Agriculture Reference
In-Depth Information
5. QS Mediated By Autoinducer 2 (AI-2)
AI-2 was originally identified as a QS autoinducer in
Vibrio harveyi
, which controls
bioluminescence in conjunction with an AHL-based mechanism [Henke and Bassler, 2004].
Interestingly, this regulation shares characteristics from QS-systems of both the Gram-
negative and Gram-positive bacteria, as it combines AHLs and a two-component protein
signal transduction system [Schauder and Bassler, 2001]. The gene responsible for ultimate
production of AI-2 is named
luxS
, and seems widely distributed as it was found present in
more than 60 bacterial species, including classes
β
,
γ
,
δ
and ε of the Proteobacteria,
Spirochaetes, Firmicutes, Actinobacteria, and other genera [Vendeville
et al.
, 2005], leading
to the suggestion that AI-2 can serve as one universal language [Sun
et al
., 2004].
Chemically, AI-2 is a collection of interconvertible furanone-derived molecules [Chen
et
al.
, 2002, Waters and Bassler, 2005, Chhabra
et al.
, 2005]. AI-2 emerges from DPD (4,5-
dihydroxy-2,3-pentanedione), which is a byproduct of the activated methyl cycle (AMC),
responsible for the generation of the methyl-donor
S
-adenosyl methionine (Figure 4)
[Williams
et al.
, 2007]. DPD was isolated and purified by Cao and Meighen (1989), who also
elucidated its structure. LuxS, a small metalloenzyme containing Fe
2+,
is an
S
-
ribosylhomocysteinase that cleavages
S
-ribosylhomocysteine to produce DPD [de
Keersmaecker
et al.
, 2006].
Figure 4. Pathways for detoxification of SAH and synthesis of DPD [Sun
et al.
, 2004].