Assessing interactions, predicting function, and increasing degradation potential of a PAH-degrading bacterial consortium by effect of an inoculant strain

Genome analysis for the identification of genes involved in phenanthrene biodegradation pathway in Stenotrophomonas indicatrix CPHE1. Phenanthrene mineralization in soils assisted by integrated approaches

Phenanthrene (PHE) is a highly toxic compound, widely present in soils. For this reason, it is essential to remove PHE from the environment. Stenotrophomonas indicatrix CPHE1 was isolated from an industrial soil contaminated by polycyclic aromatic hydrocarbons (PAHs) and was sequenced to identify the PHE degrading genes. Dioxygenase, monooxygenase, and dehydrogenase gene products annotated in S. indicatrix CPHE1 genome were clustered into different trees with reference proteins. Moreover, S. indicatrix CPHE1 whole-genome sequences were compared to genes of PAHs-degrading bacteria retrieved from databases and literature. On these basis, reverse transcriptase-polymerase chain reaction (RT-PCR) analysis pointed out that cysteine dioxygenase (cysDO), biphenyl-2,3-diol 1,2-dioxygenase (bphC), and aldolase hydratase (phdG) were expressed only in the presence of PHE. Therefore, different techniques have been designed to improve the PHE mineralization process in five PHE artificially contaminated soils (50 mg kg^-1), including biostimulation, adding a nutrient solution (NS), bioaugmentation, inoculating S. indicatrix CPHE1 which was selected for its PHE-degrading genes, and the use of 2-hydroxypropyl-β-cyclodextrin (HPBCD) as a bioavailability enhancer. High percentages of PHE mineralization were achieved for the studied soils. Depending on the soil, different treatments resulted to be successful; in the case of a clay loam soil, the best strategy was the inoculation of S. indicatrix CPHE1 and NS (59.9% mineralized after 120 days). In sandy soils (CR and R soils) the highest percentage of mineralization was achieved in presence of HPBCD and NS (87.3% and 61.3%, respectively). However, the combination of CPHE1 strain, HPBCD, and NS showed to be the most efficient strategy for sandy and sandy loam soils (LL and ALC soils showed 35% and 74.6%, respectively). The results indicated a high degree of correlation between gene expression and the rates of mineralization.

Enhanced Bioremediation of Aged Polycyclic Aromatic Hydrocarbons in Soil Using Immobilized Microbial Consortia Combined with Strengthening Remediation Strategies

Microbial biodegradation is considered as one of the most effective strategies for the remediation of soil contaminated with polycyclic aromatic hydrocarbons (PAHs). To improve the degradation efficiency of PAHs, PAH-degrading consortia combined with strengthening remediation strategies was used in this study. The PAH biodegrading performance of seven bacterial consortia constructed by different ratios of Mycobacterium gilvum MI, Mycobacterium sp. ZL7 and Rhodococcus rhodochrous Q3 was evaluated in an aqueous system containing phenanthrene, pyrene, benzo[a]pyrene and benzo[b]fluoranthene. Bacterial consortium H6 (Q3:ZL7:MI = 1:2:2) performed a high degrading efficiency of 59% in 8 days. The H6 was subsequently screened to explore its potential ability and performance to degrade aged PAHs in soils from a coking plant and the effects of strengthening strategies on the aged PAH degradation, including the addition of glucose or sodium dodecyl benzene sulfonate (SDBS) individually or as a mixture along immobilization of the inoculant on biochar. The highest degradation efficiencies, which were 15% and 60% for low-molecular-weight (LMW) PAHs and high-molecular-weight (HMW) PAHs, respectively, were observed in the treatment using immobilized microbial consortium H6 combined with the addition of glucose and SDBS after 24 days incubation. This study provides new insights and guidance for future remediation of aged PAH contaminated soils.

Effects of organic matter addition on chronically hydrocarbon-contaminated soil

Soil is the recipient of organic pollutants as a consequence of anthropogenic activities. Hydrocarbons are contaminants that pose a risk to human and environmental health. Bioremediation of aging contaminated soils is a challenge due to the low biodegradability of contaminants as a result of their interaction with the soil matrix. The aim of this work was to evaluate the effect of both composting and the addition of mature compost on a soil chronically contaminated with hydrocarbons, focusing mainly on the recovery of soil functions and transformations of the soil matrix as well as microbial community shifts. The initial pollution level was 214 ppm of polycyclic aromatic hydrocarbons (PAHs) and 2500 ppm of aliphatic hydrocarbons (AHs). Composting and compost addition produced changes on soil matrix that promoted the release of PAHs (5.7 and 15 % respectively) but not the net PAH elimination. Interestingly, composting stimulated AHs elimination (about 24 %). The lack of PAHs elimination could be attributed to the insufficient PAHs content to stimulate the microbial degrading capacity, and the preferential consumption of easily absorbed C sources by the bacterial community. Despite the low PAH catabolic potential of the aging soil, metabolic shift was driven by the addition of organic matter, which could be monitored by the ratio of Proteobacteria to Actinobacteria combined with E₄/E₆ ratio. Regarding the quality of the soil, the nutrients provided by the exogenous organic matter contributed to the recovery of the global functions and species diversity of the soil along with the reduction of phytotoxicity.