Abstract
BackgroundThis study was carried out to isolate and characterize the bacterial strains from lindane-contaminated soil and they were also assessed for their lindane-degrading potential.MethodsIn this study the enrichment culture method was used for isolation of lindane degrading bacterial isolates, in which the mineral salt medium (MSM) supplemented with different concentrations of lindane was used. Further, the screening for the potential lindane degrading isolates was done using the spray plate method and colorimetric dechlorinase enzyme assay. The selected isolates were also studied for their growth response under varying range of temperature, pH, and NaCl. The finally selected isolates DAB-1Y and DAB-1W showing best lindane degradation activity was further subjected to biochemical characterization, microscopy, degradation/kinetic study, and 16S rDNA sequencing. The strain identification were performed using the biochemical characterization, microscopy and the species identifies by 16S rDNA sequence of the two isolates using the standard 16S primers, the 16 S rRNA partial sequence was analyzed through BLAST analysis and phylogenetic tree was generated based on UGPMA clustering method using MEGA7 software. This shows the phylogenetic relationship with the related strains. The two isolates of this study were finally characterized as Kocuria sp. DAB-1Y and Staphylococcus sp. DAB-1W, and their 16S rRNA sequence was submitted to GenBank database with accession numbers, KJ811539 and KX986577, respectively.ResultsOut of the 20 isolates, the isolates DAB-1Y and DAB-1W exhibited best lindane-degrading activity of 94 and 98%, respectively, recorded after 8 days of incubation. The optimum growth was observed at temperature 30 °C, pH 7, and 5% NaCl observed for both isolates. Of the four isomers of hexachlorocyclohexane, isomer α and γ were the fastest degrading isomers, which were degraded up to 86 and 94% by isolates DAB-1Y and up to 93 and 98% by DAB-1W, respectively, reported after 8 days incubation. Isomer β was highly recalcitrant in which maximum 35 and 32% lindane degradation was observed even after 28 days incubation by isolates, DAB-1Y and DAB-1W, respectively. At lower lindane concentrations (1–10 mg/L), specific growth rate increased with increase in lindane concentration, maximum being 0.008 and 0.006/day for DAB-1Y and DAB-1W, respectively. The 16 S rRNA partial sequence of isolate DAB-1Y showed similarity with Kocuria sp. by BLAST analysis and was named as Kocuria sp. DAB-1Y and DAB-IW with Staphylococcus sp. DAB-1W. The 16S rDNA sequence of isolate DAB-1Y and DAB-1W was submitted to online at National Centre of Biotechnology Information (NCBI) with GenBank accession numbers, KJ811539 and KX986577, respectively.ConclusionsThis study has demonstrated that Kocuria sp. DAB-1Y and Staphylococcus sp. DAB-1W were found efficient in bioremediation of gamma-HCH and can be utilized further for biodegradation of environmental contamination of lindane and can be utilized in bioremediation program.Electronic supplementary materialThe online version of this article (doi:10.1186/s40643-016-0130-8) contains supplementary material, which is available to authorized users.
Highlights
This study was carried out to isolate and characterize the bacterial strains from lindane-contaminated soil and they were assessed for their lindane-degrading potential
Toxicity and threats of environmental contamination are of great concern, and this problem can be solved through biodegradation-based approaches
The results and discussion based on their characterization are presented below based on biochemical, microscopy, degradation analysis, and molecular identification of their species based on molecular
Summary
Soil sampling, and isolation of bacterial strains The technical grade HCH isomers (α, β, γ, and δ; 99.9% pure) were purchased from Sigma-Aldrich Strain identification The selected isolates, DAB-1Y and DAB-1W, were characterized by morphological and biochemical characterization; 16S rRNA sequencing and one isolate (DAB1W) in addition to 16S rRNA were characterized by GC-FAME technique The former technique is based on the sequencing using universal primers to the 16S rDNA of our isolates and later is based on the analysis of the fatty acid profile of the bacteria. Morphological and biochemical characterization The different morphological studies of the selected lindane-degrading isolates, DAB-1Y and DAB-1Y, were carried out to determine their cell shape, cell size, color, cell motility, capsule formation, colony morphology, pigmentation etc., by growing the culture on nutrient agar plates followed by preliminary identification using Gram’s staining. The genomic expressions (i.e., DNA/ RNA homology, lipid composition, protein pattern etc.) are conserved among a group of microbial species and they seem to be the reliable indicators for the identification This analysis makes use of short chain fatty acids to characterize genera and species of bacteria. The aerobic library (RTBSA 6.21) was referred for analysis of the DAB-1W strain and was performed as per the method given by Sasser (2001)
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