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Classification of Microbes

About microscopic forms of life, including Bacteria, Archea, protozoans, algae and fungi. Topics relating to viruses, viroids and prions also belong here.

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Classification of Microbes

Postby bionewbie » Mon Dec 12, 2005 6:38 am

Why is it so difficult to classify microes? For example Cyanobacteria were originally classified with algae, as streptomyces are grouped with fungi.
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Postby Poison » Mon Dec 12, 2005 7:08 am

Well, actually classifying some microorganisms is difficult. For example, some organisms carry both animal and plant characteristics. So where to classify them? It is about the characteristics they have, they are not exactly plant or exactly animal.
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Postby Ken Ramos » Mon Dec 12, 2005 10:57 am

Poison is right, it can be very confusing at times as to what is actually what. At one time I was studying Plasmodial Slime Molds (Moulds). They are grouped by some as a fungi (Myxomycetes) and as animals by others (Mycetozoa). This is because they begin their existance as a flagellated amoeba, sometimes refered to a myxo-amoeba, which fuse together with other like ameba, to form a plasmodium. This plasmodium which is now a multinucleate amoeba can be seen with the naked eye and can be as large as several inches, will soon change over to a sometimes brightly colored fungi, producing fruiting bodies. There is still much debate as to where to place these organisms. Mostly they are refered to at present, as Myxomycetes. :)

If you wish to observe this wonder of nature, myxomycetes can be found growing in the summer time on the forest floor in damp places among the fallen leaves and on decaying wood and other decaying organic matter. A good 10X hand lens is recommended for field study and a stereomicroscope for lab work.

Many protozoa also share this plant and animal trait, namely the Phylum Mastigophora, the flagellates. Euglena, Phacus and Peranema are good examples. Of course a good transmitted light microscope is needed to observe these organisms. :)
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Postby bionewbie » Mon Dec 12, 2005 1:00 pm

So, would microbes be classified based on their origins then? Would the same parameters be sued to classify fungi with those that are used to classify bacteria?
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Postby Ken Ramos » Tue Dec 13, 2005 12:24 am

Well, I don't know about bacteria or fungi but I will stick my neck out and say the taxon is probably based on the morphology and/or physiology of the organism. :)
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Postby canalon » Tue Dec 13, 2005 2:55 am

Bacterial taxonomy needs a particular kind of mind. The kind that enjoy splitting hairs in thousands of pieces just because you can ;)
In fact the difficulty comes that if it is rather straightforward to define species when you have stable characters and species (even only grossly), it become harder when there is no rule that do not have exceptions (Escherichia coli are supposed to be Beta-glucuronidase positive, but O157:H7 is not, and Salmonella enterica are mostly lactose negative but not all subspecies, and there are some exceptions in the other subspecies anyway). If you add to the mix the fact that they tend to exchange DNA over species, genus, that you can see differences in genome size of more than 20% in the same species, that naming rely on tradition and should be kept so for clinical reason (Shigella spp. are in fact a subgroup of E. coli which have a particular plasmid, Yersinia pestis should in fact be a Pasteurella if I don't mix things up).

So wide distinctions are easy: Gram+/Gram-, Bacilli/Cocci. But even the definition of a species is not easy.
So either you are a hair splitter and you go into the field of bacterial taxonomics, or you don't and you do what you can with your samples, knowing that in a way there will always be samples taht will be impossible to classify.
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Postby Inuyasha » Tue Dec 13, 2005 11:16 pm

Simple and Clean as the kingdom of hearts soundtrack would say. It is because species are defined mainly through the biological method. AKA. Species can reproduce with only their own kind and not with other species due to postzygotic and prezygotic mechanisms. Because microbes are mostly asexual, this definition can not be used. And more ummm. "uncertain ones" are plugged in.
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