Bacterial behaviour.

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apochronaut
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Bacterial behaviour.

#1 Post by apochronaut » Fri Sep 18, 2020 2:35 am

Increasinhly I find myself more interested in the behaviour of micro-organisms than the splendour of their structure. It is difficult to imagine cognizance in such tiny bodies yet here I relate two recent phenomena.
Part of my microscopy involves a frequent return to certain creeks, with an eye to look for changes. It's a long project..

Some samples from the spring were reviewed at the time and then set aside. Sometimes I return the samples and sometimes if there is something of interest I keep it, replenishing it with water and sometimes nutrient. One spring sample had a species of 35 micron amoeba that I was interested in looking at further with higher resolution DF and or phase at 13 or 1400X.
I didn't get to it until recently. One thing I found was that the population of bacteria had swelled, with an increased proportion if them being gliding bacteria. There is lots of motility in the sample. My initial observation was with Bright M phase, which reveals small organisms as brilliant white on a grey background. After a period of viewing at 430X, I went back to 100X in order to orient myself better and noticed a bright white band across the slide. It resembled the milky way across the field. Going to a higher magnification revealed that a group of about 10 species of bacteria were concentrating in a 50 micron band, which went most of the way across the sample, for thousands of microns. The organisms ranged from 1/2 micron to 10 or so and I counted 9 individual species. I observed the anomaly for a while then returned it to it's jar. A day later , when observing a drop from the same sample, the same thing happened. After about 15 minutes, an approximately 50 micron concentrated band of bacteria develops. The third time I witnessed it, it described a complete circle about 4000 microns in diameter. Usually , it is a line though and it can be quite straight. Organisms will stray from the band out about 50 microns either way but usually return to the area of concentration. Every time I take a sample, the same thing happens and it seems to have organization.
Has anyone else experienced this kind of behaviour? It seems that it might be a response to light.

The high concentration of organisms creates a dense wall. The sample also has a high population of gliding bacteria, some of which move in an undulating fashion, almost a wave form. The undulation is quite consistent and seems to require a certain amplitude to drive the creature forward. While none if these larger 60 or so micron bacteria show any tendency to contribute to the wall, they do show a desire to pass through it, initially without success. They are persistent, though. This results in one of the most interesting behaviours I have witnessed through a microscope. The heavy concentration of bodies restricts the ability of the undulating bacteria to penetrate the wall, I am guessing due to a restriction in amplitude. They can however reverse and their response is to back out and try again and again, and each time they try to pass through the same area the body concentration restricts the undulation sufficiently that forward motion ceases, when they are about 1/2 way through. Here is where it gets interesting. The gliding bacteria, will back out yet again and change the angle of approach to the bacterial wall, therefore passing through a different portion. If that doesn't work, it does it again and eventually it finds a passage sufficiently open enough that it can pass through. I have witnessed this change of angle technique dozens of times.
This certanly shows something other than an automatic programmed response.

Hobbyst46
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Re: Bacterial behaviour.

#2 Post by Hobbyst46 » Fri Sep 18, 2020 10:25 am

This seems to be a very interesting and intriguing topic !
Please elaborate on the dimensions. The 0.5 um to 10 or 60 um ? are all of them bacteria ?

Perhaps one way to investigate them is under DF, if they scatter intensely, then time-lapse and/or video photography, then image analysis can tell about the percentage of cooperation of motion, i.e. do they move as group, the track, etc. Such studies are being performed on live cells and small organisms (ants...).

And the "invasive" or "crossing" organisms... Could they move without gliding, i. e. "swim", the bacterial film would not be an obstacle, since the depth of the channel is probably of the order of 100 um (?).
Zeiss Standard GFL+Canon EOS-M10, Olympus VMZ stereo

apochronaut
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Re: Bacterial behaviour.

#3 Post by apochronaut » Fri Sep 18, 2020 12:08 pm

The gliding bacteria is most likely a species of flavobacteria. It moves at about 10 um/sec., probably faster mostly.

