Study of the surface structures from Xanthomonas citri subsp. citri

PETROCELLI S; BELTRAMINO M; ARANA MR; MOYANO LAURA; MOREIRA LM; ORELLANO EG

Rosario

Congreso; IX Congreso Argentino de Microbiología General; 2013

The adhesion of pathogenic bacteria to the surface of the host cell is an important step in the colonization of plant. Pathogenic bacteria have molecules or structures capable of interacting with different types of surfaces. These molecules are called adhesins, and include filamentous appendages, called pili. The type IV pili (Tfp) is among the most widely distributed and best studied structure. In addition to their role in eukaryotic cell adhesion, the Tfp is essential for other bacterial functions, including natural transformation, autoaggregation, biofilm and fruiting bodies formation. The Tfp is also responsible of the flagellar independent translocation known as twitching motility. Moreover, in plant pathogenic bacteria, the Tfp is involved in host colonization and in the pathogenesis process, including the activation of defense responses in the host cell. Xanthomonas citri subsp. citri (Xac) is the phytopathogen responsible for citrus canker type A, one of the most devastating diseases of citrus crops worldwide. In Xac there are three potential genes encoding the structural subunit of the pili called fimA, fimA1 and pilA. In a previous work we have begun to study the pilA gene. We have constructed a mutant strain in this gene and characterized the bacterial physiology of wild type and mutant bacteria. We observed different patterns of in vitro adhesion to the polystyrene plates and in vivo adhesion to the surface of orange leaves, in the bacterial motility and in the biofilm formation. In the present work we have characterized the biofilm development using a Xanthomonas strain expressing GFP and also we studied the role of the pili during the bacterial interaction with the host plant. Moreover, we have made an in silico study of the proteins encoded by genes fimA, fimA1 and pilA. The sequences of these proteins and homologous proteins of other pathogenic bacteria were compared performing alignments of amino acid sequences. We constructed a phylogenetic tree that allowed us to observe that PilA and FimA proteins belong to two distinct groups. We performed an analysis of the secondary structures and a prediction of the tertiary structures and in both cases the proteins showed conserved structural elements and similar spatial distribution. In order to predict potential interaction targets of the pilin we built a network of genes pilA, fimA and fimA1 observing interaction with genes related with xanthan production and another gene involved in the pilus polymerization.