CONICET | Buscador de Institutos y Recursos Humanos

Pseudomonas syringae pv. tomato DC3000 causes bacterial speck of tomato, a widely spread disease that causes significant economic losses worldwide, that is representative of numerous bacterial plant diseases for which effective controls are still needed [1]. It is known that chitosan (Ch) has biocide action against a broad bacterial spectrum. However, its action on phytopathogenic bacteria has been poorly explored. In this work, we report that chitosan application on P. syringae suspension cells causes biochemical and cellular changes resulting in cell aggregation and impaired growth. Chitosan (MW: 70,000 and DD: 78 %) used in this work was obtained from prawn and shrimp exoskeletons by a chemical procedure. P. syringae suspension cultures showed a dosedependent response to Ch application on the optical density (OD). Cell cultures treated for 24 h with Ch concentrations ≥ 50 μg/ml showed a significant decrease in the OD (Figure 1). To evaluate how Ch works, cells from exponential growth phase were incubated for 24 h at 30 °C with shaking in fresh medium supplemented or not (control) with 100 μg/ml Ch. A remarkable aggregation was observed only in P. syringae cells exposed to Ch treatment (Figure 2). In order to analyze plasma membrane damage in treated cells we used the fluorogenic dye SYTOX Green [2]. This molecular probe only penetrates cells that have damaged plasma membranes and fluoresces upon binding to DNA. Figure 2 shows that the fluorescent probe was incorporated into aggregated P. syringae cells. However, the fluorescence was not detected in non-treated cells indicating a Ch-mediated membrane permeabilization effect. In summary, the observed sensitivity of P. syringae cells to Ch application in the in vitro experiments prompts us to further evaluate its application as a biopesticide in plant crops.