Assessing of auto-inducer type-1 (AI-1) molecule N-(3-hydroxybutanoyl)-L-homoserine lactone responsible for quorum sensing mechanisms in marine pathogenic bacterium Vibrio harveyi.

In shrimp farming systems, Vibrio harveyi is recognized as one of the foremost pathogens. This bacterium possesses multiple virulence factors that contribute to its pathogenic behavior. Like many Gram-negative bacteria, V. harveyi regulates gene expression through quorum sensing (QS), a cell-density-dependent communication process. During QS, signal molecules known as N-acyl-homoserine lactones (AHLs) are produced, enabling bacteria to coordinate physiological traits. These diffusible signal molecules are also called auto-inducers (AIs), as they accumulate in the environment and trigger coordinated gene expression once a threshold concentration is reached. In recent studies, a strain of V. harveyi was isolated and confirmed through biochemical assays and further validated using PCR. Its quorum sensing ability was evaluated using a bioassay with the biosensor strain Chromobacterium violaceum (CV026). When V. harveyi was streaked alongside C. violaceum CV026, the biosensor strain produced a purple pigment, indicating the presence of AHL molecules and confirming QS activity. In contrast, a non-AHL producing strain such as Bacillus mycoides did not induce pigmentation in C. violaceum CV026. AHLs were then extracted from V. harveyi and analyzed using LC-MS. The results confirmed the presence of an AHL molecule. Based on LC-MS analysis and the C. violaceum CV026 bioassay, the pathogenic V. harveyi strain was found to produce the AI-1 signal molecule N-(3-hydroxybutanoyl)-L-homoserine lactone (C4-HSL), which is known to play a key role in quorum sensing in V. harveyi.