1
$\begingroup$

Among the 6 secretion systems in bacteria, can these 6 ways be sorted out in the order of how harmful it is to the human host? Like say type 3 is highly virulent so that comes first, but I don't know about the rest of the systems. Being a computer science student, I have failed to understand the Wikipedia article to derive this order. Does a discrete order even exist? Can anyone answer this question?

$\endgroup$
1
$\begingroup$

Theoretically there are two very basic things to consider in judging virulence for the secretion systems: a) Can it secrete into any human cell? (If not, chances of being virulent are smaller, but not zero as whatever is secreted in the environment of a cell could also be harmful for the cell.) b) Does it secrete some agent (protein, RNA, molecule), which is potentially harmful for a human cell?

a) alone is not sufficient for it to be virulent if b) is not also given. (As it could inject something in a cell that the cell can handle without a problem.) b) alone is not sufficient, as it has to get inside the cell somehow. Although, b) alone can work, if the agent has another way to get inside a cell or to harm the cell from outside.

So, generally, without knowing ALL the bacterial secretion systems and secreted agents, it is impossible to decide if one secretion system (alone) is always, sometimes or never harmful.

$\endgroup$
  • $\begingroup$ So these 6 categories does not include all the secretion types? $\endgroup$ – girl101 Jul 22 '15 at 12:22
  • $\begingroup$ All we know, I would say. But that was not what I meant to point out. The mere existence of a secretion system does not mean there is something harmful to be secreted, or that it can be secreted into a human cell. Even if the "generalised system" is said to be able to secrete into a human cell, there might be mutations in some bacteria which change it into being less or more effective. Even if the secretion system is not mutated, the bacteria might need additional systems to adhere to a cell or adhere more strongly. $\endgroup$ – skymningen Jul 22 '15 at 13:15
  • $\begingroup$ I think I did not quite get this answer. I think the questio is much easier than you say. In general the majority of the secretion systems are know to be used by symbiotic and pathogenic bacteria to interact with other bacteria and eukaryotes. Now, there is a huge amount of literature on the T3SS. It is used by pathogenic bacteria to alter immune response and cytoskeleton of the host and allow the delivering cells to colonize the host cells without being digested. $\endgroup$ – efrem Jul 22 '15 at 15:16
  • $\begingroup$ So if you refer to pathogens, well then you can consider the T3SS as an archetype of virulence factor. Instead, T4SS, T5SS and T6SS can also have other function besides virulence. So in general is the bacteria you are dealing with is described to be a pathogen, and has a T3SS, 99% this T3SS will be involve in virulence. $\endgroup$ – efrem Jul 22 '15 at 15:18
  • $\begingroup$ The presence alone of the SS does not allow you to define if a bacterium is pathogenic or not, but knowing the lifestyle of the bacterium you can be quite sure that if these systems are present, they are used for virulence. Just keep in mind that T1,2,4,5,6 can have additional function than virulence. $\endgroup$ – efrem Jul 22 '15 at 15:18
1
$\begingroup$

I think you cannot find a better answer then the following review:

http://www.nature.com/nrmicro/journal/v13/n6/full/nrmicro3456.html

It was published in 2015, and it gives a good overview about the secretion systems. Anyway, T6SS can also be virulent. Vibrio cholerae can use an effector of this SS to cross-link actin in the host cell and modify its morphology and its cytoskeleton behaviour. In general I think that there is not a general order of virulence, also because the T3SS was discovered long ago. Whereas, the T6SS just recently, so the amount of information about its function is still somehow limited.

Hope this helps.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.