Abstract
Treponema pedis and T. denticola are two genetically related species with different origins of isolation. Treponema denticola is part of the human oral microbiota and is associated with periodontitis while T. pedis has been isolated from skin lesions in animals, e.g., digital dermatitis in cattle and necrotic ulcers in pigs. Although multiple Treponema phylotypes may exist in ulcerative lesions in pigs, T. pedis appears to be a predominant spirochete in these lesions. Treponema pedis can also be present in pig gingiva. In this study, we determined the complete genome sequence of T. pedis strain T A4, isolated from a porcine necrotic ear lesion, and compared its genome with that of T. denticola. Most genes in T. pedis were homologous to those in T. denticola and the two species were similar in general genomic features such as size, G+C content, and number of genes. In addition, many homologues of specific virulence-related genes in T. denticola were found in T. pedis. Comparing a selected pair of strains will usually not give a complete picture of the relatedness between two species. We therefore complemented the analysis with draft genomes from six T. pedis isolates, originating from gingiva and necrotic ulcers in pigs, and from twelve T. denticola strains. Each strain carried a considerable amount of accessory genetic material, of which a large part was strain specific. There was also extensive sequence variability in putative virulence-related genes between strains belonging to the same species. Signs of lateral gene-transfer events from bacteria known to colonize oral environments were found. This suggests that the oral cavity is an important habitat for T. pedis. In summary, we found extensive genomic similarities between T. pedis and T. denticola but also large variability within each species.
Highlights
The genus Treponema includes commensal and pathogenic spirochete species, some of which affect human and animal health
Our research focuses on characterization of porcine skin lesions that are colonized, and perhaps worsened, by Treponema [1,2,3]
T. pedis has been isolated from gingiva and necrotic ulcers, referred to as ear necrosis and shoulder ulcers [2,3]
Summary
The genus Treponema includes commensal and pathogenic spirochete species, some of which affect human and animal health. These fastidious bacteria often require an anaerobic environment and are difficult to grow and manipulate in vitro. E.g. T_pallidum, are host dependent and have not been successfully cultivated on bacteriological media. The fastidiousness of these bacteria has hampered Treponema research. T. pedis has been isolated from gingiva and necrotic ulcers, referred to as ear necrosis and shoulder ulcers [2,3]. Ear necrosis and shoulder ulcers are necrotic skin lesions of animal welfare concern. Common coccoid bacteria in skin lesions in pigs are Staphylococcus hyicus and b-hemolytic streptococci [5]
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