Impact of fluorochrome stains used to study bacterial transport in shallow aquifers on motility and chemotaxis of Pseudomonas species

Abstract

One of the most common methods of tracking movement of bacteria in groundwater environments involves a priori fluorescent staining. A major concern in using these stains to label bacteria in subsurface injection‐and‐recovery studies is the effect they may have on the bacterium's transport properties. Previous studies investigated the impact of fluorophores on bacterial surface properties (e.g. zeta potential). However, no previous study has looked at the impact of fluorescent staining on swimming speed and chemotaxis. It was found that DAPI lowered the mean population swimming speed of Pseudomonas putida F1 by 46% and Pseudomonas stutzeri by 55%. DAPI also inhibited the chemotaxis in both strains. The swimming speeds of P. putida F1 and P. stutzeri were diminished slightly by CFDA/SE, but not to a statistically significant extent. CFDA/SE had no effect on chemotaxis of either strain to acetate. SYBR® Gold had no effect on swimming speed or the chemotactic response to acetate for either strain. This research indicates that although DAPI may not affect sorption to grain surfaces, it adversely affects other potentially important transport properties such as swimming and chemotaxis. Consequently, bacterial transport studies conducted using DAPI are biased to nonchemotactic conditions and do not appear to be suitable for monitoring the effect of chemotaxis on bacterial transport in shallow aquifers.

Chemotaxis Increases the Residence Time of Bacteria in Granular Media Containing Distributed Contaminant Sources

“…The values listed in Table S8 agree with literature values. 9,[13][14][15][16] Figure S3 also shows a plot of FSC-H versus FSC-A obtained from the flow cytometer. Cells with a larger size have a higher FSC-H and FSC-A, as seen with the PpG7 Y1 strain.…”

Methods to Evaluate Bacterial Motility and Its Role in Bacterial–Host Interactions

“…Exogenous labels, such as fluorescent probes, can be simpler to apply but will be diluted as bacteria divide, and one must be aware that they can potentially alter bacterial function. Staining with DAPI, for example, halves the swimming speed of Pseudomonas species [ 49 ], and fusions of fluorescent proteins to components of the bacterial flagellar motor can alter its dynamics [ 50 ].…”

Transverse Migration of Chemotactic Bacteria Toward Chemical Attractants in a Two Dimensional Microcosm with Converctive Flow

“…A different color stain would be required to distinguish between types of bacteria, as well as microscopes capable of distinguishing between the two colors. A major concern when using bacteria stains is that the stains often reduce motility of the bacteria (Toepfer et al 2012). Chemotactic bacteria labeled with green fluorescent protein and nonchemotactic bacteria labeled with red fluorescent protein would be a possible combination.…”

“…Simultaneous injection of chemotactic and nonchemotactic bacteria was not performed in this study because the green fluorescent protein labeled chemotactic bacteria exhibited low fluorescence which made it difficult to accurately count all chemotactic bacteria. DAPI staining is an option for the nonchemotactic bacteria, but not for the chemotactic bacteria, because it impairs chemotaxis and the motility of chemotactic bacteria (Toepfer et al 2012). DAPI stained nonchemotactic bacteria could be injected with unlabeled chemotactic bacteria, however there is not yet an effective way to count the chemotactic bacteria in the effluent sample.…”