How do bacteria use vision for survival and adaptation?

[Q_Goest]

From Quantum Evolution (Johnjoe McFadden)

Many microbes, including photosynthetic bacteria, possesses the most rudimentary vision. These bacteria are able to swim towards bright light where their photosynthetic skills are most effectively deployed. They even have colour vision since they are able to concentrate where in the spectrum their chlorophyll absorbs the most light. Mutants can be isolated that lack this phototactic ability, demonstrating that the gene for some kind of photoreceptor is encoded in their DNA and thereby subject to mutation and natural selection.

1. What biological feature of a bacteria allows it to 'see' or detect a given wavelength of light? What part of or feature of the cell detects light of a given wavelength?

2. Are these not single celled organisms?

3. How common is this feature?

 

[selfAdjoint]

From Quantum Evolution (Johnjoe McFadden)

1. What biological feature of a bacteria allows it to 'see' or detect a given wavelength of light? What part of or feature of the cell detects light of a given wavelength?

Spots of opsin chemical (what we have in our retinas) on or just under the cell surface, combined with some transpot mechanism (not nerves) to get the info that a set of molecules has tripped due to being exposed to light to the motive mechanism of the bacterium.

2. Are these not single celled organisms?

Yup. Sure stretches your preconceptions about "single celled" doesn't it?

3. How common is this feature?

Not at all uncommon. There are far more bacteria, and KINDS of bacteria, than there are animals big enough for humans to see. Just, literally, a whole world of life there. What they need to have in their vraious niches is what they have evolved to have. Evolution didn't stop when chordates branced off.

(Added later:) See this excellent discussion of the variety of eyes and other visual mechalisms in the animal kingdom. http://scienceblogs.com/pharyngula/2006/11/the_eye_as_a_contingent_divers.php

 

[Q_Goest]

Thanks Self. So ospin is a family of molecules which react to light, and these molecules are encoded by DNA. I assume the DNA actually has a section of it's length dedicated to making this molecule. Is the section of DNA that is responsible for encoding ospin identical to ospin? That is, could one cut out (or identify) a section of DNA which is identical to these ospin molecules?

I suppose the ospin molecule has electrons in one or more of it's atoms that responds to a photon of light with a specific wavelength. When this electron responds, it must do so by changing energy levels. Is this how ospin molecules detect light, or is there another mechanism internal to the molecule which I'm missing?

Once this mechanism within the ospin is 'triggered', I'm wondering how that change in the ospin can be relayed to other parts of the cell. From the article you posted, it sounds like there are two mechanisms, cilary photodetection and rhabdomeric photodetection.

In the course of evolution, vertebrate vision favored ciliary photodetection for the pathway that delivers images, whereas invertebrates favored rhabdomeric photodetection for their main eyes, although why this might be remains unknown.

Can you elaborate?

 

[selfAdjoint]

Thanks Self. So ospin is a family of molecules which react to light, and these molecules are encoded by DNA. I assume the DNA actually has a section of it's length dedicated to making this molecule. Is the section of DNA that is responsible for encoding ospin identical to ospin? That is, could one cut out (or identify) a section of DNA which is identical to these ospin molecules?

First of all, that's opsin, as "ops-in", sort of "eye-chemical". No the DNA is not identical to the opsin. look up the Genetic Code. DNA makes RNA and RNA makes proteins, is the basic mechanism. I don't know if they've identified the piece of DNA that codes for opsin.

I suppose the ospin molecule has electrons in one or more of it's atoms that responds to a photon of light with a specific wavelength. When this electron responds, it must do so by changing energy levels. Is this how ospin molecules detect light, or is there another mechanism internal to the molecule which I'm missing?

This is right. And then when the electron goes into the higher energy level it causes the whole molecule to flex; to actually bend or twist. In our visual systems this causes impulses to be sent down our optic nerve to our visual cortex - at the back of our brains - where they are processed into the "vision" that we experience.

Once this mechanism within the ospin is 'triggered', I'm wondering how that change in the ospin can be relayed to other parts of the cell. From the article you posted, it sounds like there are two mechanisms, cilary photodetection and rhabdomeric photodetection.

Can you elaborate?

I dpn't know how the cell does it, but I'm sure the scientists who study these bacteria do. It should be possible to find some description somewhere.

 

[Q_Goest]

Humans cannot make Rhodopsin, instead they use and external source, -carotene, that is found in food in order to synthesis it:

Looks like http://www.chm.bris.ac.uk/webprojects2003/rogers/998/Rhoeye.htm" says Rhodopsin is not made by our DNA, but is synthesized by our body. I'd guess that other opsin molecules are similarly made by our body. I had thought that perhaps such a molecule was encoded by DNA but I suppose that's not true from reading this.

I found a neat animation on the net here:
http://www.blackwellpublishing.com/matthews/rhodopsin.html
showing a photon incident on the rhodopsin and the resulting bending or twisting you referred to. (Click the light switch in the lower left hand corner of the animation on the second page.)

I'd still be interested in how that mechanism results in a signal that can be transmitted to the locomotion parts of the bacteria.

Sure stretches your preconceptions about "single celled" doesn't it?

Yup.

 

[iansmith]

Looks like http://www.chm.bris.ac.uk/webprojects2003/rogers/998/Rhoeye.htm" says Rhodopsin is not made by our DNA, but is synthesized by our body. I'd guess that other opsin molecules are similarly made by our body. I had thought that perhaps such a molecule was encoded by DNA but I suppose that's not true from reading this.

the enzyme that play a role in synthesize the molecule might be encoded in the genome. Unless, it's a protein it will not be encoded. A complex enzymatic pathway is often needed in order to synthesize molecule from precursors.

I'd still be interested in how that mechanism results in a signal that can be transmitted to the locomotion parts of the bacteria.

Probably through phosphorylation of sensor or DNA binding proteins. Bacteria are capable of sensing internal signals through protein/protein interaction which often results in the phosphorylation of the target protein. The phosphorylated protein loses affinity toward its partner but gains affinity toward a different molecules/partner. This might cause a chain reaction.

The same type of signal transduction is also present in eukaryotic.

You might be interested in the following paper:
http://www.ncbi.nlm.nih.gov/entrez/...t_uids=8901623&query_hl=3&itool=pubmed_docsum

 

[quasi426]

Also remember the size of bacteria and the cost benefits of seeing with vision. Many of the bacteria's inputs of the outside environement are through channels and receptors that lead to signal transduction cascades. That is to say that some outside stimulus can bind on a transmembrane protein known as receptors on the outer surface of the bacteria, the receptor will cause internal chemical reactions that lead to more internal chemical reactions that will finally lead to a change in concentration of a messenger molecule. The messenger molecule's concentration can control DNA expression which can lead to metabolic changes that may be required such as degrading a toxin, or internalizing and metabolizing energy source.