Tolerância de Aeromonas spp. ao estresse salino

Abstract

The bacteria from the Aeromonas genus are important aquatic microorganisms and causative agents of infectious diseases in animals, and even to mankind. Its wide distribution in continental aquatic and marine environments is an indicative of its ability to adapt to different levels of salinity, which is a relevant fact concerning food contamination. The bacterial tolerance to saline stress is associated with the maintenance of cellular homeostasis through ion transportation systems and the accumulation of organic solutes, such as betaine, proline, among others. Betaine is an osmoprotectant found in plants, animals and microorganisms, transported in bacteria by a transportation system of the ABC specific type, encoded by operon ProU. In this context, the objectives of this study were: to measure the tolerance to saline stress in Aeromonas, including determining the growth and cell viability in Aeromonas in saline stress, evaluate the expression of betaine transport genes after saline stress and create an in silico analysis of the proU operon in Gram negative bacteria. The results demonstrate that Aeromonas trota present more salinity tolerance than Aeromonas hydrophila, and that some Aeromonas species can grow in minimal environment containing up to 0.42 M of NaCl, concentration used as a food preservative agent. The betaine acts as an osmoprotectant in Aeromonas, determining their capacity to survive and grow in higher concentrations of sodium chloride (0.51 to 0.68 M). On the other hand, the choline, considered as an important betaine precursor in some bacteria, presents no osmoprotectant effect on Aeromonas. The evaluation of pre-growth with betaine show that this osmoprotectant is accumulated even in the absence of stress, determining a bacterial pre-adaptation to changes in osmolarity. The in silico analysis of the operon proU, responsible for betaine transportation, shows their high conservation in bacteria, indicating the importance of this ABC transporter. Expression experiments of the operon proU in A. hdydrophila showed constitutive basal expression and significant increase of the operon proU expression in bacteria exposed to osmotic stress, even in the absence of the osmoprotectant. Therefore, the operon proU expression in A. hydrophila is modulated by intracellular stress, in such manner, that it returns to close baseline levels when the cell reaches homeostasis.