Purification of polysaccharide antigen from Leptospira biflexa strain Urawa

Transcriptome Sequencing Reveals Wide Expression Reprogramming of Basal and Unknown Genes in Leptospira biflexa Biofilms

In this work, we describe the first transcriptome based on RNA-seq technology focused on studying transcriptional changes associated with biofilm growth in a member of the genus Leptospira. As many pathogenic species of this genus can survive inside the host but also persist in environmental water, mostly forming biofilms, identifying the molecular basis of this capacity can impact the understanding of how leptospires are able to fulfill a complete life cycle that alternates between adaptation to the host and adaptation to hostile external environmental conditions. We identified several genes and regulatory networks that can be the kickoff for deepening understanding of the molecular mechanisms involving bacterial persistence via biofilm formation; understanding this is important for the future development of tools for controlling leptospirosis.

The genus Leptospira is composed of pathogenic and saprophytic spirochetes. Pathogenic Leptospira is the etiological agent of leptospirosis, a globally spread neglected disease. A key ecological feature of some pathogenic species is their ability to survive both within and outside the host. For most leptospires, the ability to persist outside the host is associated with biofilm formation, a most important bacterial strategy to face and overcome hostile environmental conditions. The architecture and biochemistry of leptospiral biofilms are rather well understood; however, the genetic program underpinning biofilm formation remains mostly unknown. In this work, we used the saprophyte Leptospira biflexa as a model organism to assess over- and underrepresented transcripts during the biofilm state, using transcriptome sequencing (RNA-seq) technology. Our results showed that some basal biological processes like DNA replication and cell division are downregulated in the mature biofilm. Additionally, we identified significant expression reprogramming for genes involved in motility, sugar/lipid metabolism, and iron scavenging, as well as for outer membrane-encoding genes. A careful manual annotation process allowed us to assign molecular functions to many previously uncharacterized genes that are probably involved in biofilm metabolism. We also provided evidence for the presence of small regulatory RNAs in this species. Finally, coexpression networks were reconstructed to pinpoint functionally related gene clusters that may explain how biofilm maintenance is regulated. Beyond elucidating some genetic aspects of biofilm formation, this work reveals a number of pathways whose functional dissection may impact our understanding of leptospiral biology, in particular how these organisms adapt to environmental changes.

IMPORTANCE In this work, we describe the first transcriptome based on RNA-seq technology focused on studying transcriptional changes associated with biofilm growth in a member of the genus Leptospira. As many pathogenic species of this genus can survive inside the host but also persist in environmental water, mostly forming biofilms, identifying the molecular basis of this capacity can impact the understanding of how leptospires are able to fulfill a complete life cycle that alternates between adaptation to the host and adaptation to hostile external environmental conditions. We identified several genes and regulatory networks that can be the kickoff for deepening understanding of the molecular mechanisms involving bacterial persistence via biofilm formation; understanding this is important for the future development of tools for controlling leptospirosis.

Occurrence of [--> 3)-beta-D-Manp-(1 --> 4)-beta-D-Manp-(1 -->]n units in the antigenic polysaccharides from Leptospira biflexa serovar patoc strain Patoc I

In this study, we isolated three kinds of antigenic polysaccharide components (tentatively designed as AP-1-3) from cells of Leptospira biflexa serovar patoc strain Patoc I (L. biflexa patoc Patoc I) by the hot phenol-water procedure, followed by treatment with mild acid and column chromatography. Two of them (AP-1 and AP-2) were recovered from the phenol-soluble fraction whereas another (AP-3) was recovered from the aqueous fraction. All of them reacted toward an anti-L. biflexa serum and also cross-reacted in similar extents toward most of the other leptospiral antisera tested. Such immunoreactions were specifically inhibited by a beta-(1 --> 4)-linked mannobiose, but were not by any mono- and oligosaccharide tested. From their structural analyses including 1H and 13C NMR spectrometry, Smith degradation and methylation analysis, it was revealed that all of these antigenic polysaccharides had the same disaccharide unit --> 3)-beta-D-Manp-(1 --> 4)-beta-D-Manp-(1 --> in their major polysaccharide parts, but they differed in the acyl substituents. Therefore it is most likely that such mannobiose unit is a candidate for the antigenic epitopes of L. biflexa polysaccharides.

