CEFOBI   05405
CENTRO DE ESTUDIOS FOTOSINTETICOS Y BIOQUIMICOS
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Staring at the cold sun: blue light regulation of motility and biofilm formation is widely distributed within the genus Acinetobacter
Autor/es:
ADRIÁN GOLIC; MARIO VANEECHOUTTE; ALEJANDRO VIALE; LUIS ACTIS; MARÍA A. MUSSI
Lugar:
Mar del Plata
Reunión:
Congreso; VIII Congreso de Microbiología General; 2012
Resumen:
We previously demonstrated that the Gram-negative opportunistic human pathogen Acinetobacter baumannii senses and responds to blue light. At 24°C, cells form spreading colonies in the dark, but remained at the inoculation point when incubated under blue light. Blue light also inhibited the formation of biofilms and pellicles in broth grown cultures. These bacterial responses depend on the expression of the blue-light-sensing A (blsA) gene, which codes for a protein that contains an N-terminal blue-light-sensing-using flavin (BLUF) domain and lacks a detectable effector domain. Interestingly, temperature plays a role in the ability of A. baumannii to sense and respond to light, as the photoregulation is not observed at 37ºC. One of the most intriguing questions arising from our previous study is related to whether other non-baumannii members of the Acinetobacter genus also show the ability to sense blue light. To address this question, we screened databases for the presence of BLUF-domain containing proteins in the available sequenced genomes of members of this genus. Using the retrieved sequences (and also including sequences from other bacteria and lower eukarya), we inferred their phylogenetic relationships from amino acidic alignments constructed using only the BLUF domain. These analyses showed that all of the Acinetobacter putative photoreceptors were grouped together in a monophyletic cluster, indicating that they share a common origin and no horizontal gene transfer events have occurred with members of other bacteria or eukarya. We analyzed next whether the non-baumannii Acinetobacter species were actually able to move and respond to light at 24 °C. From all the strains studied, A. calcoaceticus, A. nosocomialis, A. pitii, A. baylyi, A. bouvettii and A. tjernbergiae showed light-dependent regulation of motility. We further evaluated whether biofilm formation was also photoregulated in the other species within the genus at 24°C, and found that many species did, such as A. calcoaceticus, A. nosocomialis, A. guillouiae, A. ursingii, A. venetianus, A. pitii, A. beijerinckii, A. lwoffii, A. towneri, A. gerneri, A. johnsonii, A. baylyi, A. bereziniae. The environmental species A. baylyi harbors four genes encoding putative BLUF photoreceptors. We assayed next whether any of these proteins were able to complement the A. baumannii blsA mutant at 24°C, which has lost photoregulation due to the mutation. Three A. baylyi photoreceptors were able to fully complement the blsA gene in motility assays, while only partially did ACIAD2110. Regarding photoregulation of biofilm formation, all photoreceptors restored the original phenotype. Overall, we show that light regulation is not restricted to A. baumannii but, rather, is widespread within the Acinetobacter genus. In particular, other members of the A. baumannii-calcoaceticus complex (a subgroup that contains the clinical most relevant species) share with A. baumannii the ability to sense light at 24°C reflected both by motility and biofilm formation assays. Finally, the four A. baylyi photoreceptors were able to complement the A. baumannii blsA mutant, therefore showing the redundancy in function existent between photoreceptors of different species such as baumannii and baylyi.