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

Abstract

Light sensing in chemotrophic bacteria has been relatively recently ascertained. In the human pathogen Acinetobacter baumannii, light modulates motility, biofilm formation, and virulence through the blue-light-sensing-using flavin (BLUF) photoreceptor BlsA. In addition, light can induce a reduction in susceptibility to certain antibiotics, such as minocycline and tigecycline, in a photoreceptorindependent manner. In this work, we identified new traits whose expression levels are modulated by light in this pathogen, which comprise not only important determinants related to pathogenicity and antibiotic resistance but also metabolic pathways, which represents a novel concept for chemotrophic bacteria. Indeed, the phenylacetic acid catabolic pathway and trehalose biosynthesis were modulated by light, responses that completely depend on BlsA. We further show that tolerance to some antibiotics and modulation of antioxidant enzyme levels are also influenced by light, likely contributing to bacterial persistence in adverse environments. Also, we present evidence indicating that surfactant production is modulated by light. Finally, the expression of whole pathways and gene clusters, such as genes involved in lipid metabolism and genes encoding components of the type VI secretion system, as well as efflux pumps related to antibiotic resistance, was differentially induced by light. Overall, our results indicate that light modulates global features of the A. baumannii lifestyle.IMPORTANCE The discovery that nonphototrophic bacteria respond to light constituted a novel concept in microbiology. In this context, we demonstrated that light could modulate aspects related to bacterial virulence, persistence, and resistance to antibiotics in the human pathogen Acinetobacter baumannii. In this work, we present the novel finding that light directly regulates metabolism in this chemotrophic bacterium. Insights into the mechanism show the involvement of the photoreceptor BlsA. In addition, tolerance to antibiotics and catalase levels are also influenced by light, likely contributing to bacterial persistence in adverse environments, as is the expression of the type VI secretion system and efflux pumps. Overall, a profound influence of light on the lifestyle of A. baumannii is suggested to occur. KEYWORDS Acinetobacter baumannii, light, metabolismA cinetobacter baumannii is a threatening human pathogen considered to be the paradigm of multidrug resistance (MDR). A key component in its success as a pathogen is not only its outstanding capability to acquire resistance but also its peculiar

Trehalose, a temperature‐ and salt‐induced solute with implications in pathobiology of Acinetobacter baumannii

“…Up to 0.5 µmol trehalose/mg of protein were detected, but the differences may also be due to different extraction/detection procedures. Another interesting observation concerning trehalose biosynthesis in A. baumannii has been published very recently: expression of otsBA (and other genes) was shown to be modulated by light (Müller et al ., ). In A. baumannii ATCC 19606 wild type, 10 µmol trehalose/g dry weight (which equals ca.…”

Coping with low water activities and osmotic stress in Acinetobacter baumannii: significance, current status and perspectives

“…Whether the trehalose biosynthesis enzymes OtsA and OtsB are osmotically regulated as well, as in E. coli (Giæver et al ., ), remains to be established, but a transcriptional activation by the osmolarity of the environment was demonstrated (Zeidler et al ., ). Furthermore, high temperature as well as blue light stimulated transcription of otsBA and trehalose accumulation independent of high osmolarity (Müller et al ., ; Zeidler et al ., ). In contrast to the mtlD promoter, no suppression by other compatible solutes was found for the otsBA promoter, which can be explained by a role of trehalose in other stress responses and points towards a different mechanism of regulation (Zeidler et al ., ).…”

Human fluids alter DNA-acquisition in Acinetobacter baumannii

“…Recently, several in-vitro studies have shown that A. baumannii can respond to extracellular stimuli such as bile salts, mucin, light, antibiotics and human serum, among others, modifying the expression of genes involved in biofilm formation, degradation of phenylacetic acid, metabolic pathways, and genes coding for the Type VI secretion system (T6SS) [10,11]. In addition, in-vivo studies performed with a life-threatening bacteremia animal model using A. baumannii ATCC 17878-infected mice showed up-regulation of genes associated with three iron uptake systems, whereas genes related to metabolism, quorum sensing, and biofilm formation were down-regulated, highlighting the ability of A. baumannii to adapt to fluctuating environments [12].…”