Limits of propidium iodide as a cell viability indicator for environmental bacteria.
BACKGROUND
Viability measurements of individual bacteria are applied in various scopes of research and industry using approaches where propidium iodide (PI) serves as dead cell indicator. The reliability of PI uptake as a cell viability indicator for dead (PI permeable) and viable (PI impermeable) bacteria was tested using two soil bacteria, the gram(-) Sphingomonas sp. LB126 and the gram(+) Mycobacterium frederiksbergense LB501T.


METHODS
Bacterial proliferation activities observed viaDAPI and Hoechst 33342 staining were linked to the energy charge and the proportion of dead cells as obtained by diOC(6) (3)-staining and PI-uptake, respectively. Calibration and verification experiments were performed using batch cultures grown on different substrates.


RESULTS
PI uptake depended on the physiological state of the bacterial cells. Unexpectedly, up to 40% of both strains were stained by PI during early exponential growth on glucose when compared to 2-5% of cells in the early stationary phase of growth.


CONCLUSIONS
The results question the utility of PI as a universal indicator for the viability of (environmental) bacteria. It rather appears that in addition to nonviable cells, PI also stains growing cells of Sphingomonas sp. and M. frederiksbergense during a short period of their life cycle.
Shi
Lei
L
Department of Environmental Microbiology, UFZ, Helmholtz Centre for Environmental Research, Leipzig-Halle, 04318 Leipzig, Germany.
Günther
Susanne
S
Hübschmann
Thomas
T
Wick
Lukas Y
LY
Harms
Hauke
H
Müller
Susann
S
D001562:Benzimidazoles / Q000378:metabolism; D002138:Calibration; D002232:Carbocyanines / Q000378:metabolism; D004783:Environmental Microbiology; D004926:Escherichia coli / Q000254:growth & development; D007211:Indoles / Q000378:metabolism; D050296:Microbial Viability; D009161:Mycobacterium / Q000166:cytology* / Q000254:growth & development; D011419:Propidium / Q000032:analysis* / Q000378:metabolism*; D015203:Reproducibility of Results; D020578:Sphingomonas / Q000166:cytology* / Q000254:growth & development; D013194:Staining and Labeling; D013997:Time Factors
D001562:Benzimidazoles; D002232:Carbocyanines; D007211:Indoles; D011419:Propidium; C007293:DAPI; C007392:3,3'-dihexyl-2,2'-oxacarbocyanine; C017807:bisbenzimide ethoxide trihydrochloride