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Isolation of high molecular weight and humic acid-free metagenomic DNA from lignocellulose-rich samples compatible for direct fosmid cloning

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Abstract

Activity-based screening of metagenomic DNA libraries is a promising approach to fish out genes encoding novel bioactive compounds/enzymes of industrial importance. The starting point of such functional screening in fosmid vectors is isolation of high molecular weight (HMW) DNA of sufficient purity from diverse environments. Metagenomic DNA isolation protocols mostly employ mechanical cell lysis that yields fragmented DNA. Those established for HMW DNA using enzymatic lysis have not considered samples with high lignocellulose or humic acid content. Enzymes from such environments are in great demand for bioenergy, paper, and related industries. Thus, an improved method was standardized that has three key features, i.e., use of harvested microbial biomass instead of raw samples, removal of humic substances prior to cell lysis by aluminum sulfate flocculation, and enzymatic/chemical lysis of cells with a lysozyme, mutanolysin, proteinase K, and SDS cocktail followed by phenol-chloroform extraction and precipitation of DNA by polyethylene glycol and NaCl. HMW DNA (~ 40 kb) was efficiently isolated from garden and forest soils, rice straw compost, and degrading wood from a hypersaline lake. The humic acid removal efficiency across samples was 96–98%. The isolated DNA was of high quality/purity and could be successfully used in downstream applications like PCR, ligation, and fosmid cloning. In fact, the DNA was directly used without any size selection, for fosmid library preparation with 70–90% efficiency as compared to the control insert. Thus, the method could suitably be used for HMW DNA isolation for the functional screening of enzymes from diverse humic acid-/lignocellulose-rich environments.

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Acknowledgements

We would like to thank the editor and the anonymous reviewers for their suggestions. Dr. Debalina Banerjee and Sohini Banerjee are acknowledged for grammatical corrections in the final version of the manuscript.

Funding

This work was financially supported by CSIR [No. 38(1410)/15/ EMR-II)] and UGC MRP [F. No. 43-462/2014(SR)]. Abhijit Sar and Srikanta Pal are thankful to UGC-BSR and CSIR for their fellowships, respectively.

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Correspondence to Bomba Dam.

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The authors declare that they have no conflict of interests.

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This article does not contain any studies with human participants or animals.

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Sar, A., Pal, S. & Dam, B. Isolation of high molecular weight and humic acid-free metagenomic DNA from lignocellulose-rich samples compatible for direct fosmid cloning. Appl Microbiol Biotechnol 102, 6207–6219 (2018). https://doi.org/10.1007/s00253-018-9102-6

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  • DOI: https://doi.org/10.1007/s00253-018-9102-6

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