Enhanced degradation of polycyclic aromatic hydrocarbons (PAHs) in the rhizosphere of sudangrass (Sorghum × drummondii)

Rice husk and its derived biochar assist phytoremediation of heavy metals and PAHs co-contaminated soils but differently affect bacterial community

In order to evaluate the feasibility of rice husk and rice husk biochar on assisting phytoremediation of polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs) co-contaminated soils, a 150-day pot experiment planted with alfalfa was designed. Rice husk and its derived biochar were applied to remediate a PAHs, Zn, and Cr co-contaminated soil. The effects of rice husk and biochar on the removal and bioavailability of PAHs and HMs, PAH-ring hydroxylating dioxygenase gene abundance and bacterial community structure in rhizosphere soils were investigated. Results suggested that rice husk biochar had better performance on the removal of PAHs and immobilization of HMs than those of rice husk in co-contaminated rhizosphere soil. The abundance of PAH-degraders, which increased with the culture time, was positively correlated with PAHs removal. Rice husk biochar decreased the richness and diversity of bacterial community, enhanced the growth of Steroidobacter, Bacillus, and Sphingomonas in rhizosphere soils. However, Steroidobacter, Dongia and Acidibacter were stimulated in rice husk amended soils. According to the correlation analysis, Steroidobacter and Mycobacterium may play an important role in PAHs removal and HMs absorption. The combination of rice husk biochar and alfalfa would be a promising method to remediate PAHs and HMs co-contaminated soil.

Transfer and Degradation of PAHs in the Soil-Plant System: A Review

Polycyclic aromatic hydrocarbons (PAHs) are highly toxic, persistent organic pollutants that threaten ecosystems and human health. Consistent monitoring is essential to minimize the entry of PAHs into plants and reduce food chain contamination. PAHs infiltrate plants through multiple pathways, causing detrimental effects and triggering diverse plant responses, ultimately increasing either toxicity or tolerance. Primary plant detoxification processes include enzymatic transformation, conjugation, and accumulation of contaminants in cell walls/vacuoles. Plants also play a crucial role in stimulating microbial PAHs degradation by producing root exudates, enhancing bioavailability, supplying nutrients, and promoting soil microbial diversity and activity. Thus, synergistic plant-microbe interactions efficiently decrease PAHs uptake by plants and, thereby, their accumulation along the food chain. This review highlights PAHs uptake pathways and their overall fate as contaminants of emerging concern (CEC). Understanding plant uptake mechanisms, responses to contaminants, and interactions with rhizosphere microbiota is vital for addressing PAH pollution in soil and ensuring food safety and quality.

Rice genotypes and root-associated niches shifted bacterial community in response to pollution of di-(2-ethylhexyl) phthalate (DEHP) for promoting DEHP removal

Organic pollutants influenced root-associated bacterial community. However, the response variation of root-associated bacterial community among different rice genotypes exposed to phthalates (PAEs) and their removal mechanism remains unknown. Here, bacterial community and PAE-degrading genes in root-associated niches were analyzed between low (Fengyousimiao) and high (Hhang) PAE-accumulating rice cultivars exposed to di-(2-ethylhexyl) phthalate (DEHP). DEHP dissipation percentages in rhizosphere of Hhang were significantly higher than those of Fengyousimiao. The bacterial community diversities (including Chao1 and Shannon index) significantly decreased along bulk soil - rhizosphere - rhizoplane - endosphere. The bacterial community structures were shaped mainly by root-associated niches, DEHP pollution and rice genotypes, with significant differences in rhizosphere and rhizoplane between Fengyousimiao and Hhang. Rhizosphere enriched more PAE-degrading bacteria than in bulk soil, and exhibited significantly higher expression of PAE-degrading genes (hydrolase 65, phtab, phtC, pcaF and pcaI) than in bulk soil. Furthermore, rhizosphere of Hhang demonstrated significantly stronger bacterial functions related to xenobiotics biodegradation and higher expression of PAE-degrading genes than those of Fengyousimiao, leading to significantly higher DEHP dissipation percentages in rhizosphere of Hhang. The findings demonstrate that Hhang shaped specific root-associated bacterial community with higher abundances of PAE-degrading bacteria and genes than Fengyousimiao to promote DEHP degradation.

