Identification of Quorum-Quenching <i>N</i> -Acyl Homoserine Lactonases from <i>Bacillus</i> Species

TLDR

Gram‑negative bacteria use N‑acyl homoserine lactone (AHL) molecules as quorum‑sensing signals to regulate functions such as virulence, and AHL is also known as an autoinducer. The study aims to identify more than 20 bacterial isolates capable of enzymatically inactivating AHLs. The authors cloned the aiiA AHL‑lactonase gene from Bacillus sp. strain 240B1, screened over 20 isolates for activity, selected eight with strong activity for taxonomic analysis, and cloned nine AHL‑inactivation genes from the selected isolates by functional cloning or PCR.

Abstract

ABSTRACT A range of gram-negative bacterial species use N -acyl homoserine lactone (AHL) molecules as quorum-sensing signals to regulate different biological functions, including production of virulence factors. AHL is also known as an autoinducer. An autoinducer inactivation gene, aiiA , coding for an AHL lactonase, was cloned from a bacterial isolate, Bacillus sp. strain 240B1. Here we report identification of more than 20 bacterial isolates capable of enzymatic inactivation of AHLs from different sources. Eight isolates showing strong AHL-inactivating enzyme activity were selected for a preliminary taxonomic analysis. Morphological phenotypes and 16S ribosomal DNA sequence analysis indicated that these isolates probably belong to the species Bacillus thuringiensis. Enzymatic analysis with known Bacillus strains confirmed that all of the strains of B. thuringiensis and the closely related species B. cereus and B. mycoides tested produced AHL-inactivating enzymes but B. fusiformis and B. sphaericus strains did not. Nine genes coding for AHL inactivation were cloned either by functional cloning or by a PCR procedure from selected bacterial isolates and strains. Sequence comparison of the gene products and motif analysis showed that the gene products belong to the same family of AHL lactonases.