general bacterial anatomy

[jarisky]

Hello everyone. I'm new to scienceforums.net and I have some questions about the anatomy of bacteria. I've arrived at these questions because I'm a 3D computer graphics artist working for a company that makes educational software in the fields of medical anatomy, biology, and other areas of science. There are a lot of tidbits I'm wondering about, but I'm going to start with just a few questions so as not to overwhelm the good folks here.

 

Chromsomes: Do all bacteria have closed-circle, single-helix chromosomes? I've seen a few sources saying this but haven't found a lot about it, and have seen some diagrams showing a sort of spiral strand-shaped chromosome whose ends do not connect to each other. Also, I read that Brucella Abortus has two circular chromosomes; are there any other bacteria with more than one chromosome?

 

Plasmids: Are there certain genera and/or species that usually contain naturally-occurring plasmids, or does it vary per specimen? Is there only one instance of any given plasmid in a specimen, or several? Is there a general rule to determine which bacteria with naturally-occurring plasmids have single-stranded plasmids, and which have double-stranded plasmids?

 

Thanks much for whatever insight you all are able to provide! If there are recommended resources that address these questions (or a different forum I may have missed), I'm all ears.

 

P.S. For those of you who are curious, the company I work for is Cyber-Anatomy at http://www.cyber-anatomy.com/ and my own art portfolio is at http://www.jariensky.com

[CharonY]

Just to nitpick, anatomy generally refers to higher organisation of multicellular organisms. The more often used term in this context would be cellular organization.

 

To your questions

 

Chromsomes: Do all bacteria have closed-circle, single-helix chromosomes? I've seen a few sources saying this but haven't found a lot about it, and have seen some diagrams showing a sort of spiral strand-shaped chromosome whose ends do not connect to each other. Also, I read that Brucella Abortus has two circular chromosomes; are there any other bacteria with more than one chromosome?

 

 

Not all bacterial genomes are organized that way. That being said, the vast majority of known bacteria have a single chromosome, that can be coiled differently depending on activity (chromsomes can show quite a degree of organizational structures). But in most cases they are circular. Some bacteria (such as e.g. rhizobia) have several chromsomes. Some really are classified as megaplasmids, though. The distinction between really big plasmids and chromosomes can be a bit blurry and is often made according to whether they are essential. In addition, some bacteria (e.g. Agrobacterium) also have also linear chromsomes (usually in addition to circular ones, but there are exceptions like Borrelia).

 

Plasmids: Are there certain genera and/or species that usually contain naturally-occurring plasmids, or does it vary per specimen? Is there only one instance of any given plasmid in a specimen, or several? Is there a general rule to determine which bacteria with naturally-occurring plasmids have single-stranded plasmids, and which have double-stranded plasmids?

 

Thanks much for whatever insight you all are able to provide! If there are recommended resources that address these questions (or a different forum I may have missed), I'm all ears.

 

P.S. For those of you who are curious, the company I work for is Cyber-Anatomy at http://www.cyber-anatomy.com/ and my own art portfolio is at http://www.jariensky.com

 

 

Many bacterial species are almost always found with plasmids. In the end, it can be species, or even strain-specific. AFAIK all rhizobia possess plasmids on which their ability to induce root nodules are coded, for instance. The copy number of a given plasmid in single cell can vary a lot. Megaplasmids are often present in one copy, whereas high copy plasmids can go over 1000 copies (though it is very rare in naturally occuring plasmids). Plasmids, are normally double-stranded. They form singl-stranded intermediates during replication, for instance.

 

 

As source I would recommend any good microbial genetics or microbial cell biology text book. They usually have very good illustriations that you may be interested in.

[jarisky]

Thank you very much for the explanation, CharonY, that's very helpful!

[Guest meercy]

Any bacterial cell whether it is a coccus or a bacillus will have some structures common. These structures are cell

wall, cell membrane, cytoplasm, ribosomes and the chromosome. Other intro-cellular structures such as plasmid,

inclusion bodies and extra-cellular structures such as capsule, imbrication and flagella are possessed only by some

bacteria.

Glycol/Capsule/Slime:

A gelatinous polysaccharides or polypeptide outer covering of certain bacteria is called glycol x. These are the

structures that surround the outside of the cell envelope. The glycol is referred to as a capsule if it is firmly

attached to the cell wall, or as a slime layer if loosely attached.To know more about go to Bacterial.

Edited October 18, 2011 by meercy

[CharonY]

Actually there is quite a variety for basically all the components described. Gram+ and Gram- cell walls are vastly different, for instance, but even among the groups there are larges structural differences. The one that is probably most conserved is the ribosome complex, the rest has all kind of variations (including number of chromosomes, linear vs circular and so on). I have never heard the term glycol x in this context. What you refer to is most likely exopolysaccharides. As the name implies it is not a polyether.