Expressed genes of Xylella fastidiosa at slow and fast growing conditions

Abstract

Plant associated bacteria produce extra-cellular polysaccharides (EPS) that may be correlated to pathogenicity, and play important role in the survival capacity of bacteria, increasing the adhesion capacity within the hosts (plant and vectors) and to other bacterial cells. The need to modulate EPS synthesis in a variety of niches may help to explain the multiplicity of genetic regulatory mechanisms that has become evident, particularly in the plant pathogens. Ultra-structural studies of Xylella fastidiosa strains in xylem vessel have shown a cell aggregates immersed in electron dense region, probably composed by extra-cellular polysaccharide. The aggregate colonies appeared to help together and to help to attach to vessel cell walls by extra-cellular strands produced by the bacteria. Primary isolation of X. fastidiosa of the plant takes long time to develop small solid and compact colonies. If they will not transfer to another media, primary isolates grows as mucoid colonies with formation of a ring around it, and concomitantly growth of new adherent micro-colonies .We call this characteristic as colony morphology at slow growing conditions. On the other hand, after subcultures of the primary colony occurs a lost of the characteristic above described. This lost is directly proportional to the number of sub-cultures, and is more severe in liquid medium under, agitation and aeration. We call this characteristic as colony morphology at fast growing conditions. If we assume that the pathogenicity of Xylella fastidiosa in sweet orange could be correlated to the blocking of xylem vessels causing water stress, and that blocking results of aggregate formation of colonies by synthesis of EPS within the xylem, slow growth conditions in vitro after bacteria isolation could be similar to those conditions in planta. The differential expression of genes in both conditions would open a real possibility to find out genes associated to pathogenicity. The goals of this proposal are to evaluate and compare the differential expression of genes at slow and fast growing conditions, by pathogenicity tests in seedlings of sweet orange and periwinkle, differential display of mRNA, Northern analysis and, according to the number of expressed sequences, by micro-array. The proposal goes from experimental observations to genome information. (AU)