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°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 ␤-D-glucosidase, ␣-L-arabinosidase, and ␤-D-xylosidase. Therefore, they may play an important role in the digestion of breakdown products from cellulose and hemicellulose in the termite gut.Spirochetes are distinguished from all other bacteria by their unique morphology and mechanism of motility due to the helical shape of the cells and the location of the flagella (axial filaments). They form a coherent phylogenetic group at the phylum level. These axial filaments, ultrastructurally similar to bacterial flagella, are attached to the cell poles and wrapped around the protoplasmic cylinder, which consists of the cytoplasmic and nuclear regions. The flagella and the protoplasmic cylinder are surrounded by a multilayered membrane called the outer sheath or outer cell envelope (9). Comparisons of 16S rRNA sequences demonstrate that the spirochetes represent a monophyletic phylum within the bacteria (35). Spirochetes are widespread in several environments, either as freeliving cells, mainly in marine and limnic sediments, or host associated as commensals or parasites of animals and humans.One of the spirochetal habitats is the digestive tract of termites and wood-eating cockroaches. Termites have developed a unique hindgut flora consisting of bacteria, archaea, flagellates, and yeasts. This symbiotic microbial community supports the decomposition of complex organic compounds and thus enables the termites to feed on wood or soil (6, 13, 21, 44). Spirochetes are one of the most abundant bacteria present in the gut fluid of termites, (36). Spirochetes of several sizes (3 to 100 m in length; 0.2 to 1.0 m in width) are consistently present in the hindguts of all termites (5). Whereas most spirochetes usually exist free-living in the gut fluid, they have also been found as ectosymbionts attached to the surfaces of protists, such as Mixotricha paradoxa, that inhabit the gut of the lower wood-eating termite Mastotermes darwinien...

Genome Shrinkage and Loss of Nutrient-Providing Potential in the Obligate Symbiont of the Primitive Termite Mastotermes darwiniensis

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Acetogenesis from H2plus CO2and nitrogen fixation by an endosymbiotic spirochete of a termite-gut cellulolytic protist

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Cellulolytic activity and structure of symbiotic bacteria in locust guts

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