Editing Digestion (section)

===Secretion systems===
{{Main|Secretion#Secretion in Gram negative bacteria}}

[[Bacteria]] use several systems to obtain nutrients from other organisms in the environments.

====Channel transport system====

In a channel transport system, several proteins form a contiguous channel traversing the inner and outer membranes of the bacteria. It is a simple system, which consists of only three protein subunits: the [[ATP-binding cassette family|ABC protein]], [[membrane fusion protein]] (MFP), and [[outer membrane protein]].{{Specify|date=May 2011}} This secretion system transports various chemical species, from ions, drugs, to proteins of various sizes (20–900 kDa). The chemical species secreted vary in size from the small ''Escherichia coli'' peptide colicin V, (10 kDa) to the ''Pseudomonas fluorescens'' cell adhesion protein LapA of 900 kDa.<ref name= Wooldridge>{{cite book |editor= Wooldridge K | year=2009 |title=Bacterial Secreted Proteins: Secretory Mechanisms and Role in Pathogenesis | publisher=Caister Academic Press | isbn= 978-1-904455-42-4}}</ref>

====Molecular syringe====

A [[type III secretion system]] means that a molecular syringe is used through which a bacterium (e.g. certain types of ''Salmonella'', ''Shigella'', ''Yersinia'') can inject nutrients into protist cells. One such mechanism was first discovered in ''Y. pestis'' and showed that toxins could be injected directly from the bacterial cytoplasm into the cytoplasm of its host's cells rather than be secreted into the extracellular medium.<ref name=Salyers>Salyers, A.A. & Whitt, D.D. (2002). ''Bacterial Pathogenesis: A Molecular Approach'', 2nd ed., Washington, DC: ASM Press. {{ISBN|1-55581-171-X}}</ref>

====Conjugation machinery====
The [[Bacterial conjugation|conjugation]] machinery of some bacteria (and archaeal flagella) is capable of transporting both DNA and proteins. It was discovered in ''Agrobacterium tumefaciens'', which uses this system to introduce the Ti plasmid and proteins into the host, which develops the crown gall (tumor).<ref name=Cascales>{{cite journal |vauthors=Cascales E, Christie PJ |title=The versatile Type IV secretion systems |journal=Nature Reviews Microbiology |volume=1 |issue=2 |pages=137–149 |year=2003 |doi=10.1038/nrmicro753 |pmid=15035043|pmc=3873781 }}</ref> The VirB complex of ''Agrobacterium tumefaciens'' is the prototypic system.<ref name=Christie>{{cite journal |author1=Christie PJ |author2=Atmakuri K |author3=Jabubowski S |author4=Krishnamoorthy V |author5=Cascales E. |title=Biogenesis, architecture, and function of bacterial Type IV secretion systems |journal=Annu Rev Microbiol |volume=59 |pages=451–485 |year=2005 |issue=1 |doi=10.1146/annurev.micro.58.030603.123630 |pmid=16153176|pmc=3872966 }}</ref>

In the [[Diazotroph|nitrogen-fixing]] ''[[Rhizobia]]'', conjugative elements naturally engage in inter-[[Kingdom (biology)|kingdom]] conjugation. Such elements as the ''[[Agrobacterium]]'' Ti or Ri plasmids contain elements that can transfer to plant cells. Transferred genes enter the plant cell nucleus and effectively transform the plant cells into factories for the production of [[opines]], which the bacteria use as carbon and energy sources. Infected plant cells form [[Agrobacterium tumefaciens|crown gall]] or [[Agrobacterium rhizogenes|root tumors]]. The Ti and Ri plasmids are thus [[endosymbiont]]s of the bacteria, which are in turn endosymbionts (or parasites) of the infected plant.

The Ti and Ri plasmids are themselves conjugative. Ti and Ri transfer between bacteria uses an independent system (the ''tra'', or transfer, operon) from that for inter-kingdom transfer (the ''vir'', or [[virulence]], operon). Such transfer creates virulent strains from previously avirulent ''Agrobacteria''.

====Release of outer membrane vesicles====
In addition to the use of the multiprotein complexes listed above, [[gram-negative bacteria]] possess another method for release of material: the formation of [[outer membrane vesicle]]s.<ref name=Chatterjee>{{Cite journal
 | pmid = 4168882|doi=10.1099/00221287-49-1-1
| year = 1967
| last1 = Chatterjee
| first1 = S.N.
| title = Electron microscopic observations on the excretion of cell-wall material by ''Vibrio cholerae''
| journal = Journal of General Microbiology
| volume = 49
| issue = 1
| pages = 1–11
| last2 = Das
| first2 = J
| doi-access = free
}}</ref><ref>{{Cite journal
 | pmid = 16291643
| year = 2005
| last1 = Kuehn
| first1 = M.J.
| title = Bacterial outer membrane vesicles and the host-pathogen interaction
| journal = Genes & Development
| volume = 19
| issue = 22
| pages = 2645–2655
| last2 = Kesty
| first2 = N.C.
| doi = 10.1101/gad.1299905
| doi-access = free
}}</ref>  Portions of the outer membrane pinch off, forming spherical structures made of a lipid bilayer enclosing periplasmic materials.  Vesicles from a number of bacterial species have been found to contain virulence factors, some have immunomodulatory effects, and some can directly adhere to and intoxicate host cells.  While release of vesicles has been demonstrated as a general response to stress conditions, the process of loading cargo proteins seems to be selective.<ref name=McBrrom>{{Cite journal
| last1 = McBroom | first1 = A.J.
| last2 = Kuehn | first2 = M.J.
| doi = 10.1111/j.1365-2958.2006.05522.x
| title = Release of outer membrane vesicles by Gram-negative bacteria is a novel envelope stress response
| journal = Molecular Microbiology
| volume = 63
| issue = 2
| pages = 545–558
| year = 2007
| pmid = 17163978
| pmc =1868505
}}</ref>

[[Image:Venus Flytrap showing trigger hairs.jpg|thumb|right|125px|Venus Flytrap (''Dionaea muscipula'') leaf]]