Blue light directly modulates the quorum network in the human pathogen Acinetobacter baumannii

Abstract

Quorum sensing modulates bacterial collective behaviors including biofilm formation, motility and virulence in the important human pathogen Acinetobacter baumannii. Disruption of quorum sensing has emerged as a promising strategy with important therapeutic potential. In this work, we show that light modulates the production of acyl-homoserine lactones (AHLs), which were produced in higher levels in the dark than under blue light at environmental temperatures, a response that depends on the AHL synthase, AbaI, and on the photoreceptor BlsA. BlsA interacts with the transcriptional regulator AbaR in the dark at environmental temperatures, inducing abaI expression. Under blue light, BlsA does not interact with AbaR, but induces expression of the lactonase aidA and quorum quenching, consistently with lack of motility at this condition. At temperatures found in warm-blooded hosts, the production of AHLs, quorum quenching as well as abaI and aidA expression were also modulated by light, though in this case higher levels of AHLs were detected under blue light than in the dark, in a BlsA-independent manner. Finally, AbaI reduces A. baumannii's ability to kill C. albicans only in the dark both at environmental as well as at temperatures found in warm-blooded hosts. The overall data indicate that light directly modulates quorum network in A. baumannii.

BfmRS encodes a regulatory system involved in light signal transduction in the human pathogen Acinetobacter baumannii.

“…Particularly, we have accumulated a large amount of evidence about the light signal transduction and physiological responses at moderate temperatures such as 23°C, which are mainly but not only governed by the blue light using FAD (BLUF)-type photoreceptor BlsA 1,3−10 . We have also shown that A. baumannii responds to light at 37°C modulating virulence in an epithelial infection model using human keratinocytes in culture 7 , as well as quorum sensing 10 , through a BlsA-independent mechanism 7,10 . However, the light signal perception and transduction components operating at this temperature were not yet identi ed.…”

“…Blue light treatments. Blue light treatments were performed as described in our previous studies [1][2][3][4][6][7][8][9][10]32 . Brie y, cells were incubated for 24 hours (or else as speci ed) at 37°C in the dark or under blue light emitted by 9-light-emitting diode (LED) arrays, with an intensity of 6 to 10 µmol photons/m 2 /s.…”

“…From analyses of ours as well as other researchers' data 18 , we observed that the BfmRS system and light integrate signals into the same pathways in A. baumannii. In fact, BfmR/S and light regulate catalase production 4,25 ; the phenylacetic acid degradation pathway 3,18 ; the acetoin catabolic pathway; trehalose biosynthesis; pellicle formation 3,12 , and bio lm formation 3,13 ; as well as expression of the Acinetobactin operon 8 , the adeA, adeB and adeC components 6,18 , genes coding for the e ux pump emrAB 4,18 , components of the quorum sensing machinery such as abaI 10,18 , mbria 4,18 and the T6SS system 12 .…”

BfmRS encodes a regulatory system involved in light signal transduction modulating motility and desiccation tolerance in the human pathogen Acinetobacter baumannii

“…Particularly, we have accumulated a large amount of evidence about the light signal transduction and physiological responses at moderate temperatures such as 23 °C, which are mainly but not only governed by the blue light using FAD (BLUF)-type photoreceptor BlsA 1 – 11 . We have also shown that A. baumannii responds to light at 37 °C modulating virulence in an epithelial infection model using human keratinocytes in culture 11 , as well as quorum sensing 10 , through a BlsA-independent mechanism 10 , 11 . However, the light signal perception and transduction components operating at this temperature were not yet identified.…”

“…From analyses of ours as well as other researchers’ data 20 , we observed that the BfmRS system and light integrate signals into the same pathways in A. baumannii. In fact, BfmR/S and light regulate catalase production 3 , 23 ; the phenylacetic acid degradation pathway 4 , 20 ; the acetoin catabolic pathway 9 ; trehalose biosynthesis; pellicle formation 4 , 16 , and biofilm formation 4 , 14 ; as well as expression of the Acinetobactin operon 8 , genes coding for the AdeABC efflux pump 7 , 20 , genes coding for the efflux pump EmrAB 3 , 20 , components of the quorum sensing machinery such as abaI 10 , 20 , fimbria 3 , 20 and the T6SS system 16 . Furthermore, it has been shown that BfmR interacts with BlsA mostly in the dark 29 .…”