River diatoms and "bubbles"
Posted: Fri Apr 10, 2020 10:59 pm
Hi All,
Health and safety to everyone.
A week before the corona lock-down I collected a live diatom sample from a small polluted local river. As expected, most diatoms were pennales and the variability was poor. Nevertheless, I cleaned them with APS* and home-grade hypochlorite, and managed to prepare a few Pleurax strew slides. In spite of my sloppy preparation and plenty of debris, diatoms could be clearly observed. I inspected them with the following objectives : 40X/0.75 phase contrast (PC) dry, 40X/0.8 (iris) oil darkfield (DF), 100X/1.3 Planapo PC (oil), 100X/1.25 achromat (oil) sort-of-DF. The ultracondenser (oil) was used for DF. Images were taken with the afocally-installed mirrorless, except for DF which were taken with an eyepiece camera.
I always start a diatom session by phase contrast; at 40X or 100X PC it is fun (see photo 1 for an example), and well worth the trouble of the oil immersion. Diatom lengths were mostly 15-50 um. Due to the gentle cleaning, many diatoms remained fairly intact (photos 2 & 3), although some were broken into valves and girdles. Diatoms that appear much brighter and more colorful than others are, I believe, intact frustules. Others might be just valves. Photo 2 shows two diatoms (Naviculas?), that are mutually aligned, perhaps owing to the shape of their outer surfaces, or maybe they are actually a single "thick" frustule ??
I noticed a circle, an air bubble - what else could it be? (Photo 4, PC). Then another circle appeared (photo 5, DF), and another. Strangely enough, they are all about the same diameter - 15-20 um. Such uniform air bubbles?. Switched the slide for another and tried BF with the 40X dry (photo 6, middle). Now that is not a bubble, but a short transparent open tube. Tried oblique (photo 7) - it is a transparent shallow cylindrical container. And the same conclusion from another (photo 8, BF). Later, I found one that was lying on its side (photo 9, DF). And, just very few so far, I found the valve (perhaps still part of the intact frustule) of Cyclotella meneghiniana Kutzing**.
* APS cleaning is less hazardous than many literature procedures, but appropriate precautions and laboratory safety measures are mandatory.
** Identification is based on an atlas of local diatoms.
So, several illumination modes can help to answer a question.
Comments are welcome.
Health and safety to everyone.
A week before the corona lock-down I collected a live diatom sample from a small polluted local river. As expected, most diatoms were pennales and the variability was poor. Nevertheless, I cleaned them with APS* and home-grade hypochlorite, and managed to prepare a few Pleurax strew slides. In spite of my sloppy preparation and plenty of debris, diatoms could be clearly observed. I inspected them with the following objectives : 40X/0.75 phase contrast (PC) dry, 40X/0.8 (iris) oil darkfield (DF), 100X/1.3 Planapo PC (oil), 100X/1.25 achromat (oil) sort-of-DF. The ultracondenser (oil) was used for DF. Images were taken with the afocally-installed mirrorless, except for DF which were taken with an eyepiece camera.
I always start a diatom session by phase contrast; at 40X or 100X PC it is fun (see photo 1 for an example), and well worth the trouble of the oil immersion. Diatom lengths were mostly 15-50 um. Due to the gentle cleaning, many diatoms remained fairly intact (photos 2 & 3), although some were broken into valves and girdles. Diatoms that appear much brighter and more colorful than others are, I believe, intact frustules. Others might be just valves. Photo 2 shows two diatoms (Naviculas?), that are mutually aligned, perhaps owing to the shape of their outer surfaces, or maybe they are actually a single "thick" frustule ??
I noticed a circle, an air bubble - what else could it be? (Photo 4, PC). Then another circle appeared (photo 5, DF), and another. Strangely enough, they are all about the same diameter - 15-20 um. Such uniform air bubbles?. Switched the slide for another and tried BF with the 40X dry (photo 6, middle). Now that is not a bubble, but a short transparent open tube. Tried oblique (photo 7) - it is a transparent shallow cylindrical container. And the same conclusion from another (photo 8, BF). Later, I found one that was lying on its side (photo 9, DF). And, just very few so far, I found the valve (perhaps still part of the intact frustule) of Cyclotella meneghiniana Kutzing**.
* APS cleaning is less hazardous than many literature procedures, but appropriate precautions and laboratory safety measures are mandatory.
** Identification is based on an atlas of local diatoms.
So, several illumination modes can help to answer a question.
Comments are welcome.
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