More Than Just Light: Clinical Relevance of Light Perception in the Nosocomial Pathogen Acinetobacter baumannii and Other Members of the Genus Acinetobacter

Abstract

A summary of the major findings concerning light modulation in Acinetobacter baumannii, which governs aspects related to the success of this microorganism as a nosocomial pathogen, is presented. Particularly, the evidence shows that light modulates the ability of the bacteria to persist in the environment, its virulence against eukaryotic hosts and even susceptibility to certain antibiotics. The light signal is sensed through different mechanisms, in some cases involving specialized photoreceptors of the BLUF-type, whereas in others, directly by a photosensitizer molecule. We also provide new data concerning the genomic context of BLUF-domain containing proteins within the genus Acinetobacter, as well as further insights into the mechanism of light-mediated reduction in susceptibility to antibiotics. The overall information points toward light being a crucial stimulus in the lifestyle of members of the genus Acinetobacter as well as in other clinically relevant species, such as members of the ESKAPE group, playing therefore an important role in the clinical settings. INTRODUCTIONOur planet is one of the few places in universe close enough to one star that its whole surface bathes in light, and where life can take place. Each human cell and most forms of life on Earth synchronize their activities taking into account this ubiquitous environmental signal.In addition to incident solar radiation, humans and other organisms are exposed to artificial and man-made electromagnetic radiation used for indoor and outdoor lighting, medical diagnosis and treatment of diseases (1).However, the effects light produces on living organisms are far from being completely understood. In the case of bacteria, extensive knowledge has been accumulated for phototrophs, which capture light to convert it into chemical bond energy or electrochemical potential for processes dedicated to satisfy cellular energy requirements (2,3). However, information recalled during the last decades indicates that this signal also plays a role in the physiology of environmental and pathogenic chemotrophic nonphototrophic prokaryotes (3-5). Pertinent examples include physiological responses as diverse and interesting as morphogenesis in Stigmatella aurantiaca (6); carotenogenesis in Streptomyces coelicolor (7) and Myxococcus xanthus (8,9); the general response to stress in Bacillus subtilis (10,11); the attachment of Caulobacter crescentus to glass surfaces (12); the photophobic response and various biofilm functions in Escherichia coli (13,14); biofilm formation in Idiomarina loihiensis (15); motility in Acinetobacter calcoaceticus and other Acinetobacter species (16)(17)(18)(19)(20). Light signals perceived by nonphotosynthetic bacteria may even modulate their interactions with hosts (5,21). For instance, light regulates the general stress response and infection of macrophages by Brucella abortus (22,23), the virulence of Agrobacterium tumefaciens toward cucumber (24); the invasiveness of Listeria monocytogenes for enterocytes (25); the nodulation o...

Colistin Resistant A. baumannii: Genomic and Transcriptomic Traits Acquired Under Colistin Therapy

“…These bacterial responses depended on the expression of the Ab ATCC 17978 A1S_2225 gene named blue-light-sensing A ( blsA ). The light modulated motility and biofilm formation (Ramírez et al, 2015a), more precisely motility and formation of biofilms and pellicles, were observed only when bacterial cells were incubated in darkness. Furthermore, the same authors demonstrated that susceptibility to minocycline and tigecycline, two antibiotics used for the treatment of MDR A. baumannii infections, was modulated by light (Ramírez et al, 2015b).…”

BlsA integrates light and temperature signals into iron metabolism through Fur in the human pathogen Acinetobacter baumannii

“…Retrotranscription and qRT-PCR analysis were done as described in reference 39 , using primers listed in Table S2 in the supplemental information. Data are presented as NRQ (Normalized relative quantities) calculated by the qBASE method 40 , using recA and rpoB genes as normalizers 6 .…”

Light Modulates Metabolic Pathways and Other Novel Physiological Traits in the Human Pathogen Acinetobacter baumannii

“…7A). The participation of BOF proteins in biofilm formation, motility, and virulence in response to quorum-sensing and hormonal signals (10) has been reported in some organisms. Moreover, a cluster of genes coding for a de-Nacetylase of the phosphatidylinositol-glycan biosynthesis class L protein (PIG-L) superfamily (DJ41_1943), followed by a methyltransferase gene (DJ41_1944) and a glycosyltransferase gene (DJ41_1955, which changes only 0.5-fold with respect to dark conditions), also located in the vicinity of blsA, are upregulated under blue light.…”

“…Finally, we have presented evidence indicating that light modulates susceptibility to minocycline and tigecycline antibiotics in Acinetobacter, as well as other clinically relevant pathogens, by a BlsA-independent mechanism that most likely involves induction of the expression of resistance genes by singlet oxygen (8,10).…”