Revealing the key species for pyrene degradation in Vallisneria natans rhizosphere sediment via triple chamber rhizome-box experiments

To identify key species associated with pyrene degradation in Vallisneria natans (V.natans) rhizosphere sediment, this work investigated the temporal and spatial changes in the rhizosphere microbial community and the relationship between the changes and the pyrene degradation process through a three-compartment rhizome-box experiment under pyrene stress. The degradation kinetics of pyrene showed that the order of degradation rate was rhizosphere > near-rhizosphere > non-rhizosphere. The difference in the pyrene degradation behavior in the sediments corresponded to the change in the proportions of dominant phyla (Firmicutes and Proteobacteria) and genera (g_Massilia f_Comamonadaceae, g_Sphingomonas). The symbiosis networks and hierarchical clustering analysis indicated that the more important phyla related to the pyrene degradation in the rhizosphere was Proteobacteria, while g_Sphigomonas, f_Comamonadaceae, and especially g_Massilia were the core genera. Among them, f_Comamonadaceae was the genus most affected by rhizosphere effects. These findings strengthened our understanding of the PAHs-degradation microorganisms in V.natans rhizosphere and are of great significance for enhancing phytoremediation on PAHs-contaminated sediment.

Biodegradation of polycyclic aromatic hydrocarbons (PAHs) by microbial consortium from paddy rice soil

Polycyclic aromatic hydrocarbons (PAHs) are among the most widely spread pollutants in the environment including the agricultural soil. PAH degradation by indigenous bacteria is an effective and economical means to remove these pollutants from the environment. Here, we report a bacterial consortium (Pdy-1) isolated from paddy rice soil in northern Japan able to degrade polycyclic aromatic hydrocarbons (PAHs) at high rates. Pdy-1 was incubated with a mixture of PAH compounds (fluorene, phenanthrene, and pyrene) in Bushnell Haas Medium at a final concentration of 100 mg/L each. PDY-1 degraded 100% of fluorene, 95% of phenanthrene, and 52% of pyrene in 5 days. Phenanthrene and pyrene were completely degraded at 10 d and 15 d, respectively. Cloning of the 16S rRNA gene revealed that the consortium was composed of 40% Achromobacter and 7% each of Castelaniella, Rhodanobacter, and Hypomicrobium. Comamonas, Ferrovibrio, Terrimonas, Bordetella, Rhizobium, and Pseudonocardia were also detected. PCR-DGGE showed the dynamics of the consortium during the incubation period. Real-time PCR revealed that PAH degrading genes such as the gram-positive ring dihydroxylating genes (PAH-RDH) and pyrene dioxygenase (nidA) were most abundant at day 5 when the rapid biodegradation of the PAHs was observed. This study improves our understanding on dynamics and characteristics of an effective PAH-degrading bacterial consortium from paddy rice soil.

The Relationship between Brachionus calyciflorus-Associated Bacterial and Bacterioplankton Communities in a Subtropical Freshwater Lake

Zooplankton bodies are organic-rich micro-environments that support fast bacterial growth. Therefore, the abundance of zooplankton-associated bacteria is much higher than that of free-living bacteria, which has profound effects on the nutrient cycling of freshwater ecosystems. However, a detailed analysis of associated bacteria is still less known, especially the relationship between those bacteria and bacterioplankton. In this study, we analyzed the relationships between Brachionus calyciflorus-associated bacterial and bacterioplankton communities in freshwater using high-throughput sequencing. The results indicated that there were significant differences between the two bacterial communities, with only 29.47% sharing OTUs. The alpha diversity of the bacterioplankton community was significantly higher than that of B. calyciflorus-associated bacteria. PCoA analysis showed that the bacterioplankton community gathered deeply, while the B. calyciflorus-associated bacterial community was far away from the whole bacterioplankton community, and the distribution was relatively discrete. CCA analysis suggested that many environmental factors (T, DO, pH, TP, PO₄^3-, NH₄⁺, and NO₃^-) regulated the community composition of B. calyciflorus-associated bacteria, but the explanatory degree of variability was only 37.80%. High-throughput sequencing revealed that Raoultella and Delftia in Proteobacteria were the dominant genus in the B. calyciflorus-associated bacterial community, and closely related to the biodegradation function. Moreover, several abundant bacterial members participating in carbon and nitrogen cycles were found in the associated bacterial community by network analysis. Predictive results from FAPROTAX showed that the predominant biogeochemical cycle functions of the B. calyciflorus-associated bacterial community were plastic degradation, chemoheterotrophy, and aerobic chemoheterotrophy. Overall, our study expands the current understanding of zooplankton-bacteria interaction and promotes the combination of two different research fields.

