Leptospirosis, caused by spirochetes of the genus Leptospira, is a globally widespread, neglected and emerging zoonotic disease. While whole genome analysis of individual pathogenic, intermediately pathogenic and saprophytic Leptospira species has been reported, comprehensive cross-species genomic comparison of all known species of infectious and non-infectious Leptospira, with the goal of identifying genes related to pathogenesis and mammalian host adaptation, remains a key gap in the field. Infectious Leptospira, comprised of pathogenic and intermediately pathogenic Leptospira, evolutionarily diverged from non-infectious, saprophytic Leptospira, as demonstrated by the following computational biology analyses: 1) the definitive taxonomy and evolutionary relatedness among all known Leptospira species; 2) genomically-predicted metabolic reconstructions that indicate novel adaptation of infectious Leptospira to mammals, including sialic acid biosynthesis, pathogen-specific porphyrin metabolism and the first-time demonstration of cobalamin (B12) autotrophy as a bacterial virulence factor; 3) CRISPR/Cas systems demonstrated only to be present in pathogenic Leptospira, suggesting a potential mechanism for this clade’s refractoriness to gene targeting; 4) finding Leptospira pathogen-specific specialized protein secretion systems; 5) novel virulence-related genes/gene families such as the Virulence Modifying (VM) (PF07598 paralogs) proteins and pathogen-specific adhesins; 6) discovery of novel, pathogen-specific protein modification and secretion mechanisms including unique lipoprotein signal peptide motifs, Sec-independent twin arginine protein secretion motifs, and the absence of certain canonical signal recognition particle proteins from all Leptospira; and 7) and demonstration of infectious Leptospira-specific signal-responsive gene expression, motility and chemotaxis systems. By identifying large scale changes in infectious (pathogenic and intermediately pathogenic) vs. non-infectious Leptospira, this work provides new insights into the evolution of a genus of bacterial pathogens. This work will be a comprehensive roadmap for understanding leptospirosis pathogenesis. More generally, it provides new insights into mechanisms by which bacterial pathogens adapt to mammalian hosts.

Lyme disease was reproduced in specific pathogen-free beagle dogs by exposure to Borrelia burgdorferi-infected ticks (Ixodes dammini). Seroconversion and disease frequency were higher after exposure to infected adult ticks than to infected nymphs. Young pups developed clinical disease more readily than older dogs. The incubation period lasted 2-5 months. Acute recurrent lameness with fibrinopurulent arthritis was the dominant clinical sign. Dogs recovered but developed persistent mild polyarthritis. B. burgdorferi persisted in recovered dogs for at least 1 year. Isolation of B. burgdorferi and detection by polymerase chain reaction was most successful from skin biopsies at the site of the tick bite. Antibody to B. burgdorferi antigens was first detected by ELISA and Western blots by 4-6 weeks after exposure. High serum levels persisted during 17 months of observation. In contrast to infection from ticks, inoculation of dogs with cultured B. burgdorferi resulted in seroconversion with a shorter duration of antibody persistence and no clinical disease.

No abstract

Pathogenic Leptospira spp. express immunoglobulin-like proteins, LigA and LigB, which serve as adhesins to bind to extracellular matrices and mediate their attachment on host cells. However, nothing is known about the mechanism by which these proteins are involved in pathogenesis. We demonstrate that LigBCen2 binds Ca 2؉ , as evidenced by inductively coupled plasma optical emission spectrometry, energy dispersive spectrometry, 45 binding plays a pivotal role in the pathogenesis of leptospirosis.Leptospira spp. are spirochetes, including the pathogenic species Leptospira interrogans as well as the saprophytic species Leptospira biflexa. Leptospirosis, a zoonotic disease caused by Leptospira spp., is widely distributed in developing countries and has reemerged in the United States (1). The severe form of leptospirosis, Weil's syndrome, includes an acute febrile illness associated with multiorgan damage, such as liver failure (jaundice), renal failure (nephritis), pulmonary hemorrhage, and meningitis (2), with a mortality rate up to 15% if not treated (3). Several virulence factors of this organism have been identified, including the sphingomyelinases, serine proteases, zincdependent proteases, collagenase (4), LipL32 (5), lipopolysaccharide (6), a novel factor H, laminin-and fibronectin-binding protein (Lsa24 or Len) (7-9), Loa22 (10), and Lig (leptospira immunoglobulin-like) proteins (11-13).Lig proteins, which include LigA and LigB, possess bacterial immunoglobulin-like (BIg) 3 domains with 90-amino acid tandem repeats. Both proteins have identical N-terminal sequences of 630 amino acids, but their C termini are variable (11-13). LigB also encodes a C-terminal, nonrepeat domain with 771 amino acid residues (11, 12). LigA and LigB may serve as microbial surface components recognizing adhesive matrix molecules that allow pathogenic Leptospira to bind to host extracellular matrix components, such as fibronectin (Fn), fibrinogen, laminin, and collagen (14 -16). Lig proteins may also serve as possible vaccine candidates and/or as diagnostic antigens (12,17,18), and their expression is regulated by osmolarity (19). A high affinity Fn binding region of LigB, designated LigBCen2, contains 152 amino acids that include part of an immunoglobulin-like domain and a nonrepeated region (15) (Fig. 1A).Calcium plays a pivotal role in bacterial physiological activities, such as cell cycle, cell division (20), competence (21), pathogenesis (22), signal transduction (23), and motility and chemotaxis (24,25). Apart from these functions, it is also known that host-pathogen interactions of some bacteria are affected by calcium (26,27). Several types of Ca 3 The abbreviations used are: BIg, bacterial immunoglobulin-like; MALDI-TOF, matrix-assisted laser desorption ionization time-of-flight; EDS, energy-dispersive spectrometry; ICP-OES, inductively coupled plasma optical emission spectrometry; Fn, fibronectin; NTD, N-terminal domain; ITC, isothermal titration calorimetry; DSC, differential scanning calorimetry; MOPS, 4-morpholinepropan...