Yes, they have.
Don’t you believe it?
A) Synechococcus carboxysome
B) The same but negatively stained and closer
C) H. neapolitanus carboxysome
D) Negative stain of H. neapolitanus carboxysome, you can even see RuBisCO assemblies inside
E) S. enterica Typhimurium LT2 enterosomes
F and G) Negatively stained enterosomes from S. enterica Typhimurium LT2
From Cannon et al, 2001
To date two different types “organelles” have been found in bacteria: carboxysomes and enterosomes. The first ones present in cyanobacteria and chemoautotrophic bacteria, the latter ones in some enterobacteria such as E. coli and S. enterica.
By definition they are polyhedral inclusion bodies that are bound by a unilamellar protein… so they are coated! it’s not only an agregation of enzymes or some substance produced by the bacteria, say, magnetite in Magnetospirillum, for example.
Carboxisomes are filled with 1,5-biphosphate carboxylase/oxygenase (RuBisCO) and the function could be to prevent the enzyme from being inhibited by oxygen. Anyhow, the catalytic properties of the enzyme are significantly enhanced inside this carboxysomes.
Enterosomes contain enzymes involved in the degradation of ethanolamine or propendiol. Some bacteria, like S. enterica, are found to have both types of enterosomes (they are independent) Havemann et al, 2003. A recent study done by Sriramulu et al (personal communication) introduced in E. coli the genes needed to produce the enzymes and the proteins of the coat for propendiol enterosomes. E. coli naturally only has the genes to produce enterosomes for ethanolamine degradation. And, Voila! they got nice and round enterosomes when they cultured the mutant on propendiol as an only source of carbon.
Personally, I’m not much convinced whether to call this an organelle or not, at least semantically they seem to be. The thing is that they are only temporary, so when the source starts being added they produce them and after the supply finishes they disappear. So, to put it bluntly, we have enzymatic pots in here!
All of this came because I was wondering, how come that bacteria don’t have organelles, in fact, after reading about this I still have a similar question, How come that bacteria don’t have biphospholipidic-layer organelles? It only takes a bit of invaginated membrane to get some sort of “lysosome”.
If anybody has found the missing link in the organelle issue, please let me know.
Anyway if not, place your bets…
Try “Planctomycetes”. These are a deep-branching line of (eu)bacteria displaying unusual features: lack peptidoglycan and have membrane-bound internal compartments. The nucleoid is compartmentalized in the so-called pirellulosome surrounded by a single membrane. In one species the nucleoid is even surrounded by a nuclear envelope consisting of two membranes, which joint at irregular gaps (so they are continous!) in a manner much alike eukaryotes. These data may support the endogenous karyogenic hipothesis on nuclear origins. It will be fascinating to further studying these creatures, as they may give us clues about eukaryotic origins. One Planctomycete species shows a proteome 8% similar to the eukaryotes.
Comment by Enrique — February 18, 2006 @ 1:16 pm
Very interesting, Thanks Enrique!!
Comment by Administrator — March 20, 2006 @ 3:48 pm