EXPLORING UV-B RESPONSES AND BIOFILM FORMATION IN THE CYANOBACTERIUM Synechococcus PCC 7335.

DELUCA, I; FERNÁNDEZ, MB; CORREA ARAGUNDE, N

Congreso; XVIII Congreso de la Sociedad Argentina de Microbiología General; 2023

Nitric oxide (NO) is a signal molecule that is involved in a great variety of physiological responses in different organisms. To produce NO, the enzyme nitric oxide synthase (NOS) uses L-arginine as a substrate. In photosynthetic organisms, an increase in NO levels is detected upon UV-B irradiation, which triggers defense responses. One of the mechanisms that microorganisms use to protect themselves in unfavorable situations is the production of an extracellular matrix that resists the stress condition as an adhesive multicellular state known as biofilm. The composition of these secreted extracellular polymeric substances (EPS) is mainly polysaccharides, which provide the necessary structure to the biofilm. NO and arginine have been related to biofilm formation or cell dispersion in different bacterial strains. Exposure to UV-B radiation has been reported to affect biofilm formation or modify the chemical and physical composition of the extracellular matrix in order to provide protection to microorganisms. However, in cyanobacteria, this response was not deeply explored. The aim of this work was to investigate: i) the impact of UV-B exposure on biofilm formation; and ii) the participation of the NOS enzyme and the production of EPS during this response in the cyanobacterium Synechococcus PCC 7335. Our results show that both UV-B irradiation and arginine supplementation increased NO production in S. PCC 7335. Arginine induces biofilm formation in a dose-dependent manner up to 1 mM, while 5 mM arginine and exposure to UV-B inhibit it. The addition of the NOS inhibitor (L-NAME) and the NO scavenger cPTIO abolished biofilm formation, suggesting the involvement of the NOS enzyme in this process. The drop in biofilm formation was not attributed to cell death in stress conditions since cell viability was confirmed using the fluorescent probe Sytox Green. Furthermore, exopolysaccharides could play a major role in this response since an increase in these was observed when the cyanobacteria were exposed to increasing intensities of UV-B. Thus, it can be concluded that UV-B stress induces the production of NO and triggers the dispersal of the biofilm in Synechococcus PCC 7335. Moreover, the exopolysaccharides secreted during the UV-B response might be part of an early protection strategy but seem not to be related to biofilm production in this strain.