A simple method to preserve oceanic phytoplankton for flow cytometric analyses

Area of Science:

• Marine Biology
• Oceanography
• Microscopy

Background:

• Flow cytometry is crucial for analyzing marine phytoplankton populations.
• Timely analysis of phytoplankton is often limited by logistical constraints.
• Effective preservation methods are needed to overcome these limitations.

Purpose of the Study:

• To develop and validate a simple method for preserving marine phytoplankton samples.
• To enable delayed flow cytometric analysis of phytoplankton.
• To assess the impact of the preservation method on cell integrity and fluorescence properties.

Main Methods:

• Marine phytoplankton samples (individual species and natural populations) were fixed with 1% glutaraldehyde.
• Fixed samples were stored in liquid nitrogen for delayed analysis.
• Preservation effectiveness was evaluated by cell loss, forward angle light scatter, and chlorophyll and phycoerythrin fluorescence.

Main Results:

• The glutaraldehyde fixation and liquid nitrogen storage method generally preserved phytoplankton populations with minimal cell loss.
• Forward angle light scatter and chlorophyll fluorescence were well-preserved across most samples.
• Phycoerythrin fluorescence showed increased intensity in some cases.
• The method was highly effective for small picoplankton (e.g., Synechococcus, prochlorophytes).
• Preservation was less effective for fragile, larger cells like dinoflagellates and cryptophytes.

Conclusions:

• Immediate fixation with glutaraldehyde followed by liquid nitrogen storage is a viable method for preserving marine phytoplankton for flow cytometry.
• This technique is particularly suitable for analyzing small picoplankton.
• Careful consideration and case-by-case application are necessary for preserving larger or more fragile phytoplankton species.