Effect of soil contamination with polycyclic aromatic hydrocarbons from drilling waste on germination and growth of lawn grasses

In many studies, grasses were used to increase the biodegradation of polycyclic aromatic hydrocarbons (PAHs) in soil because they are the most common plant species on the ground level and are quite resistant to contamination with these compounds. One of the main failures in PAH remediation in soil using plant species was the negative impact on germination and seedling growth. The objective of this study was to evaluate grass seed germination and seedling growth affected by drill cuttings to determine the resistance of selected grass species to the impact of PAH and their suitability for an effective phytoremediation of soils contaminated with waste that contain compounds from this group. In the study four grass species: tall fescue (Festuca arundinacea), red fescue (Festuca rubra), perennial ryegrass (Lolium perenne) and common meadow-grass (Poa pratensis). The germination energy of all species decreased as the amount of drill cuttings increased. Among the species studied, the highest germination energy and capacity were found in Lolium perenne (54.1 and 73.2 respectively), and the lowest - in Poa pratensis (16.7 and 23.3 respectively). With an increasing amount of drill cuttings, the root and seedling height were decreased. Festuca arundinacea seedlings were distinctly the highest and had the longest roots (96.7 and 52.7, respectively), while Poa pratensis seedlings showed the significantly slowest seedling and root elongation rate (30.4 and 12.4, respectively). However, the strongest decrease in seedling height and root length compared to the control was observed in Festuca rubra. Based on IC50, the greatest tolerance to the addition of drilling waste to the substrate was found for Festuca arundinacea and Festuca rubra. The conducted investigation indicates that Festuca arundinacea and Lolium perenne are grass species that are least sensitive to drilling waste in the substrate because no significant differences were found in root length and seedling height between the control soil and the soil where a PAH dose of 5% and 10% was applied.

From Surface Water to the Deep Sea: A Review on Factors Affecting the Biodegradation of Spilled Oil in Marine Environment

Over the past century, the demand for petroleum products has increased rapidly, leading to higher oil extraction, processing and transportation, which result in numerous oil spills in coastal-marine environments. As the spilled oil can negatively affect the coastal-marine ecosystems, its transport and fates captured a significant interest of the scientific community and regulatory agencies. Typically, the environment has natural mechanisms (e.g., photooxidation, biodegradation, evaporation) to weather/degrade and remove the spilled oil from the environment. Among various oil weathering mechanisms, biodegradation by naturally occurring bacterial populations removes a majority of spilled oil, thus the focus on bioremediation has increased significantly. Helping in the marginal recognition of this promising technique for oil-spill degradation, this paper reviews recently published articles that will help broaden the understanding of the factors affecting biodegradation of spilled oil in coastal-marine environments. The goal of this review is to examine the effects of various environmental variables that contribute to oil degradation in the coastal-marine environments, as well as the factors that influence these processes. Physico-chemical parameters such as temperature, oxygen level, pressure, shoreline energy, salinity, and pH are taken into account. In general, increase in temperature, exposure to sunlight (photooxidation), dissolved oxygen (DO), nutrients (nitrogen, phosphorous and potassium), shoreline energy (physical advection—waves) and diverse hydrocarbon-degrading microorganisms consortium were found to increase spilled oil degradation in marine environments. In contrast, higher initial oil concentration and seawater pressure can lower oil degradation rates. There is limited information on the influences of seawater pH and salinity on oil degradation, thus warranting additional research. This comprehensive review can be used as a guide for bioremediation modeling and mitigating future oil spill pollution in the marine environment by utilizing the bacteria adapted to certain conditions.

