An approach to increase the success rate of cultivation of soil bacteria based on fluorescence-activated cell sorting

PLoS One. 2020 Aug 31;15(8):e0237748. doi: 10.1371/journal.pone.0237748. eCollection 2020.

Abstract

Soil microbiota are considered a source of undiscovered bioactive compounds, yet cultivation of most bacteria within a sample remains generally unsuccessful. Two main reasons behind the unculturability of bacteria are the presence of cells in a viable but not culturable state (such as dormant cells) and the failure to provide the necessary growth requirements in vitro (leading to the classification of some bacterial taxa as yet-to-be-cultured). The present work focuses on the development of a single procedure that helps distinguish between both phenomena of unculturability based on viability staining coupled with flow cytometry and fluorescence-activated cell sorting. In the selected soil sample, the success rate of cultured bacteria was doubled by selecting viable and metabolically active bacteria. It was determined that most of the uncultured fraction was not dormant or dead but likely required different growth conditions. It was also determined that the staining process introduced changes in the taxonomic composition of the outgrown bacterial biomass, which should be considered for further developments. This research shows the potential of flow cytometry and fluorescence-activated cell sorting applied to soil samples to improve the success rate of bacterial cultivation by estimating the proportion of dormant and yet-to-be-cultured bacteria and by directly excluding dormant cells from being inoculated into growth media.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacteria / chemistry
  • Bacteria / genetics
  • Bacteria / growth & development*
  • Biomass
  • Cell Separation / methods
  • Culture Media
  • DNA, Bacterial / isolation & purification
  • Feasibility Studies
  • Flow Cytometry / methods
  • Fluorescent Dyes / chemistry
  • Microbiological Techniques / methods*
  • Microbiota / physiology*
  • Phylogeny
  • RNA, Ribosomal, 16S / genetics
  • Sequence Analysis, DNA
  • Soil Microbiology*
  • Staining and Labeling / methods

Substances

  • Culture Media
  • DNA, Bacterial
  • Fluorescent Dyes
  • RNA, Ribosomal, 16S

Grants and funding

L.E. was able to carry out this investigation thanks to the funding provided by the Knowledge Transfer Partnership programme from Innovate UK (project number 509858 and partnership number 10315, http://ktp.innovateuk.org). The KTP programme involved an academic partner (Cardiff University, represented by Prof. Tim Walsh) and a business partner (Neem Biotech Ltd., company number 03609233). Innovate UK covered for 67% of the costs associated with the present work (salary for L.E., consumables, travel costs and training costs), and Neem Biotech funded the remaining 33%. Neither funder had any role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of the author are articulated in the “author contributions” section.