using the internationally accepted internal and external validation metrics. The final partial least squares (PLS) regression model obtained at three latent variables comprises six simple and interpretable 2D descriptors. The simple and highly robust model with good quality of predictions explains 66% for the variance of the training set (R²) (64% in terms of LOO variance (Q²)) and 76% for test set variance (R²_pred) (prediction quality). This model might be applicable for data gap filling for determination of POPs in the environment, in case of new or untested chemicals falling within the applicability domain of the model. In general, the model indicates that the air half-life of organic chemicals increases with presence of H-bond acceptor atoms, number of halogen atoms and presence of the R-CH-X fragment and lipophilicity, and decreases with presence of a number of halogens on ring C(sp3) (substitution of halogen atoms on a ring).

Flow cytometry for quantitation of polyhydroxybutyrate production by Cupriavidus necator using alkaline pretreated liquor from corn stover

Alkaline pretreated liquor (APL) from lignocellulosic feedstock pretreatment is a lignin-rich stream. Polyhydroxybutyrate (PHB), a biodegradable polymer, has been previously synthesized from APL. It is of interest to monitor PHB production and cell number from APL rapidly for process control. However, APL has insoluble substances and is dark, which makes quantitation of cells by visible light absorbance difficult. A sample preparation method was developed using Nile Red staining and flow cytometry to quantify bacterial cells and PHB concentration. A linear model with good fitness (R² = 0.9939) was constructed to predict PHB concentration (0.2-2.1 g/L) based on fluorescence intensity acquired from a flow cytometer. A linear model (R² = 0.8614) to predict cell number based on fluorescence intensity was also established. The good correlation between PHB concentration and fluorescence intensity indicates the potential of applying flow cytometry for quantitation of PHB from APL and other media that is dark and/or contains insoluble particles.

Enhancement of polyhydroxybutyrate (PHB) production by 10-fold from alkaline pretreatment liquor with an oxidative enzyme-mediator-surfactant system under Plackett-Burman and central composite designs

In this study, Plackett-Burman and central composite designs were applied to improve polyhydroxybutyrate (PHB) production from alkaline pretreatment liquor (APL) by Cupriavidus necator DSM 545 using a supplement system consisting of oxidative enzymes (laccase, aryl alcohol oxidase (AAO)), mediators (ABTS, HOBT), DMSO, silica nanoparticle Aerosol R816 and surfactant Tween 80. First, screening experiments under Plackett-Burman design showed R816, ABTS and Tween 80 could significantly enhance PHB production. Additional experiments showed that HOBT and DMSO could be removed, and laccase and AAO were needed to remain in the system. Second, a central composite design was applied to obtain the optimum supplemental levels of R816, ABTS and Tween 80. Under optimum conditions, theoretical maximum PHB production (1.9 g/L) was close to experimental PHB production (2.1 g/L). With the supplement system, a 10-fold increase was achieved compared to PHB production (0.2 g/L) without any supplements.

PHA granules help bacterial cells to preserve cell integrity when exposed to sudden osmotic imbalances

Polyhydroxyalkanoates (PHA) are microbial polyesters which accumulate as intracellular granules in numerous prokaryotes and mainly serve as storage materials; beyond this primary function, PHA also enhance the robustness of bacteria against various stress factors. We have observed that the presence of PHA in bacterial cells substantially enhances their ability to maintain cell integrity when suddenly exposed to osmotic imbalances. In the case of the non-halophilic bacterium Cupriavidus necator, the presence of PHA decreased plasmolysis-induced cytoplasmic membrane damage during osmotic up-shock, which subsequently enabled the cells to withstand subsequent osmotic downshock. In contrast, sudden induction of osmotic up- and subsequent down-shock resulted in massive hypotonic lysis of non-PHA containing cells as determined by Transmission Electron Microscopy and Thermogravimetrical Analysis. Furthermore, a protective effect of PHA against hypotonic lysis was also observed in the case of the halophilic bacterium Halomonas halophila; here, challenged PHA-rich cells were capable of retaining cell integrity more effectively than their PHA-poor counterparts. Hence, it appears that the fact that PHA granules, as an added value to their primary storage function, protect halophiles from the harmful effect of osmotic down-shock might explain why PHA accumulation is such a common feature among halophilic prokaryotes. The results of this study, apart from their fundamental importance, are also of practical biotechnological significance: because PHA-rich bacterial cells are resistant to osmotic imbalances, they could be utilized in in-situ bioremediation technologies or during enrichment of mixed microbial consortia in PHA producers under conditions of fluctuating salinity.

