Biofilm formation is inhibited by c-di-GMP in Acinetobacter baumannii

GOLIC A.E.; MARTÍNEZ F.; ZHOU J.; SINTIM H.; MUSSI M. A.

Córdoba

Congreso; 16th International Congress on Photobiology; 2014

GRAFOB- CONICET- Universidad Nacional de Córdoba

The ability of Acinetobacter baumannii to form biofilms could be central to its pathogenicity given that it contributes to its persistence and dissemination in the nosocomial setting, in addition to the bacterial resistance to antimicrobial compounds. We recently demonstrated that biofilm formation is modulated by light at 24ºC in this microorganism (Mussi et al., 2010), an aspect that could represent a key strategy in the control of the organism. Specifically, light results in inhibition of biofilm formation while it is highly stimulated in the dark. This bacterial response depends on the expression of the blue-light-sensing A (blsA) gene, which codes for a photoreceptor protein that contains an N-terminal blue-light-sensing-using flavin (BLUF) domain. In this work, we assayed different nucleotidic compounds on their ability to modulate biofilm formation, as some of them have been reported to modulate this trait in other organisms. Our results show that the addition of c-di-GMP inhibits biofilm formation in A. baumannii. Besides, when c-di-GMP was added to the ∆blsA mutant, which does not produce the photoreceptor and is therefore insensitive to light forming biofilms both under light or in the dark, biofilm formation was significantly attenuated under both conditions. Therefore, the addition of c-di-GMP resembles the illuminated condition, suggesting that, in analogy with other organisms, light could stimulate the production of this second messanger leading to the observed phenotype under illumination. To test the specificity of c-di-GMP as a biofilm blocker and to rule out the possibility that the effects on biofilms we observed were merely due to the presence of extracellular nucleotides in general or to that of cyclic mononucleotide (guanosine) analogs in particular, we performed similar experiments using GMP, cGMP and 8-Br-GMP (cGMP analog).Our results show that the effect was specific to c-di-GMP, as we did not find any effect with the other nucleotides. Briefly, A. baumannii can respond to the presence of extracellular c-di-GMP, resulting in the inhibition of biofilm formation. Whether this molecule is involved in the last steps of the light signal transduction is a possibility suggested by our results, but which yet needs further studies for confirmation.