m. r. alimanesh

Quorum sensing (QS) is a process of cell to cell communication that allows bacteria to be aware about cell density. In this phenomenon bacteria communicate with each other through signaling molecules such as N-acylhomoserine lactones (AHLs). Also, virulence gene expression in many pathogenic bacteria like Pectobacterium is under control of QS. Some bacteria can degrade AHLs molecules by a process called anti quorum sensing or quorum quenching (QQ); therefore, QQ can be used in biocontrol of plant pathogenic bacteria. The main purpose of this research was to detect QQ genes in strong QQ-based biocontrol bacteria.

In this investigation, QQ bacteria were isolated from rhizosphere and phyllosphere of some agricultural and non-agricultural plants using minimum media containing AHL. QQ bacteria were identified using biosensors CV026 and VIR07. Mechanism of QQ action was determined by heating, proteinase treatment and filtering methods. Afterwards, in order to find acylase and lactonase genes in these bacteria, homology searches were performed using BLASTn and BLASTp in NCBI. Then, several primers were designed by several softwares including CLC main workbench 5.5, Primer Premier 6, Primer3, Oligo7 and primer BLAST.

The most abundant and strongest QQ isolates were shown enzymatic activity. Main twenty-seven isolates with high QQ activity were detected. Four genera and species including Pseudomonas chlororaphis, Pseudomonas putida, Acinetobacter sp. and Bacillus sp. were found as the bacteria with highest QQ and biocontrol ability against Pectobacterium. As a results of this study, in the Bacillus Aiia lactonase gene;in P. chlororaphis three acylase genes of pvdQ، quiP and hacB; in P.putida two acylase genes of  pvdQ and quiP  and in Acinetobacter one acylase genes were traced.

According to the results of this investigation, Pseudomonas genus was determined as the frequent QQ bacteria. Also, P. chlororaphis species with the strongest QQ activity, were divided in to two groups; the first isolates with two acylase genes (pvdQ and quiP) and the second isolates containing extra homologous acylase hacB. Isolates of the latter group with the most detected genes involved in QQ, were identified as the best QQ-based biocontrol bacteria against Pectobacterium.