Chemotactic response to formate by Campylobacter concisus and its potential role in gingival colonization

Cells of Campylobacter concisus 288 were chemotactic toward formate, but not to any other compound tested. Chemicals that were not chemoattractants included 20 sugars, inorganic salts, amino acids, and their derivatives, purines and pyrimidines, fatty acids, and natural mixtures such as saliva, serum, crevicular fluid, and mucin. Chemotaxis was measured quantitatively by a modification of the capillary method. Cells were suspended in 0.01 M Tris buffer, pH 7.5, supplemented with 5 mM KCl, 0.1% Na2S2O3, and 0.1 mM dithiothreitol. Whole, parotid, and submandibular salivas were also suitable as chemotaxis buffers. Optimum response (0.4 X 10(6) to 1.5 X 10(6) cells per capillary) for chemotaxis occurred with 5 X 10(-2) M formate at 30 degrees C for 60 min. At 5 to 15 degrees C, cells were motile, but chemotaxis was not detected. Glutamine, asparagine, homoserine, and methionine inhibited formate chemotaxis at threshold concentrations of 0.1 to 1.0 mM, whereas the threshold for all other amino acids tested was 50 mM. Sugars and fatty acids at concentrations up to 0.1 M did not inhibit formate chemotaxis. C. concisus 484, Wolinella recta 371, W. curva VPI 9584, and W. succinogenes 602 were also chemotactic to formate, but C. fetus subsp. jejuni VPI H641 and C. fetus subsp. intestinalis VPI 1176 were not. Motile bacteria harvested directly from subgingival plaque were also chemotactic to formate and, to a lesser extent, lactate. Selected sugars, other fatty acids, and amino acids did not serve as chemoattractants for these plaque bacteria.

Treponema saccharophilum sp. nov., a large pectinolytic spirochete from the bovine rumen

A large, obligately anaerobic spirochete (strain PB) was isolated from bovine rumen fluid by a procedure involving rifampin as a selective agent. The helical cells measured 0.6 to 0.7 micron by 12 to 20 micron and possessed approximately 16 periplasmic flagella inserted near each end of the protoplasmic cylinder. The periplasmic flagella were arranged in a bundle wound around the cell body. Strain PB utilized as fermentable substrates various plant polysaccharides (e.g., pectin, arabinogalactan, starch, and inulin) as well as pentoses, hexoses, disaccharides, and uronic acids. Glucose was fermented to acetate, formate, and ethanol, whereas the fermentation of pectin or glucuronic acid yielded only acetate and formate as major end products. Determinations of radioactivity in end products and assays of enzymatic activities indicated that strain PB catabolized glucose via the Embden-Meyerhof pathway. Extracts of cells grown in pectin-containing media possessed relatively high levels of phospho-2-keto-3-deoxygluconate aldolase activity, an enzymatic activity typical of the Entner-Doudoroff pathway. The guanine-plus-cytosine content of the DNA of strain PB (54 mol%) was considerably higher than that of known host-associated anaerobic spirochetes. This study indicates that strain PB represents a new species of Treponema, for which we propose the name Treponema saccharophilum.

Physiological diversity of rumen spirochetes

Bovine rumen fluid contained relatively large numbers of spirochetes capable of fermenting polymers commonly present in plant materials. Polymers such as xylan, pectin, and arabinogalactan served as fermentable substrates for the spirochetes, whereas cellulose did not. Furthermore, spirochetes cultured from rumen fluid utilized as growth substrates hydrolysis products of plant polymers (e.g., D-xylose, L-arabinose, D-galacturonic acid, D-glucuronic acid, cellobiose), but did not ferment amino acids. Viable cell counts of spirochetes capable of fermenting individual plant polymers or their hydrolysis products yielded minimum values ranging from 0.2 X 10(6) to 4 X 10(6) cells per ml of rumen fluid. Thirteen strains of rumen spirochetes were characterized in terms of their fermentation products from glucose, the guanine plus cytosine content of their DNA, their ultrastructure, and their ability to ferment pectin, starch, or arabinogalactan. Of the 13 strains, 6 fermented glucose mainly to formate, acetate, and succinate, whereas the remaining 7 strains did not produce succinate, but instead formed ethanol, in addition to formate and acetate. The succinate-forming strains had two periplasmic (axial) fibrils per cell, measured 0.2 to 0.3 by 5 to 8 micrograms, had a guanine plus cytosine content of the DNA ranging from 36 to 38 mol%, and lacked the ability to ferment pectin, starch, or arabinogalactan. The ethanol-forming strains had from 8 to more than 32 periplasmic fibrils per cell, tended to be larger in cell size than the succinate-forming strains, and had a guanine plus cytosine content of the DNA ranging from 41 to 54 mol%. Some of the ethanol-forming strains fermented pectin, starch, or arabinogalactan. The results of this study indicate that the bovine rumen is inhabited by a physiologically and morphologically diverse population of spirochetes. It is likely that these spirochetes contribute significantly to the degradation of plant materials ingested by the ruminants.

Involvement of periplasmic fibrils in motility of spirochetes

Nonmotile (Mot-) strains of Spirochaeta aurantia and Spirochaeta halophila were isolated with a procedure involving mutagenesis of motile wild-type cells. Electron microscopy showed that a Mot- mutant strain of S. halophia possessed incomplete periplasmic fibrils, inasmuch as most or all of the filamentous portion of the periplasmic fibrils was absent. Some of the cells of this Mot-, fibril-defective mutant strain lacked the filamentous portion of the periplasmic fibrils and formed proximal hooks, whereas other cells appeared to have a very small segment of the filamentous portion of the periplasmic fibrils attached to the proximal hooks. Motile revertants were isolated repeatedly from cultures of the Mot-, fibril-defective mutant and from S. halophila Mot- mutants that completely lacked periplasmic fibrils. The motile revertants possessed periplasmic fibrils ultrastructurally indistinguishable from wild-type periplasmic fibrils. This study indicates that periplasmic fibrils play an essential role in the motility of spirochetes.