Assessment of stability of the flow cytometric microbiota profile prior to formaldehyde fixation

If multiple samples for microbiota analysis are collected, storage on ice prior to formaldehyde fixation is inevitable. It has been shown that the flow-cytometric FSC/DAPI profile of bacterial communities remains stable long-term after formaldehyde fixation and storage in 70% EtOH at -20°C (REF). In this experiment, it was addressed how storage time prior to formaldehyde fixation affects the FSC/DAPI profile of fecal microbiota samples.
Conclusion:
The FSC/DAPI profile of samples remains stable for at least 3 hours prior to formaldehyde fixation. Thus, multiple samples of fecal microbiota can be collected at once and be stored on ice for at least 3 hours without affecting their FSC/DAPI profile. Fluorescent beads FluoSpheres 2 µm (505/515, Lot-Nr. 24498W, Molecular Probes Eugene, Oregon, USA), FluoSpheres 1 µm (350/440, Lot-Nr. 69A1-1, Molecular Probes Eugene, Oregon, USA), and Fluoresbrite BB Carboxylate microspheres 0.5 µm (360/407, Lot-Nr. 552744, Polyscience, USA) were used to align the instrumental settings.