Spirochaeta coccoides sp. nov., a novel coccoid spirochete from the hindgut of the termite Neotermes castaneus

Abstract

A novel spirochete strain, SPN1, was isolated from the hindgut contents of the termite Neotermes castaneus. The highest similarities (about 90%) of the strain SPN1 16S rRNA gene sequence are with spirochetes belonging to the genus Spirochaeta, and thus, the isolate could not be assigned to the so-called termite clusters of the treponemes or to a known species of the genus Spirochaeta. Therefore, it represents a novel species, which was named Spirochaeta coccoides. In contrast to all other known validly described spirochete species, strain SPN1 shows a coccoid morphology and is immotile. The isolated strain is obligately anaerobic and ferments different mono-, di-, and oligosaccharides by forming formate, acetate, and ethanol as the main fermentation end products. Furthermore, strain SPN1 is able to grow anaerobically with yeast extract as the sole carbon and energy source. The fastest growth was obtained at 30 degrees C, the temperature at which the termites were also grown. The cells possess different enzymatic activities that are involved in the degradation of lignocellulose in the termite hindgut, such as beta-D-glucosidase, alpha-L-arabinosidase, and beta-D-xylosidase. Therefore, they may play an important role in the digestion of breakdown products from cellulose and hemicellulose in the termite gut.

FIG. 1.

Phase-contrast micrograph of whole coccoid cells (A). Electron micrograph of ultrathin section (B). The thin section shows the outer envelope (arrow) surrounding coccoid forms with loose cytoplasma and small condensed areas.

FIG. 2.

Phylogenetic tree showing the relationship of strain SPN1 to other spirochetes. The tree was constructed by using the maximum likelihood method. Bootstrap values above 50 (from 100 resamplings) are shown for each node. A sequence of Escherichia coli (accession number AE000129) was used as the outgroup (not shown). For tree construction, the 16S rRNA gene sequences of additional spirochetes were included. Cluster I, clone NkS56 AB084967, clone RFS8 AF068343, Spirochaeta caldaria M71240, Treponema azotonutricium AF320287, and Treponema primitia strain ZAS-1 AF093251; cluster II, clone HsPySp20 AB032004, clone RFS9 AF068432, clone Rs-A53 AB088895, and clone Rs-G65 AB088858. The bar indicates 5% estimated sequence divergence.