The Influence of Kerosene on Microbiomes of Diverse Soils

One of the most important challenges for soil science is to determine the limits for the sustainable functioning of contaminated ecosystems. The response of soil microbiomes to kerosene pollution is still poorly understood. Here, we model the impact of kerosene leakage on the composition of the topsoil microbiome in pot and field experiments with different loads of added kerosene (loads up to 100 g/kg; retention time up to 360 days). At four time points we measured kerosene concentration and sequenced variable regions of 16S ribosomal RNA in the microbial communities. Mainly alkaline Dystric Arenosols with low content of available phosphorus and soil organic matter had an increased fraction of Actinobacteriota, Firmicutes, Nitrospirota, Planctomycetota, and, to a lesser extent, Acidobacteriota and Verrucomicobacteriota. In contrast, in highly acidic Fibric Histosols, rich in soil organic matter and available phosphorus, the fraction of Acidobacteriota was higher, while the fraction of Actinobacteriota was lower. Albic Luvisols occupied an intermediate position in terms of both physicochemical properties and microbiome composition. The microbiomes of different soils show similar response to equal kerosene loads. In highly contaminated soils, the proportion of anaerobic bacteria-metabolizing hydrocarbons increased, whereas the proportion of aerobic bacteria decreased. During the field experiment, the soil microbiome recovered much faster than in the pot experiments, possibly due to migration of microorganisms from the polluted area. The microbial community of Fibric Histosols recovered in 6 months after kerosene had been loaded, while microbiomes of Dystric Arenosols and Albic Luvisols did not restore even after a year.

Biodegradation of binary mixtures of octane with benzene, toluene, ethylbenzene or xylene (BTEX): insights on the potential of Burkholderia, Pseudomonas and Cupriavidus isolates

The contamination of the environment by crude oil and its by-products, mainly composed of aliphatic and aromatic hydrocarbons, is a widespread problem. Biodegradation by bacteria is one of the processes responsible for the removal of these pollutants. This study was conducted to determine the abilities of Burkholderia sp. B5, Cupriavidus sp. B1, Pseudomonas sp. T1, and another Cupriavidus sp. X5 to degrade binary mixtures of octane (representing aliphatic hydrocarbons) with benzene, toluene, ethylbenzene, or xylene (BTEX as aromatic hydrocarbons) at a final concentration of 100 ppm under aerobic conditions. These strains were isolated from an enriched bacterial consortium (Yabase or Y consortium) that prefer to degrade aromatic hydrocarbon over aliphatic hydrocarbons. We found that B5 degraded all BTEX compounds more rapidly than octane. In contrast, B1, T1 and X5 utilized more of octane over BTX compounds. B5 also preferred to use benzene over octane with varying concentrations of up to 200 mg/l. B5 possesses alkane hydroxylase (alkB) and catechol 2,3-dioxygenase (C23D) genes, which are responsible for the degradation of alkanes and aromatic hydrocarbons, respectively. This study strongly supports our notion that Burkholderia played a key role in the preferential degradation of aromatic hydrocarbons over aliphatic hydrocarbons in the previously characterized Y consortium. The preferential degradation of more toxic aromatic hydrocarbons over aliphatics is crucial in risk-based bioremediation.

Effects of Fire Phoenix (a genotype mixture of Fesctuca arundinecea L.) and Mycobacterium sp. on the degradation of PAHs and bacterial community in soil

