Stephanodiscus (ID ??) and Friends Close Up

Images made through a microscope. All subject types.

Moderators: rjlittlefield, ChrisR, Chris S., Pau

discomorphella
Posts: 607
Joined: Sun Oct 01, 2006 7:26 pm
Location: NW USA

Stephanodiscus (ID ??) and Friends Close Up

Post by discomorphella »

Hey, how do you like my new DIC setup? Nice neutral gray color, eh? Ok, joking aside, I figured you guys would like to see a really close-up view of some diatoms.
As part of our work site's open house, we decided to show some microscopic views of everyday objects. Diatoms are always underfoot, even if nobody realizes it (except for the readers of photomacrography.net of course). The scopes are of course pretty heavily subscribed, so I don't get to do this very often, but for the open house we made an exception. I walked out to a nearby pond and collected a few ml of bottom material. Not having a lot of time to formally process it, I tried the following quick sample prep method;
Spread goo onto an APTES-treated coverslip, fixed it in acetone, vacuum dried it then sputtered a thin (<1000 A typically) layer of Au/Pd over it and stuck the coverglass onto a "carbon dot" and put it into the SEM on a standard mounting "stub"...
The gold / palladium coating is to provide some conduction path from the glass (diatoms and the coverslip) to the grounded sample holder. If there's not some return path your sample charges up, and starts repelling the electrons, wiping out the image of your sample.
The SEM cognoscenti out there will realize that these images are not nearly as good as I could have gotten, you'll note that my working distance is huge, while the accelerating voltage is quite low. That's because I didn't want to charge up my pond scum and have it fly all over the inside of the SEM chamber; it would have been VERY obvious who had filthed up the SEM (not too many other people look at samples from ponds in my lab).

One thing I was struck by, not being a diatomist, is just how much variation exists in the pore size and morphology. Additionally, in the 2nd and 3rd images, you can see an interior set of smaller (approximately 20 nm or so) openings inside each pore. The interior "holes" show up faintly, since I was keeping the sample very far away from the bottom lens and using pretty weak accelerating voltage lowering the SEM's ultimate resolution. I think these could be pores in the diatom's cell wall (or a processing artifact).
I have guessed at the genus for the centric diatom in the first 3 images. The ID of the larger diatom (fragment) in the next 3 images is still a mystery to me. Note the elaborate interior details of the pores. As always, please correct my taxonomic guesswork, I'm a p-chemist, not a diatomist...

David

Image
Image
Image
Image
Image
Image

Mitch640
Posts: 2137
Joined: Sun Aug 15, 2010 1:43 pm

Post by Mitch640 »

Very interesting. #4 looks like wreckage of the kitchen, on the Titanic. :)

BJ
Posts: 355
Joined: Sat Sep 29, 2007 10:53 am
Location: England

Post by BJ »

hi David,

great to see some SEM ....you must sneak some more time on the instrument !

I would agree with you on Stephanodiscus for the centric diatom, but I have no idea of the species.

I have a theory on the large fragment. I think that it represents one quarter of a valve of an asymmetric naviculoid diatom eg a species of Cymbella. The valve has broken across the short axis and has also cracked along the raphe (the raphe lying along the lower edge of the fragment in your photo).

You could compare the pore pattern in your specimen with this:

http://www.astrographics.com/GalleryPri ... P2122.html

You must take some more photos...if you wreck the mike ...just blame me!!

thanks for posting
boa sorte
Brian

discomorphella
Posts: 607
Joined: Sun Oct 01, 2006 7:26 pm
Location: NW USA

Post by discomorphella »

Thanks Brian--

I'll try explaining to the SEM's owner that these were special SiO2 micromachined structures that were part of a photochemical energy production machine. Which they are in a sense. I'll post some more from the "goop slide", as I did grab a few more shots of other diatoms. Next time I'll try to spend a bit more time cleaning and centrifuging the bottom material so I have cleaner diatom preps. Mitch is correct about the 4th image looking like a train wreck in a diatom factory. In addition to the large fragment, I can see at least 4 other diatoms and bits, along with what could be the shattered remnants of a loricate euglena laying in the lower right corner. I am still amazed at how irregular the pores are compared to the more uniform appearance they take on in our more blurred optical photos.

David

rjlittlefield
Site Admin
Posts: 23501
Joined: Tue Aug 01, 2006 8:34 am
Location: Richland, Washington State, USA
Contact:

Post by rjlittlefield »

discomorphella wrote:I am still amazed at how irregular the pores are compared to the more uniform appearance they take on in our more blurred optical photos.
We humans read a lot between the lines. The array is regular, so the components must be regular too, right? And it's true, one dark blob looks very much like the next as long as the sizes are similar! :)

Thanks for the SEM images. They make a great complement to all the optical stuff!

--Rik

Charles Krebs
Posts: 5865
Joined: Tue Aug 01, 2006 8:02 pm
Location: Issaquah, WA USA
Contact:

Post by Charles Krebs »

David,

SEM images are always amazing to look over. Frustrating as well to us "light" microscopists. One reason to concentrate on live subjects, and subjects where natural color is an important aesthetic or informational consideration I suppose (and leave the pollen grains and diatom frustules to the folks who play with electrons).

Really nice to see. Thanks for posting.

discomorphella
Posts: 607
Joined: Sun Oct 01, 2006 7:26 pm
Location: NW USA

Post by discomorphella »

You are all most welcome. I have a few more diatoms that were decently presented on the "goop sample" and as soon as I have a few moments to retrieve them, compress etc I'll post them. I'll include some measurements of the pores and their spacing so we'll all have some natural calibration targets, although these diatoms are not exactly adhering to NIST-traceable standards considering how much their pores vary. As Rik pointed out, my brain had idealized them into identically sized structures when observed through a light microscope. Looking at the pores on the Stephanodiscus, almost all are substantially less than the spot size for even a 1.4 NA objective with 550 nm (the usual green) light, so they will all be blurred to the final MTF-determined spot size (full width at half-max approximately 0.3 microns, more or less, on a good day for the scope and the sample...) when viewed through our optical scopes.
I'll have to make another lunch-time run to the pond and then get the sample holder a lot closer and crank up the Vacc and see how sharp an image we can get of those Cymbella pores. Anyone have any ideas about what function those elaborate structures inside the pores could have?

David

BJ
Posts: 355
Joined: Sat Sep 29, 2007 10:53 am
Location: England

Post by BJ »

David,

you may find this article interesting...you can download it as a pdf for free and look as well at the supplementary data:

http://www.ingentaconnect.com/content/b ... 3/art00006

supplementary data:

http://www.ingentaconnect.com/content/b ... ta/sd00015

I imagine myself, that a large pore may be large enough to permit entry of some pathogens, whilst the smaller openings may give dramatically improved protection. Another issue might be the cell membrane and protoplasm bulging out through the larger pore without the finer support.

I suspect that the overall structure will be optimised for strength with minimal weight / cost of construction.

Maybe, then again, it is just the current fashion amongst diatoms...come back in another 100 million years and all change...mini pores are out and flares are back.

tchau
Brian

discomorphella
Posts: 607
Joined: Sun Oct 01, 2006 7:26 pm
Location: NW USA

Post by discomorphella »

Wow, thanks Brian. That is way cool. P-chem and diatoms combined. My lunchtime reading. Thanks again,

David

Post Reply Previous topicNext topic