When settling samples containing Dolichospermum preserved in Lugol's acid, we are having an issue with filaments gravitating toward the sides of the settling chamber while other organisms seem to settle out normally. Is this an issue with the buoyancy of Dolichospermum? Would additonal Lugol's help at all?
Thanks,
Ben
From Nollet & Gelder (2014) "Handbook of Water Analysis" pg. 148.
"Species of cyanobacteria containing gas vesicles may not settle fully despite the addition of lugol's iodine; therefore, the gas vesicles need to be collapsed before the sample is set up for sedimentation."
My assumption is that the Dolichospermum sp. you are analyzing is maintaining some amount of gas vesicle content after preservation, and that curvature of the meniscus of the settling chamber is forcing these partially buoyant cells towards the exterior of the settling chamber, where they may, or may not, then settle. I have had issues with this previously, and it is more pronounced when using gluteraldehyde preserved samples.
Thanks Stuart Dyer! I knew you'd be the guy to ask. It's so weird bc the filaments will appear to spread homogeneously in the chamber upon initial settling (a few hours after filling the chamber when we screen for density), then spread out to the edges when we leave it overnight to settle completely. Is there a simple technique for collapsing the gas vesicles?
Happy to help! Claudia E. Tausz I would use a luer lock syringe large enough to accommodate your sample and an additional ~1-2 mL of air space. Just load the sample+air, secure the cap on the tip of the syringe, and, with the tip supported, give the plunger a good whack with a mallet; the sudden rapid increase in pressure should be enough to collapse the majority of the gas vesicles. I've also come across people recommending the use of PTFE (teflon) towers, as they largely remove the curvature of the meniscus.
- Badges
- Science topic
- Similar topics
- Chemistry
- Sulfites
- Inorganic Chemistry
- Acids