Phytomicrobial remediation technology of PAH-contaminated soils has drawn great attention due to its low-cost, eco-friendly, and effective characteristics, but the mechanism underlying the removal of PAHs by rhizosphere in wastewater-irrigated soil is so far not clear. To evaluate the dissipation of PAHs and the shifts of bacterial community structure under plant-microorganism symbiotic system in an agricultural soil, a rhizo-box experiment with Fire Phoenix (a genotype mixture of Fesctuca arundinecea L.) or/and inoculated Mycobacterium sp. was conducted for 60 days. The changes of bacterial community structure and the contents of PAHs were analyzed by denaturing gradient gel electrophoresis (DGGE) and high-performance liquid chromatography (HPLC), respectively. The results showed that the removal rate of PAHs in phytomicrobial combined treatment was 53.7% after 60 days. The PAH-degraders were dominated by Microbacterium sp., Sphingomonas sp., Mycobacterium sp., and Flavobacterium sp. The plant of Fire Phoenix induced the appearance of Pseudomonas sp. and TM7 phylum sp. oral clone. The highest of bacterial diversity index was observed in unrhizosphere soils (MR-), rather than that in rhizosphere soils (MR+). In combination, phytomicrobial combined treatment of Fire Phoenix and Mycobacterium strain enhanced the removal rate of PAHs and changed the structure of bacterial community and bacterial diversity. Bacterial community has great effect on PAH degradation in PAH-contaminated soil from the wastewater-irrigated site. Our study can provide support information for PAH degradation enhancement by the synergetic effect of Fire Phoenix and Mycobacterium sp.

Genes related to redox and cell curvature facilitate interactions between Caulobacter strains and Arabidopsis

Bacteria play an integral role in shaping plant growth and development. However, the genetic factors that facilitate plant-bacteria interactions remain largely unknown. Here, we demonstrated the importance of two bacterial genetic factors that facilitate the interactions between plant-growth-promoting (PGP) bacteria in the genus Caulobacter and the host plant Arabidopsis. Using homologous recombination, we disrupted the cytochrome ubiquinol oxidase (cyo) operon in both C. vibrioides CB13 and C. segnis TK0059 by knocking out the expression of cyoB (critical subunit of the cyo operon) and showed that the mutant strains were unable to enhance the growth of Arabidopsis. In addition, disruption of the cyo operon, metabolomic reconstructions, and pH measurements suggested that both elevated cyoB expression and acid production by strain CB13 contribute to the previously observed inhibition of Arabidopsis seed germination. We also showed that the crescent shape of the PGP bacterial strain C. crescentus CB15 contributes to its ability to enhance plant growth. Thus, we have identified specific genetic factors that explain how select Caulobacter strains interact with Arabidopsis plants.

Assessment of PAH degradation potential of native species from a coking plant through identifying of the beneficial bacterial community within the rhizosphere soil

Understanding the mechanisms underlying plant-rhizobacteria interactions in field-contaminated soils is crucial for designing effective rhizoremediation strategies. This study aimed to test the ability of four native herb species to remove polycyclic aromatic hydrocarbons (PAHs) and to analyze their associated bacterial community structures and functional genes within the rhizosphere from the abandoned site of a former Shenyang coking plant in China; the bulk soil was collected as control. All four species removed PAHs, of which the rhizosphere of Kochia scoparia had the highest PAH removal rate (almost 30.2%). Although the composition of the bacterial community within the rhizosphere varied among plant species, all plant species could promote the growth of Sphingomonas, Pedomicrobium, Rhodoplanes, Blastoccus, Mycobacterium, Devosia, and Pseudomonas, and their relative abundance positively correlated with the removal rates of PAHs, soil moisture, and total carbon/total nitrogen in the rhizosphere. Moreover, the activities of 1-aminocyclopropane-1 -carboxylic deaminase gene and Gram-negative ring-hydroxylating dioxygenase gene significantly (P < 0.05) increased compared with those in the control, and these activities had a strong positive correlation with the removal rates of PAHs [r = 0.759 (P < 0.01) and 0.87 (P < 0.01), respectively]. The findings of this study indicated that PAHs were the main factor driving the composition of beneficial bacteria in PAH rhizodegradation, and the PAH rhizoremediation of native plants grown in coking plant can be controlled though altering soil properties.