Isolation and Characterization of PHA-Producing Bacteria from Propylene Oxide Saponification Wastewater Residual Sludge

A polyhydroxyalkanoate (PHA)-producing strain was isolated from propylene oxide (PO) saponification wastewater activated sludge and was identified as Brevundimonas vesicularis UJN1 through 16S rDNA sequencing and Biolog microbiological identification. Single-factor and response surface methodology experiments were used to optimize the culture medium and conditions. The optimal C/N ratio was 100/1.04, and the optimal carbon and nitrogen sources were sucrose (10 g/L) and NH₄Cl (0.104 g/L) respectively. The optimal culture conditions consisted of initial pH of 6.7 and an incubation temperature of 33.4 °C for 48 h, with 15% inoculum and 100 mL medium at an agitation rate of 180 rpm. The PHA concentration reached 34.1% of the cell dry weight and increased three times compared with that before optimization. The only report of PHA-producing bacteria by Brevundimonas vesicularis showed that the conversion rate of PHAs using glucose as the optimal carbon source was 1.67%. In our research, the conversion rate of PHAs with sucrose as the optimal carbon source was 3.05%, and PHA production using sucrose as the carbon source was much cheaper than that using glucose as the carbon source.

Environmental risk assessment of selected organic chemicals based on TOC test and QSAR estimation models

Environmental risks of organic chemicals have been greatly determined by their persistence, bioaccumulation, and toxicity (PBT) and physicochemical properties. Major regulations in different countries and regions identify chemicals according to their bioconcentration factor (BCF) and octanol-water partition coefficient (Kow), which frequently displays a substantial correlation with the sediment sorption coefficient (Koc). Half-life or degradability is crucial for the persistence evaluation of chemicals. Quantitative structure activity relationship (QSAR) estimation models are indispensable for predicting environmental fate and health effects in the absence of field- or laboratory-based data. In this study, 39 chemicals of high concern were chosen for half-life testing based on total organic carbon (TOC) degradation, and two widely accepted and highly used QSAR estimation models (i.e., EPI Suite and PBT Profiler) were adopted for environmental risk evaluation. The experimental results and estimated data, as well as the two model-based results were compared, based on the water solubility, Kow, Koc, BCF and half-life. Environmental risk assessment of the selected compounds was achieved by combining experimental data and estimation models. It was concluded that both EPI Suite and PBT Profiler were fairly accurate in measuring the physicochemical properties and degradation half-lives for water, soil, and sediment. However, the half-lives between the experimental and the estimated results were still not absolutely consistent. This suggests deficiencies of the prediction models in some ways, and the necessity to combine the experimental data and predicted results for the evaluation of environmental fate and risks of pollutants.

Formal- and high-structured kinetic process modelling and footprint area analysis of binary imaged cells: Tools to understand and optimize multistage-continuous PHA biosynthesis

Competitive polyhydroxyalkanoate (PHAs) production requires progress in microbial strain performance, feedstock selection, downstream processing, and more importantly according to the process design with process kinetics of the microbial growth phase and the phase of product formation. The multistage continuous production in a bioreactor cascade was described for the first time in a continuously operated, flexible five-stage bioreactor cascade that mimics the characteristics involved in the engineering process of tubular plug flow reactors. This process was developed and used for Cupriavidus necator-mediated PHA production at high volumetric and specific PHA productivity (up to 2.31 g/(Lh) and 0.105 g/(gh), respectively). Based on the experimental data, formal kinetic and high structured kinetic models were established, accompanied by footprint area analysis of binary imaged cells. As a result of the study, there has been an enhanced understanding of the long-term continuous PHA production under balanced, transient, and nutrient-deficient conditions that was achieved on both the micro and the macro kinetic level. It can also be concluded that there were novel insights into the complex metabolic occurrences that developed during the multistage- continuous production of PHA as a secondary metabolite. This development was essential in paving the way for further process improvement. At the same time, a new method of specific growth rate and specific production rate based on footprint area analysis was established by using the electron microscope.