Chemical compositions of cell walls and polysaccharide fractions of spirochetes

Cellular polysaccharide fractions of various representative members of genera of the family Spirochaetaceae were obtained by the ammonium hydroxide extraction method. The sugar composition of the polysaccharide preparations was complex and many kinds of sugars such as rhamnose, fucose, ribose, xylose, mannose, galactose, and glucose were detected in all of the spirochetes tested. Of particular interest was the presence of 4-O-methylmannose as a constituent polysaccharide in members of the genus Leptospira. This sugar was not detected in the polysaccharides of Spirochaeta, Borrelia, and Treponema. The chemical compositions of cell wall fractions were also examined. 4-O-Methylmannose was detected in the cell wall polysaccharides of the genus Leptospira but not in cell walls prepared from the Spirochaeta, Borrelia, and Treponema. The diaminopimelic acid present in cell wall peptidoglycans of the genus Leptospira was meso-diaminopimelic acid (A2pm). The molar ratios of alanine, glutamic acid, A2pm, glycine, muramic acid, and glucosamine in leptospiral cell walls were found to be approximately 2:1:1:1:1:1. In contrast to the Leptospira, the peptidoglycans of genera Spirochaeta, Borrelia, and Treponema contained ornithine (Orn) but not A2pm. Since 4-O-methylmannose and A2pm were found in the cell wall fractions of genus Leptospira but not in Spirochaeta, Borrelia, or Treponema, it was suggested that the chemical compositions of the cell wall might become an important criterion for the chemotaxonomy of Spirochaetales.

Sugar synthesis in Leptospira. I. Presence of glucosephosphate isomerase

The presence of glucosephosphate isomerase, one of the key enzymes in carbohydrate metabolism, was confirmed for the first time in the cell-free extract of Leptospira biflexa. The glucosephosphate isomerase of L. biflexa was heat-labile and its optimum pH was about 8.5. The enzyme showed an optimal temperature of about 45 C but was more stable at 30 C. Km value of the enzyme was 5.6 X 10(-3)M. The activity of the enzyme was inhibited by the inhibitor, 6-phosphogluconate. From this study, the presence of a metabolic pathway, the phosphogluconate pathway, other than non-oxidative pentose phosphate pathway presented by Baseman and Cox was suggested.

Occurrence of 3-O-methylmannose in the polysaccharide of Leptospira biflexa Urawa

3-O-methylmannose was identified by gas-liquid chromatography-mass spectrometry in the acid hydrolysate of the polysaccharide of Leptospira biflexa Urawa.

[Study of a specific polyoside and a group antigen extracted from Leptospira biflexa patoc, patoc I strain]

We extracted from L. biflexa patoc a fraction F, reacting in hemagglutination and ring tests with sera prepared against more than ten different serogroups. This fraction contains mainly a polysaccharide (65 per cent), the role of which was clearly demonstrated in the precipitation reaction with homologous antisera, through periodic oxidation; it also contains lipids (20 per cent) and proteins (10 per cent). We isolated from this fraction F, by Biogel column chromatography, 2 distinct antigens, one, F2, carrying the patoc-type specificity, the other, F 1B, a group specificity shared by many leptospira. These antigens differ not only immunogically, but also in their chemical composition. The type-specific antigen F2 contains mainly a polysaccharide composed of arabinose and glucosamine (possibly an immunodominant sugar). As for the group-specific fraction F 1B, its composition is more complex since lipids and proteins are also found with the polysaccharide. This antigen could therefore be a lipoglycoprotein.

Chemical studies on the cell walls of Leptorspira biflexa strain Urawa and Treponema pallidum strain Reiter

The preparation and chemical properties of the cell walls of Leptospira biflexa Urawa and Treponema pallidum Reiter are described. Both cell walls are composed mainly of polysaccharides and peptidoglycans. The data of chemical analysis indicate that the cell wall of L. biflexa Urawa contains rhamnose, arabinose, xylose, mannose, galactose, glucose and unidentified sugars as neutral sugars, and alanine, glutamic acid, alpha, epsilon-diaminopimelic acid, glucosamine and muramic acid as major amino acids and amino sugars. As major chemical constituents of the cell wall of T. pallidum Reiter, rhamnose, arabinose, xylose, mannose, galactose, glucose, alanine, glutamic acid, ornithine, glycine, glucosamine and muramic acid have been detected. The chemical properties of protein and polysaccharide fractions prepared from the cells of T. pallidum Reiter were also partially examined.