Initial oil concentration affects hydrocarbon biodegradation rates and bacterial community composition in seawater

During oil spills in the field or for laboratory incubation studies, different oil concentrations are often encountered or applied, yet how initial oil concentration affects biodegradation rates of hydrocarbons and the development of oil degraders remains unclear. We incubated seawater for 50 d with different oil concentrations (0, 50, 100, 200, 400 and 800 ppm). n-Alkanes and polycyclic aromatic hydrocarbons (PAHs), and the bacterial community were analyzed periodically. Results show that the biodegradation rates of alkanes, derived from first order kinetics, decreased with increasing oil concentration, but percent residual was ~50% regardless of the initial concentration. In contrast, the biodegradation rates of PAHs increased with concentration, and the percent residual increased with oil concentration. Increasing oil concentration resulted in increased abundances of Rhodobacterales, Altererythrobacter, and Neptuniibacter. However, Alcanivorax abundance was barely detected in 400 and 800 ppm. Overall, oil concentration critically affected the degradation of hydrocarbons and the bacterial community.

Response of soil bacterial communities to polycyclic aromatic hydrocarbons during the phyto-microbial remediation of a contaminated soil

Rhizo-box experiments were conducted to analyze the phyto-microbial remediation potential of a grass (Lolium multiflorum L.) and a crop (Glycine max L.) combined with exogenous strain (Pseudomonas sp.) for polycyclic aromatic hydrocarbons (PAHs) contaminated soils. The dynamics of bacterial community composition, abundances of 16 S rDNA and ring hydroxylating dioxygenases (RHDα) genes, and removal of PAHs were evaluated and compared on four culture stages (days 0, 10, 20, and 30). The results showed that 8.65%-47.42% of Σ12 PAHs were removed after 30 days of cultivation. Quantitative polymerase chain reaction (qPCR) analysis indicated that treatments with soybean and ryegrass rhizosphere markedly increased the abundances of total bacteria and PAH-degraders, especially facilitated the growth of gram-negative degrading bacteria. Flavobacterium sp. and Pseudomonas sp. were the main and active strains in the control soil. However, the presence of plants and/or exogenous Pseudomonas sp. changed the soil bacterial community structure and modified the bacterial diversity of PAH-degraders. On the whole, this study showed that the high molecular weight PAHs removal efficiency of phyto-microbial remediation with ryegrass was better than those of remediation with soybean. Furthermore, the removals of PAHs strongly coincided with the abundance of PAH-degraders and bacterial community structure.

Marine Snow Aggregates are Enriched in Polycyclic Aromatic Hydrocarbons (PAHs) in Oil Contaminated Waters: Insights from a Mesocosm Study

Marine snow was implicated in the transport of oil to the seafloor during the Deepwater Horizon oil spill, but the exact processes remain controversial. In this study, we investigated the concentrations and distributions of the 16 USEPA priority polycyclic aromatic hydrocarbons (PAHs) in marine snow aggregates collected during a mesocosm experiment. Seawater only, oil in a water accommodated fraction (WAF), and Corexit-enhanced WAF (DCEWAF) were incubated for 16 d. Both WAF and DCEWAF aggregates were enriched in heavy molecular weight PAHs but depleted in naphthalene. DCEWAF aggregates had 2.6 times more total 16 PAHs than the WAF (20.5 vs. 7.8 µg/g). Aggregates in the WAF and DCEWAF incorporated 4.4% and 19.3%, respectively of the total PAHs in the mesocosm tanks. Our results revealed that marine snow sorbed and scavenged heavy molecular weight PAHs in the water column and the application of Corexit enhanced the incorporation of PAHs into the sinking aggregates.

Polycyclic aromatic hydrocarbons (PAHs) and putative PAH-degrading bacteria in Galveston Bay, TX (USA), following Hurricane Harvey (2017)

Hurricane Harvey was the wettest hurricane in US history bringing record rainfall and widespread flooding in Houston, TX. The resulting storm- and floodwaters largely emptied into the Galveston Bay. Surface water was collected from 10 stations during five cruises to investigate the concentrations and sources of 16 priority polycyclic aromatic hydrocarbons (PAHs), and relative abundances of PAH-degrading bacteria. Highest PAH levels (102-167 ng/L) were detected during the first sampling event, decreasing to 36-69 ng/L within a week. Four sites had elevated concentrations of carcinogenic benzo[a]pyrene that exceeded the Texas Standard for Surface Water threshold. The highest relative abundances of known PAH-degrading bacteria Burkholderiaceae, Comamonadaceae, and Sphingomonadales were detected during the first and second sampling events. PAH origins were about 60% pyrogenic, 2% petrogenic, and the remainder of mixed sources. This study improves our understanding on the fate, source, and distributions of PAHs in Galveston Bay after an extreme flooding event.

