Research Paper Identification and analysis of the salt tolerant property of AHL lactonase (AiiA TSAWB ) of Bacillus species Nalini Easwaran, Sivashanmugam Karthikeyan, Balasundaram Sridharan and Kodiveri Muthukaliannan Gothandam School of Biosciences and Technology, VIT University, Vellore, India Bacterial biofilms communicate by a process called Quorum Sensing. Gram negative bacterial pathogens specifically talk through the production, detection, and response to the signal or autoinducer called Acyl Homoserine Lactones. Bacterial lactonases are important AHL hydrolysing or quorum quenching enzymes. The present study deals with ten endospore forming gram positive isolates of the saltern soil. Preliminary screening for Quorum Quenching activity with the QS Inhibition indicator strain Chromobacterium violaceum ATCC 12472, showed positive activity in four isolates namely TS2, TS16, TSAWB, and TS53B. AHL lactonase (AiiA) specific primers amplified Acyl Homoserine Lactone lactonase gene in the TSAWB genome alone. Phylogenetic relationship of the identified AiiA TSAWB confirmed its evolutionary relationship with bacterial AiiA like AHL lactonase of the metallo-beta-lactamase super family. Our in vitro AHL hydrolysis assay under wide percentage (0–5) of salt solutions with TSAWB isolate and also its intracellular soluble protein fraction showed halotolerant AHL hydrolysis ability of the AiiA TSAWB enzyme. In silico determination of putative tertiary structure, the ESBRI derived conserved salt bridges, aminoacid residue characterization with high mole percent of acidic and hydrophobic residues reaffirmed the halotolerant ability of the enzyme. So we propound the future use of purified AiiA TSAWB , as hypertonic suspension for inhalation to substitute the action of inactivated host’s paraoxonase in treating Pseudomonas aeruginosa infection in cystic fibrosis patients. Abbreviations: QS – quorum sensing; QQ – quorum quenching; AHL – acyl homoserine lactone; AHL lactonase – acyl homoserine lactone lactonase; CF – cystic fibrosis Keywords: Quorum sensing / Quorum quenching / Acyl homoserine lactone signal molecules / Acyl homoserine lactone lactonase / Salt Bridges Received: January 7, 2014; accepted: June 10, 2014 DOI 10.1002/jobm.201400013 Introduction Biofilms are group of microbes that are adhered in an interface of solid and liquid, on living or nonliving surfaces and are typically surrounded by an extracellular matrix (polysaccharides, proteins, lipids, eDNA) substan- ces [1]. Biofilm mode of growth is induced by stresses like temperature, pH, salinity, antibiotics, host immune response, protozoan grazing etc., Biofilm facilitates nutrient acquisition and provides stable structured environment for genetic exchange like conjugation and transformation which are the basics for evolution of new traits [2]. Biofilms are beneficial in industries like wastewater treatment, biomining, and bioremediation plants. Biofilms are harmful in chronic inflammations or infections and are responsible for 60% of all antibiotic resistant infections. In industry, bacterial biofilms lead to many problems like fouling of ship hulls, corrosion in pipes and contamination of food processing equipments. Quorum Sensing plays an important role in microbial biofilm formation. QS is a bacterial communication process that depends on the production, detection and response to signaling molecules or auto inducers [3]. QS allows bacterial population to change their behaviour in response to differences in population density and species composition Correspondence: K. M. Gothandam, School of Biosciences and Technology, VIT University, Vellore-632014, India E-mail: gothandam@yahoo.com Phone: 914162202616 Fax: 914162243029 Environment  Health  Techniques Identification of AHL lactonase isolate from saltern 579 ß 2014 WILEY-VCH Verlag GmbH & Co. KGaA,Weinheim www.jbm-journal.com J. Basic Microbiol. 2015, 55, 579–590