Microbe. The World of Microbes.
As a start to this discussion forum, it's good to go to the website devoted to book Microbe that inspired this weblog. This website is here.
We are starting discussions with chapter 1 of this book- The World of Microbes.
Let's get started by posting a study question for discussion in the comments thread.
Question
Bacteria range in volume over a million-fold. Discuss some of the consequences of being larger or smaller than average?
Update of question and posting with more information to assist students. 4th March 2007
Here is some extra information that can assist students understand how size has implications for available membrane surface area to service the metabolic requirement of a unit cell volume.
To understand the point of the question about size, students need to think about have the ration of surface are:cell volume changes with increase in size. SA/Vol Ratio~diameter squared/diameter cubed~inversely proportional to diameter, with similar cell shapes.
To see some consequencences raised by the biology of large bacteria you need to read about observations that have been made on Epulopiscium bacteria, usually called epulos. The paper by K D Clements and S Bullivant (1991) An unusual symbiont from the gut of surgeonfishes may be the largest known prokaryote. J Bacteriol. 1991 September; 173(17): 5359–5362 provides some good interesting insights.
Figure 1 of this paper shows how large epulos are.
J Bacteriol. 1991 September; 173(17): 5359–5362. Figure 1. Light micrograph of an Epulo. The letter C indicates a smaller, eukaryotic ciliate.
J Bacteriol. 1991 September; 173(17): 5359–5362. Figure 3. Electron micrograph of a thin section of an Epulopiscium bacterium showing concolutions to cytoplasmic membrane. Such convolutions would increase the membrane area to cell volume ratio of these large bacteria
Thus epulos have a peripheral layer of highly convoluted cytoplasmic membrane - which has been interpreted as a mechanism increase in membrane area to compensate for some surface area to volume related challenges that they face because of their large size.
Extra reading for the high achieving student:
In the links at the Microbe Chapter 1 webpage, this is worth studying several times in the course.
Labels: Diversity, physiology, prokaryotes, structure
posted by GMO Pundit at 2:44 pm
9 Comments:
If you like leave a first name and ititial in your comment
Advantages of larger volume per surface area:
More reserves of fuel & nutrients. (longer survival without nutrients or fuel).
Disadvantages of larger volume per surface area:
Need for transport within cell as diffusion rate may limit growth.
As there is less surface area from which to harvest fuel and nutrients to maintain internal volume of naturally degrading proteins, more efficient transporters and porins may be required.
Bigger target. More vulnerable to immune system and predation.
Good work:
you could also talk about advantages of larger suraface area per volumes, as most bacteria are smaller.
Can you explore that line of thinking please?
Microbe Pundit
The exchange/diffusion of molecules in and out of cells will be at a higher rate as there is more surface to a single unit of volume for smaller cells.
Yes. Smaller cells are suited to growth in solutions where nutrients are at low concentrations.
Microbe Pundit
If a bacterium smaller than average and has a high surface area: volume ratio then it has the advantage of a high metabolism (fast growth) which is likely to give them a competitive advantage over other bacteria.
However, small bacteria may have less room so to speak for enzymes, microbial adaptations etc. (of couse this also depends on other things like the size of the genome so I am not saying that this applies to all bacteria) and as a consequence may aggregate with other bacteria. This can be advantageous in terms of survival however it may limit the areas in which they can live.
If a bacterium is larger than average with a low surface area: volume ratio it is likely to be slower growing. Although this may suggest that this impacts on their ability to cause disease several slow growing bacteria (such as M.tuberculosis) are sucessful pathogens. Consequently, it may suggest that bacteria with larger volumes require more adaptations to protect them whilst they grow (i.e. protect them from antibiotics in nature or from the immune system).
I would also like to know to what extent the notion that larger = slow growing holds true. Does that mean many soil bacteria which are slow growing are also large? Surely there are many other bacterial factors (such as enzymes to break down substrates) that influence growth other than size. Similarly, what are examples of bacteria which undergo a dramatic change in size (with the exception of spore forming bacteria) during their life cycle or in response to different physiological conditions.
Good questions comments Kirsty
My comments are interspersed in your useful post reproduced Here:
PUNDIT INI CAPS: If a bacterium smaller than average and has a high surface area: volume ratio then it has the POTENTIAL a high metabolism (fast growth) which is likely to give them a POTENTIAL competitive advantage over other bacteria in the right environment.
Microbe Pundit
However, VERY small bacteria may have less room so to speak for enzymes, microbial adaptations etc. (of couse this also depends on other things like the size of the genome so I am not saying that this applies to all bacteria) and as a consequence may aggregate with other bacteria. This can be advantageous in terms of survival however it may limit the areas in which they can live.
If a bacterium is larger than average with a low surface area: volume ratio it is likely REQUIRE SOME COMPESATING MECHANISM OR NUTRITIONAL ADVANTAGE to grow fast.
(??Although this may suggest that this impacts on their ability to cause disease several slow growing bacteria (such as M.tuberculosis) are sucessful pathogens. Consequently, it may suggest that bacteria with larger volumes require more adaptations to protect them whilst they grow (i.e. protect them from antibiotics in nature or from the immune system).??
PUNDIT:I WOULD SUGGEST THO, that extrapolations between size and disease are tenuous, though
I would also like to know to what extent the notion that larger = slow growing holds true.
PUNDIT: I would put it LARGER imposed a hurdle for fast growth that needs some physiological remedy.
Does that mean many soil bacteria which are slow growing are also large? Surely there are many other bacterial factors (such as enzymes to break down substrates) that influence growth other than size.
PUNDIT: I agree. I think though one can think cleary, if one identifis the limitation and limits in particular situtions imposed by small surface area, and their IMPLICATIONS. Also, appreciate that rod like or filamentous morphology, as opposed to spheres is an approach that increases surface area.
Similarly, what are examples of bacteria which undergo a dramatic change in size (with the exception of spore forming bacteria) during their life cycle or in response to different physiological conditions.
PUNDIT: There are some. Fast growing E. coli in rich medium is much bigger that slow growing E. coli. This is related to increase in ribosome content. Id have to think further to answer this better.
Microbe Pundit
To understand the point of my question you need to read about Eulopicium here for instance:
http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=1885516
The Epulos have a peripheral layer of highly convoluted membrane - increase in membrane area to compensate for surface are to volume challenge?
Microbe Pundit
Link gous here
J Bacteriol. 1991 September; 173(17): 5359–5362.
An unusual symbiont from the gut of surgeonfishes may be the largest known prokaryote.
K D Clements and S Bullivant
Pundit
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