It is hard to detect but there may be a type of corkscrew motion associated with the undulating or swimming motion. The thing is, due to it's small diameter of only about 2 um, unlike large ciliates,it can penetrate the dense wall formed by these congregating bacteria but they repeatedly get lodged about 1/2 way through. They try again and try again, each time knowing to back out , usualiy about 50 microns from the wall. At some point they "know" to change the angle of approach, eventually finding a less dense area that they can pass through and on their way in the same direction they had originally chosen. Ciliates seem to just bounce off the wall and change direction, somewhat purposeless. The flavobacteria, seem to have a purpose and a crude form of problem solving. It may be chemically mediated but on that basis, one could probably devise an experiment that could get them to solve a maze.

Hobbyst46
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Re: Bacterial behaviour.

#4 Post by Hobbyst46 » Fri Sep 18, 2020 12:54 pm

apochronaut wrote:
Fri Sep 18, 2020 12:08 pm
The gliding bacteria is most likely a species of flavobacteria. It moves at about 10 um/sec., probably faster mostly.

It is hard to detect but there may be a type of corkscrew motion associated with the undulating or swimming motion. The thing is, due to it's small diameter of only about 2 um, unlike large ciliates,it can penetrate the dense wall formed by these congregating bacteria but they repeatedly get lodged about 1/2 way through. They try again and try again, each time knowing to back out , usualiy about 50 microns from the wall. At some point they "know" to change the angle of approach, eventually finding a less dense area that they can pass through and on their way in the same direction they had originally chosen. Ciliates seem to just bounce off the wall and change direction, somewhat purposeless. The flavobacteria, seem to have a purpose and a crude form of problem solving. It may be chemically mediated but on that basis, one could probably devise an experiment that could get them to solve a maze.
About a year ago, intelligent behavior - memory, learning etc - was re-discovered in a specific species of Stentors. Individual behavior, somewhat similar to this description.
Zeiss Standard GFL+Canon EOS-M10, Olympus VMZ stereo

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Rossf
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Re: Bacterial behaviour.

#5 Post by Rossf » Fri Sep 18, 2020 1:19 pm

I’m in the same boat Apochronaut-My favourite microscopic pastime is keeping a Petri dish sample for 2-3 days to see the changes develop-who’s eating who-fungi spores sprouting and like you said the interaction between microbes-I also add a bit of food-maybe a tiny bit of maple syrup or similar.thats where inverted scopes really show they are a completely different beast-and I like as low N/A as I can get-don’t want super detail-want to make out the full shape of the microbe rather than thin slices-keep exploring! My fav 40x’s for inverted is this Olympus low N/A monster below-huge front element and a Leica 40x n/a .50
Sharpness isn’t everything in microscopy IMO.
Regards ross
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hans
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Re: Bacterial behaviour.

#6 Post by hans » Tue Sep 22, 2020 6:50 am

Are bacteria able to mechanically detect a lack of forward progress, to trigger the "backing out" behavior? Or would they be sensing something else, like some chemical difference near/within the wall?

apochronaut
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Re: Bacterial behaviour.

#7 Post by apochronaut » Tue Sep 22, 2020 6:20 pm

I can and will recreate the conditions underwhich that particular obstacle negotiating behaviour took place, as long as I am able to maintain that creek sample fairly stable. At that time I will probably video it ; if all goes well.
Gliding bacteria are one of my favourite subjects. They seem to be more prevalent at least around here, than they used to be. Their locomotive capability is of interest to various researchers and there have been some interesting papers written covering various aspects of it.
7
The multiple observations I made of this peculiar behaviour did not give me the impression that chemical cues were much of a factor. It seemed more to be a response to restrictions placed on locomotive mechanisms by the density of the bacterial concentration in the 50 micron thick wall. Since the motile flavobacteria seem highly motivated to change their location and those members of the genus likely encounter unknown barriers, obstacles and areas of compression commonly, the ability to recognize and reverse out of a physical trap is no doubt genetically encoded as a necessary survival mechanism. It was the deliberate alteration in the angle of approach, after several attempts to ramrod through the same location that was so remarkable. I can't quite see how that would have been a response to chemical markers. I am used to seeing fairly motile species, protists mostly, exhibit more random and less seemingly deliberate directional choices.

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