BIODIVERSITAS ISSN: 1412-033X Volume 23, Number 8, August 2022 E-ISSN: 2085-4722 Pages: 4336-4342 DOI: 10.13057/biodiv/d230859 Screening of quorum quenching activity of rhizobacteria against Pectobacterium carotovorum subsp. carotovorum SAFIRA RIZKA LESTARI 1,♥ , FERY ABDUL CHOLIQ 2 , ANTOK WAHYU SEKTIONO 2 , MOCHAMMAD SYAMSUL HADI 2 , HAIDAR FARI ADITYA 1 , NONI RAHMADHINI 1 , RAMADHANI MAHENDRA KUSUMA 1 , YOGO SETIAWAN 2 1 Faculty of Agriculture, Universitas Pembangunan Nasional Veteran Jawa Timur. Jl. Rungkut Madya No. 1, Surabaya 60294, East Java, Indonesia.  email: safira.rizka.agro@upnjatim.ac.id 2 Department Plant Pests and Diseases, Faculty of Agriculture, Universitas Brawijaya. Jl. Veteran, Malang 65145, East Java, Indonesia Manuscript received: 3 April 2022. Revision accepted: 8 August 2022. Abstract. Lestari SR, Choliq FA, Sektiono AW, Hadi MS, Aditya HF, Rahmadhini N, Kusuma RM, Setiawam Y. 2022. Screening of quorum quenching activity of rhizobacteria against Pectobacterium carotovorum subsp. carotovorum. Biodiversitas 23: 4336-4342. Quorum sensing (QS) is a mechanism for determining the virulence of the phytopathogenic bacterium Pectobacterium carotovorum. P. carotovorum carries out the QS mechanism with the chemical compound acyl-homoserine lactone (AHL) to signal and carry out its pathogenicity and virulence. The pathogenicity of P. carotovorum can be prevented through quorum quencher (QQ) activity derived from bacteria that degrade AHL compounds by producing AHL-lactonase. In the present investigation, AHL-lactonase-producing bacteria were isolated from the rhizosphere of carrot cultivation in Bumiaji Sub-District, City of Batu, East Java, Indonesia. The isolated bacteria were screened for quorum quenching activity. Out of thirty-seven isolates, 7 rhizospheric bacteria showed QQ activity against the Chromobacterium violaceum bioindicator. The hypersensitivity test on tobacco plants showed that, five strains SRL07, SRL09, SRL15, SRL21, and SRL35 did not cause a hypersensitivity response. The five isolates were able to suppress the virulence of P. carotovorum in carrot tubers. The 16S rRNA gene sequences of the five isolates had the highest similarity to Bacillus thuringiensis, B. subtilis, and B. cereus. The five isolates were detected to have the gene encoding AHL-lactonase (aiiA). The present study provides new information about the QQ activity of rhizosphere and its potential as a quorum quencher against P. carotovorum. Keywords: AHL-lactonase, biocontrol, Pectobacterium carotovorum, quorum quenching INTRODUCTION Quorum sensing (QS) is a bacterial mechanism for sharing information among cells that depends on the density of bacterial colonies (Rutherford and Bassler 2012). The function of QS is to convey signals in the form of chemical compounds to bacterial colonies (Zhao et al. 2020; Pangastuti et al. 2021). Chemical compounds that act as signals in QS, in general, include (1) acyl-homoserine lactones (AHLs), (2) auto-inducing peptides (AIPs), and (3) auto-inducer 2 (AI-2) (Huang et al. 2016). Gram- negative plant pathogenic bacteria carry out the QS mechanism with the chemical compound acyl-homoserine lactone (AHL) as a signal to carry out their pathogenicity and virulence (LaSarre and Federle 2013). Pectobacterium carotovorum subsp. carotovorum is a Gram-negative and common soil-borne bacterium that causes soft rot disease of various plant hosts, such as vegetables and fruits (Abd-El-Khair et al. 2021). P. carotovorum is the cause of soft rot disease in carrots, potatoes, lettuce, onions, and cabbage (Lee et al. 2016; Fan et al. 2017). Pectobacterium carotovorum employs 3-oxo- hexanoyl homoserine lactone (3OC6HSL) to regulate the expression of genes encoding virulence factors such as pectate lyases, proteases, and cellulase enzymes (Garge and Nerurkar 2016). In Indonesia, P. carotovorum also attacks carrot plants. One of the obstacles in carrot cultivation is the soft rot disease caused by the phytopathogenic bacteria P. carotovorum (Marquez-villavicencio et al. 2011; Máisuría and Nerurkar 2013). Soft rot disease causes potatoes to be watery, mushy, and blackish, making them unsuitable for sale. Currently, management efforts to control soft rot disease that have been carried out involve applying synthetic bactericides, performing minimum tillage, eradicating, and irradiating with LED lights. Another strategy that can be implemented is to control the pathogenicity of P. carotovorum by utilizing the quorum quenching (QQ) mechanism (Fan et al. 2020; Zhang et al. 2020). The QQ mechanism is a QS prevention or inhibition mechanism. The QQ mechanism can be carried out in three ways: degradation and inactivation of QS signal molecules, inhibition of the biosynthesis of QS signal molecules, and inhibition of detection of QS signal molecules (Natrah et al. 2011). QQ inactivates AHL in expressing genes encoding virulence factors in phytopathogens (Baltenneck et al. 2021). Romero et al. (2008) and Utari et al. (2017) reported that specific plant cells and certain bacterial cells could inhibit QS by producing compounds with structures similar to AHL but act as the inhibitors and produce AHL-degrading enzymes, namely AHL-lactose. The QQ mechanism is considered safer for controlling phytopathogens without usage of bactericides because it does not cause resistance to phytopathogens (Rehman and Leiknes 2018).