Browsing by Author "Gomelsky, Mark"

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    DhhP, a Cyclic di-AMP Phosphodiesterase of Borrelia burgdorferi, Is Essential for Cell Growth and Virulence
    (ASM, 2014-05) Ye, Meiping; Zhang, Jun-Jie; Fang, Xin; Lawlis, Gavin B.; Troxell, Bryan; Zhou, Yan; Gomelsky, Mark; Lou, Yongliang; Yang, X. Frank; Department of Microbiology and Immunology, IU School of Medicine
    Cyclic di-AMP (c-di-AMP) is a recently discovered second messenger in bacteria. Most of work on c-di-AMP signaling has been done in Gram-positive bacteria, firmicutes, and actinobacteria, where c-di-AMP signaling pathways affect potassium transport, cell wall structure, and antibiotic resistance. Little is known about c-di-AMP signaling in other bacteria. Borrelia burgdorferi, the causative agent of Lyme disease, is a spirochete that has a Gram-negative dual membrane. In this study, we demonstrated that B. burgdorferi BB0619, a DHH-DHHA1 domain protein (herein designated DhhP), functions as c-di-AMP phosphodiesterase. Recombinant DhhP hydrolyzed c-di-AMP to pApA in a Mn2+- or Mg2+-dependent manner. In contrast to c-di-AMP phosphodiesterases reported thus far, DhhP appears to be essential for B. burgdorferi growth both in vitro and in the mammalian host. Inactivation of the chromosomal dhhP gene could be achieved only in the presence of a plasmid-encoded inducible dhhP gene. The conditional dhhP mutant had a dramatic increase in intracellular c-di-AMP level in comparison to the isogenic wild-type strain. Unlike what has been observed in Gram-positive bacteria, elevated cellular c-di-AMP in B. burgdorferi did not result in an increased resistance to β-lactamase antibiotics, suggesting that c-di-AMP's functions in spirochetes differ from those in Gram-positive bacteria. In addition, the dhhP mutant was defective in induction of the σS factor, RpoS, and the RpoS-dependent outer membrane virulence factor OspC, which uncovers an important role of c-di-AMP in B. burgdorferi virulence.
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    Positive and Negative Regulation of Glycerol Utilization by the c-di-GMP Binding Protein PlzA in Borrelia burgdorferi
    (American Society for Microbiology, 2018-10-23) Zhang, Jun-Jie; Chen, Tong; Yang, Youyun; Du, Jimei; Li, Hongxia; Troxell, Bryan; He, Ming; Carrasco, Sebastian E.; Gomelsky, Mark; Yang, X. Frank; Microbiology and Immunology, School of Medicine
    Borrelia burgdorferi, the causative agent of Lyme disease, encounters two disparate host environments during its enzootic life cycle, Ixodes ticks and mammalian hosts. B. burgdorferi has a small genome that encodes a streamlined cyclic dimeric GMP (c-di-GMP) signaling system comprising a single diguanylate cyclase, Rrp1, and two phosphodiesterases. This system is essential for spirochete survival in ticks, in part because it controls the expression of the glp operon involved in glycerol utilization. In this study, we showed that a B. burgdorferi c-di-GMP receptor, PlzA, functions as both a positive and a negative regulator for glp expression. Deletion of plzA or mutation in plzA that impaired c-di-GMP binding abolished glp expression. On the other hand, overexpression of plzA resulted in glp repression, which could be rescued by simultaneous overexpression of rrp1. plzA overexpression in the rrp1 mutant, which is devoid of c-di-GMP, or overexpression of a plzA mutant incapable of c-di-GMP binding further enhanced glp repression. Combined results suggest that c-di-GMP-bound PlzA functions as a positive regulator, whereas ligand-free PlzA acts as a negative regulator for glp expression. Thus, PlzA of B. burgdorferi with a streamlined c-di-GMP signaling system not only controls multiple targets, as previously envisioned, but has also evolved different modes of action.IMPORTANCE The Lyme disease pathogen, Borrelia burgdorferi, has a simple cyclic dimeric GMP (c-di-GMP) signaling system essential for adaptation of the pathogen to the complicated tick environment. The c-di-GMP effector of B. burgdorferi, PlzA, has been shown to regulate multiple cellular processes, including motility, osmolality sensing, and nutrient utilization. The findings of this study demonstrate that PlzA not only controls multiple targets but also has different functional modalities, allowing it to act as both positive and negative regulator of the glp operon expression. This work highlights how bacteria with a small genome can compensate for the limited regulatory repertoire by increasing the complexity of targets and modes of action in their regulatory proteins.