Temperature stress promotes cell division arrest in Xanthomonas citri subsp citri

Citrus canker is an economically important disease that affects orange production in some of the most important producing areas around the world. It represents a great threat to the Brazilian and North American citriculture, particularly to the states of SAo Paulo and Florida, which together correspond to the biggest orange juice producers in the world. The etiological agent of this disease is the Gram-negative bacterium Xanthomonas citri subsp. citri (Xcc), which grows optimally in laboratory cultures at similar to 30 degrees C. To investigate how temperatures differing from 30 degrees C influence the development of Xcc, we subjected the bacterium to thermal stresses, and afterward scored its recovery capability. In addition, we analyzed cell morphology and some markers of essential cellular processes that could indicate the extent of the heat-induced damage. We found that the exposure of Xcc to 37 degrees C for a period of 6h led to a cell cycle arrest at the division stage. Thermal stress might have also interfered with the DNA replication and/or the chromosome segregation apparatuses, since cells displayed an increased number of sister origins side-by-side within rods. Additionally, Xcc treated at 37 degrees C was still able to induce citrus canker symptoms, showing that thermal stress did not affect the ability of Xcc to colonize the host citrus. At 40-42 degrees C, Xcc lost viability and became unable to induce disease symptoms in citrus. Our results provide evidence about essential cellular mechanisms perturbed by temperature, and can be potentially explored as a new method for Xanthomonas citri synchronization in cell cycle studies, as well as for the sanitation of plant material. (AU)