Analyzing the microbial community structure and functions become imperative for ecological processes. To understand the impact of spent engine oil (SEO) contamination on microbial community structure of an agricultural soil, soil microcosms designated 1S (agricultural soil) and AB1 (agricultural soil polluted with SEO) were set up. Metagenomic DNA extracted from the soil microcosms and sequenced using Miseq Illumina sequencing were analyzed for their taxonomic and functional properties. Taxonomic profiling of the two microcosms by MG-RAST revealed the dominance of Actinobacteria (23.36%) and Proteobacteria (52.46%) phyla in 1S and AB1 with preponderance of Streptomyces (12.83%) and Gemmatimonas (10.20%) in 1S and Geodermatophilus (26.24%), Burkholderia (15.40%), and Pseudomonas (12.72%) in AB1, respectively. Our results showed that soil microbial diversity significantly decreased in AB1. Further assignment of the metagenomic reads to MG-RAST, Cluster of Orthologous Groups (COG) of proteins, Kyoto Encyclopedia of Genes and Genomes (KEGG), GhostKOALA, and NCBI's CDD hits revealed diverse metabolic potentials of the autochthonous microbial community. It also revealed the adaptation of the community to various environmental stressors such as hydrocarbon hydrophobicity, heavy metal toxicity, oxidative stress, nutrient starvation, and C/N/P imbalance. To the best of our knowledge, this is the first study that investigates the effect of SEO perturbation on soil microbial communities through Illumina sequencing. The results indicated that SEO contamination significantly affects soil microbial community structure and functions leading to massive loss of nonhydrocarbon degrading indigenous microbiota and enrichment of hydrocarbonoclastic organisms such as members of Proteobacteria and Actinobacteria.

The effects of corn steep liquor (CSL) on hydrocarbon degradation and microbial community structure and function was evaluated in field-moist soil microcosms. Chronically polluted soil treated with CSL (AB4) and an untreated control (3S) was compared over a period of 6 weeks. Gas chromatographic fingerprints of residual hydrocarbons revealed removal of 95.95% and 94.60% aliphatic and aromatic hydrocarbon fractions in AB4 system with complete disappearance of nC 1-nC 8 , nC 10 , nC 15 , nC 20-nC 23 aliphatics and aromatics such as naphthalene, acenaphthylene, fluorene, phenanthrene, pyrene, benzo(a)anthracene, and indeno(123-cd)pyrene in 42 days. In 3S system, there is removal of 61.27% and 66.58% aliphatic and aromatic fractions with complete disappearance of nC 2 and nC 21 aliphatics and naphthalene, acenaphthylene, fluorene, phenanthrene, pyrene, and benzo(a)anthracene aromatics in 42 days. Illumina shotgun sequencing of the DNA extracted from the two systems showed the preponderance of Actinobacteria (31.46%) and Proteobacteria (38.95%) phyla in 3S and AB4 with the dominance of Verticillium (22.88%) and Microbacterium (8.16%) in 3S, and Laceyella (24.23%), Methylosinus (8.93%) and Pedobacter (7.73%) in AB4. Functional characterization of the metagenomic reads revealed diverse metabolic potentials and adaptive traits of the microbial communities in the two systems to various environmental stressors. It also revealed the exclusive detection of catabolic enzymes in AB4 system belonging to the aldehyde dehydrogenase superfamily. The results obtained in this study showed that CSL is a potential resource for bioremediation of hydrocarbon-polluted soils.

No abstract

The last two decades had witnessed extensive investigation on bacterial degradation of carbazole, an Nheterocyclic aromatic hydrocarbon. Specifically, previous studies have reported the primary importance of angular dioxygenation, a novel type of oxygenation reaction, which facilitates mineralization of carbazole to intermediates of the TCA cycle. Proteobacteria and Actinobacteria are the predominant bacterial phyla implicated in this novel mode of dioxygenation, while anthranilic acid and catechol are the signature metabolites. Several studies have elucidated the degradative genes involved, the diversity of the car gene clusters and the unique organization of the car gene clusters in marine carbazole degraders. However, there is paucity of information regarding the environmental fate as well as industrial and medical importance of carbazole and its derivatives. In this review, attempt is made to harness this information to present a comprehensive outlook that not only focuses on carbazole biodegradation pathways, but also on its environmental fate as well as medical and industrial importance of carbazole and its derivatives.