Nano-SiO2 combined with a surfactant enhanced phenanthrene phytoremediation by Erigeron annuus (L.) Pers

The objective of this experiment was to evaluate the effects of Triton X-100 (1000 mg kg^-1) and nano-SiO₂ (500 mg kg^-1) on Erigeron annuus (L.) Pers. grown in phenanthrene spiked soil (150 mg kg^-1) for 60 days. Results show that untreated groups, groups treated with both Triton X-100 and nano-SiO₂, exhibited better phenanthrene degradation rates and improved root biomasses, chlorophyll contents, and soil enzyme activities. This study demonstrates that Triton X-100 combined with nano-SiO₂ protects plants, alleviating the stress of polycyclic aromatic hydrocarbons (PAHs), and can provide a means for improving phytoremediation of PAH contaminated soils.

Hydroponic approach to assess rhizodegradation by sudangrass (Sorghum x drummondii) reveals pH- and plant age-dependent variability in bacterial degradation of polycyclic aromatic hydrocarbons (PAHs)

Rhizodegradation of polycyclic aromatic hydrocarbons (PAHs) is a product of complex interactions between plant and bacteria. In this study, hydroponic culture of sudangrass was established in order to investigate the effects of the plant on PAHs degradation and vice versa through changes in rhizosphere bacterial community. Results showed a plant-induced variability in PAHs degradation dependent on a characteristic shift in bacterial community, with pH and plant age as driving factors. Moreover, bacterial communities with high diversity seemed to abate the phytotoxic effects of PAHs degradation as observed in the plant's gross health. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and next-generation sequencing revealed that regardless of plant age and culture conditions, the increase or decrease of Sphingobium sp. could dictate the PAHs degradation potential of the bacterial consortium. Overall, this study utilized hydroponic culture of sudangrass to show that plant even of same species can suppress, support, or enhance PAHs degradation of bacteria depending on specific factors.

Microbial diversity and metaproteomic analysis of activated sludge responses to naphthalene and anthracene exposure

The activated sludge process can effectively remove polycyclic aromatic hydrocarbons (PAHs) from wastewater via biodegradation. However, the degradable microorganisms and functional enzymes involved in this process remain unclear. In this study, we successfully employed a laboratory-scale sequential batch reactor to investigate variations in microbial community and protein expression in response to the addition of different PAHs and process time. The analysis of bacterial community structure by 454 pyrosequencing of the 16S rRNA gene indicated that bacteria from Burkholderiales order were dominant in PAHs treated sludge. Mass spectrometry performed with 2D protein profiles of all sludge samples demonstrated that most proteins exhibiting differential expression profiles during the process were derived from Burkholderiales populations; these proteins are involved in DNA replication, fatty acid and glucose metabolism, stress response, protein synthesis, and aromatic hydrocarbon metabolism. Nevertheless, the protein expression profiles indicated that naphthalene, but not anthracene, can induce the expression of PAH-degrading proteins and accelerate its elimination from sludge. Though only naphthalene and anthracene were added into our experimental groups, the differentially expressed enzymes involved in other PAHs (especially biphenyl) metabolism were also detected. This study provides apparent evidence linking the metabolic activities of Burkholderiales populations with the degradation of PAHs in activated sludge processes. Overall, our findings highlighted the successful application of metaproteomics integrated with microbial diversity analysis by high-throughput sequencing technique on the analysis of environmental samples, which could provide a convenience to monitor the changes in proteins expression profiles and their correlation with microbial diversity.

The change of dominant microorganisms and protein expression profiles in PAHs stress in sludge reactors were investigated. Burkholderiales was dominant in response to PAH. Naphthalene induces the expression of PAH-degrading proteins.