N-Acyl homoserine lactone

N-Acyl homoserine lactones (Abbreviated as AHLs or N-AHLs) are a class of signaling molecules involved in bacterial quorum sensing, a means of communication between bacteria enabling behaviors based on population density.

The first AHL (N-3-(oxo-hexanoyl)-homoserine lactone) was found as the natural inducer of bioluminescence in the bacterium Vibrio fischeri.

In one study, AHL was shown to interact with eukaryotic cells, and mitigate an immune response and facilitates infection.

[3] AHLs are one of the major groups of the autoinducer (AI) molecules which are found primarily in gram-negative proteobacteria but also in some bacteriodetes, cyanobacteria, and archaea.

[4] The other two major groups are oligopeptides AIs in gram-positive bacteria; and autoinducer-2 (AI-2), as a universal signal for interspecies communications.

The LuxI gene is highly conserved, which indicates that although diverse, there are a limited number of AHL-type signals that are produced by bacteria.

However, in the AHL synthase enzyme family, the C-terminal region, which determines the type of substrates the synthetase can recognize and the subsequent acyl-chain length, is not conserved.

In the process of quorum sensing, first the LuxI protein synthesizes an acylated homoserin-lactone molecule which can pass through cell membrane along the gradient through diffusion to the environmental space.

[11] Moreover, the LuxR-AHL complex will upregulate the transcription of LuxI protein which will increase the production of AHLs (positive feedback loop).

Lactonases break down the lactone bonds in autoinducers, making them unable to bind to target transcriptional regulators and thereby increasing disease resistance.

Over the long history of coevolution of plants and microbes, plants have evolved to respond to the symbiotic or pathogenic microbes in appropriate ways with an adapted gene expression profile such as cooperation with bacterial saprotrophs leading to an endophytic life or defense responses against pathogens.

[17] Moreover, the water and mineral flow through the plant was higher as stomata opening increased, and therefore the overall transpiration rate changed.

The endophytic bacterium with AHL-autoinduction and produces a variety of long side-chain AHLs seems to assist the fungus to interact in a symbiotic manner with the colonized host plants.

When R. radiobacter F4 was inoculated to Arabidopsis or wheat (Triticum aestivum), it conferred similar stimulation of growth and yield, as well as priming of the defense responses and increasing environmental fitness.