Microbial diversity in various types of paper mill sludge: identification of enzyme activities with potential industrial applications

This study is the first comprehensive investigation of enzyme-producing bacteria isolated from four sludge samples (primary, secondary, press and machine) collected in a Kraft paper mill. Overall, 41 strains encompassing 11 different genera were identified by 16S rRNA gene analysis and biochemical testing. Both biodiversity and enzymatic activities were correlated with sludge composition. Press sludge hosted the largest variety of bacterial strains and enzymatic activities, which included hydrolytic enzymes and ligninolytic enzymes. In contrast, strains isolated from secondary sludge were devoid of several enzymatic activities. Most strains were found to metabolize Kraft liquor at its alkaline pH and to decolorize industrial lignin-mimicking dyes. Resistance to lignin or the ability to metabolize this substrate is a prerequisite to survival in any paper mill sludge type. We demonstrate here that the bacterial strains found in a typical Kraft paper mill represent a source of potential novel enzymes for both industrial applications and bioremediation.

Poly-3-hydroxybutyrate (PHB) production from alkylphenols, mono and poly-aromatic hydrocarbons using Bacillus sp. CYR1: A new strategy for wealth from waste

In the present study five different types of alkylphenols, each of the two different types of mono and poly-aromatic hydrocarbons were selected for degradation, and conversion into poly-3-hydroxybutyrate (PHB) using the Bacillus sp. CYR1. Strain CYR1 showed growth with various toxic organic compounds. Degradation pattern of all the organic compounds at 100 mg/l concentration with or without addition of tween-80 were analyzed using high pressure liquid chromatography (HPLC). Strain CYR1 showed good removal of compounds in the presence of tween-80 within 3 days, but it took 6 days without addition of tween-80. Strain CYR1 showed highest PHB production with phenol (51 ± 5%), naphthalene (42 ± 4%), 4-chlorophenol (32 ± 3%) and 4-nonylphenol (29 ± 3%). The functional groups, structure, and thermal properties of the produced PHB were analyzed. These results denoted that the strain Bacillus sp. CYR1 can be used for conversion of different toxic compounds persistent in wastewaters into useable biological polyesters.

Improvement of the poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) production by dual feeding with levulinic acid and sodium propionate in Cupriavidus necator

In the context of increasing volatility of oil prices, replacement of petroleum based plastics by bioplastics is a topic of increasing interest. Poly(hydroxyalkanoate)s (PHAs) are among the most promising families in this field. Controlling composition of the polymer on the monomeric level remains a pivotal issue. This control is even more difficult to achieve when the polymer is not synthesized by chemists, but produced by nature, in this case, bacteria. In this study mechanism and role of two 3-hydroxyvalerate (3-HV) inducing substrates on the production of PHBV with high, 80%, 3-HV content were evaluated. It was found that levulinic acid contributes to biomass and bio-polymer content enhancement, whereas sodium propionate mainly contributes to 3-HV enhancement. Optimized proportions of feeding substrates at 1 g/L and 2.5 g/L, respectively for levulinic acid and sodium propionate allowed a 100% productivity enhancement, at 3.9 mg/L/hour, for the production of PHBV with 80% 3-HV.

Effectiveness of biostimulation through nutrient content on the bioremediation of phenanthrene contaminated soil

Bioremediation has shown its applicability for removal of polycyclic aromatic hydrocarbons (PAHs) from soil and sediments. In the present study, the effect of biostimulation on phenanthrene removal from contaminated soil via adding macro and/or micronutrients and trace elements was investigated. For these purposes three macro nutrients (as N, P and K), eight micronutrients (as Mg, S, Fe, Cl, Zn, Mn, Cu and Na) and four trace elements (as B, Mo, Co and Ni) in 11 mineral salts (MS) as variables were used. Placket-Burman statistical design was used to evaluate significance of variables (MS) in two levels of high and low. A consortium of adapted microorganisms with PAHs was used for inoculation to the soil slurry which was spiked with phenanthrene in concentration of 500 mg/kg soil. The optimal reduction resulted when a high level of macro nutrient in the range of 67-87% and low level of micro nutrient in the range of 12-32% were used with the nitrogen as the dominant macronutrient. The Pareto chart showed that NH4NO3 was the most effective variable in this experiment. The effect of elements on phenanthrene biodegradation showed following sequence as N > K > P > Cl > Na > Mg. Effectiveness of the other elements in all runs was less than 1%. The type and concentration of nutrient can play an important role in biodegradation of phenanthrene. Biostimulation with suitable combination of nutrient can enhance bioremediation of PAHs contaminated soils.