AbstractsBiology & Animal Science

Nautela italica R11, a member of Roseobacter clade, has been described as a member of the epiphytic community of the temperate red alga Delisea pulchra. Under laboratory conditions, N. italica R11 causes a temperature induced bleaching disease in D. pulchra similar to what is observed in the field, yet little is understood regarding the mechanisms of virulence in this pathogen. Analysis of the N. italica R11 genome has identified a number of genes potentially involved in virulence including those encoding surface adhesion factors, oxidative stress resistance, proteolytic enzymes and toxins. Of particular interest are the genes encoding for repeats in toxin (RTX) proteins which are common to many bacterial pathogens and have a wide range of biological and biochemical activities. Moreover a recent proteomics study found that a set of predicted RTX proteins were overrepresented in N. italica R11 cells grown at disease inducing temperatures. Therefore the aims for this study were to begin to determine the biological function of the rtx genes by describing their expression under different conditions likely to be encountered by the pathogen N. italica R11 on the surface of D. pulchra. Quantitative real time PCR (qPCR) was performed on three putative RTX genes (RR11_486, RR11_392 and RR11_222) under different conditions (elevated temperature (25°C), presence of D. pulchra crude extracts and oxidative stress). For the purpose of this investigation, combinations of molecular and classical microbiological techniques were utilized. Differential expression was observed for the three RTX genes under the experimental conditions tested. The putative RTX proteins RR11_222 and RR11_486 present the same patterns of increased gene expression in presence of D. pulchra crude extract suggesting that these two proteins may have similar function. In contrast the putative RTX protein RR11_392 present an opposite pattern of expression being expressed at the higher temperature and decreased in the presence of D. pulchra crude extract. These expression patterns are supported by the sequence analysis, which also places these proteins into different functional groups in the RTX protein family. Furthermore the sequences analysis reveals N. italica R11 RTX proteins share the characteristics of known virulence factors. The observation that rtx gene expression increases in presence of D. pulchra chemical extract and at the disease inducing temperatures suggest a possible role for the three putative RTX proteins in the process of disease in D. pulchra.