RESEARCH LETTER E¡ects of the antimicrobial peptide gomesin on the global gene expression pro¢le, virulence and bio¢lm formation of Xylella fastidiosa Andr ´ ea C. Fogac ¸a 1 , Paulo A. Zaini 1 , Nelson A. Wulff 2 , Patr´ ıcia I.P. da Silva 1 , Marcos A. F ´ azio 3 , Anto ˆ nio Miranda 3 , Sirlei Daffre 4 & Aline M. da Silva 1 1 Departamento de Bioqu´ ımica, Instituto de Qu´ ımica, Universidade de Sa ˜ o Paulo, Sa ˜o Paulo, SP, Brazil; 2 Fundo de Defesa da Citricultura, Araraquara, SP, Brazil; 3 Departamento de Biof´ ısica, Universidade Federal de Sa ˜ o Paulo, Sa ˜o Paulo, SP, Brazil; and 4 Departamento de Parasitologia, Instituto de Cie ˆ ncias Biom ´ edicas, Universidade de Sa ˜ o Paulo, Sa ˜o Paulo, SP, Brazil Correspondence: Aline M. da Silva, Departamento de Bioqu´ ımica, Instituto de Qu´ ımica, Universidade de Sa ˜ o Paulo, Sa ˜o Paulo, SP 05508-000, Brazil. Tel.: 155 11 3091 2182; fax: 155 11 3091 2186; e-mail: almsilva@iq.usp.br Present address: Andr ´ ea C. Fogac ¸a, Departamento de Parasitologia, Instituto de Cie ˆ ncias Biom ´ edicas, Universidade de Sa ˜o Paulo, Sa ˜ o Paulo, SP 05508-000, Brazil. Received 19 October 2009; revised 27 January 2010; accepted 28 February 2010. Final version published online 30 March 2010. DOI:10.1111/j.1574-6968.2010.01950.x Editor: Mark Schembri Keywords antimicrobial; phytopathogen; microarray; gene expression profile. Abstract In the xylem vessels of susceptible hosts, such as citrus trees, Xylella fastidiosa forms biofilm-like colonies that can block water transport, which appears to correlate to disease symptoms. Besides aiding host colonization, bacterial biofilms play an important role in resistance against antimicrobial agents, for instance antimicrobial peptides (AMPs). Here, we show that gomesin, a potent AMP from a tarantula spider, modulates X. fastidiosa gene expression profile upon 60 min of treatment with a sublethal concentration. DNA microarray hybridizations revealed that among the upregulated coding sequences, some are related to biofilm production. In addition, we show that the biofilm formed by gomesin-treated bacteria is thicker than that formed by nontreated cells or cells exposed to streptomycin. We have also observed that the treatment of X. fastidiosa with a sublethal concentration of gomesin before inoculation in tobacco plants correlates with a reduction in foliar symptoms, an effect possibly due to the trapping of bacterial cells to fewer xylem vessels, given the enhancement in biofilm production. These results warrant further investigation of how X. fastidiosa would respond to the AMPs produced by citrus endophytes and by the insect vector, leading to a better understanding of the mechanism of action of these molecules on bacterial virulence. Introduction Xylella fastidiosa is a xylem-restricted Gram-negative gam- maproteobacterium that colonizes several economically im- portant crops causing severe diseases, such as the citrus variegated chlorosis (Chang et al., 1993). Infected suscepti- ble hosts exhibit water-stress symptoms that have been associated with the formation of a bacterial biofilm inside the xylem vessels, resulting in blockage of the water trans- port (Chatterjee et al., 2008). It is well known that besides aiding host colonization, biofilms significantly increase bacterial resistance to antimicrobial compounds (Mah & O’Toole, 2001). Xylella fastidiosa can be graft transmitted to healthy plants or vectored by several species of xylem- feeding leafhoppers (Redak et al., 2004). Antimicrobial peptides (AMPs) are defensive substances widespread in nature, being produced from bacteria to mammals (Sang & Blecha, 2008). The majority display common features such as a low molecular mass, a positive net charge at physiological pH and an amphipathic structure (Bulet et al., 2004). Generally, AMPs disrupt the plasmatic membrane, causing the rapid death of microorganisms. Nevertheless, some AMPs can cross the microbial mem- brane acting on internal cellular targets (Brogden, 2005). The elucidation of the exact mode of action of AMPs is essential to allow the use of these substances to develop a new generation of antibiotics to control infections of both plants and animals. Gomesin is a short b-hairpin AMP (2270.4 Da) isolated from the hemocytes of the tarantula spider Acanthoscurria gomesiana (Silva et al., 2000). Similar FEMS Microbiol Lett 306 (2010) 152–159 c  2010 Federation of European Microbiological Societies Published by Blackwell Publishing Ltd. All rights reserved MICROBIOLOGY LETTERS Downloaded from https://academic.oup.com/femsle/article/306/2/152/561833 by guest on 30 June 2022