Discovery of novel treponeme bacteria
Understanding the cause of a disease is required to conduct surveillance, develop reliable diagnostic tests, and design management interventions. Research in our lab at Washington State University (WSU) and by other investigators has shown that elk hoof disease is a transmissible bacterial disease. Spiral shaped bacteria in the genus Treponema are consistently detected in the hoof lesions along with a few other types of bacteria that also appear to be associated with the disease.
In research recently published in the journal Applied and Environmental Microbiology, our team at WSU used cutting-edge technology to discover new variants and apparent species of Treponema and Treponeme-like bacteria from elk with hoof disease.
Traditionally, bacteria associated with diseases have been studied following growth and isolation in nutrient gel under controlled laboratory conditions (called bacterial culture). But not all bacteria grow in the lab due to their need for very specific nutrients or environmental conditions.
Unfortunately, this is the case with Treponema bacteria, so only a couple of species have been cultured for identification and characterization.
DNA sequencing of small portions of bacterial genomes indicates that more Treponema or Treponema-like bacteria exist but they have yet to be cultured and fully identified. Technology now provides an alternative approach to identify these stealthy bacteria using an approach called metagenome assembly of genomes from shotgun sequences.
Dr. Sushanta Deb, a postdoctoral fellow studying elk hoof disease in our lab at WSU, used this technique to discover new bacteria associated with elk hoof disease. Dr. Deb was able to construct the genomes of three novel bacteria from millions of snippets of DNA in samples from elk hooves. Assembling a genome is like putting together pieces of a puzzle without a picture, and in this case where many other bacteria are also present in the sample, it is like putting together one puzzle mixed in with pieces from a hundred other puzzles.
Dr. Deb, supported by faculty mentor Dr. Devendra Shah (previously at WSU and now at Texas Tech University), used specialized expertise to apply a unique suite of complex computer programs to analyze the data and confirm the results. He constructed genomes that matched with two previously reported Treponema species that were cultured in a lab (Treponema pedis and Treponema phagedenis). However, the bacteria contained minor variations that suggest they are unique to elk or to the geographic area.
In an exciting finding, Dr. Deb also constructed genomes of three new types of bacteria that are in the genus Treponema or a yet unknown Treponema-like genus. These represent newly discovered bacteria that have not previously been described or cultured.
More investigation is needed, and is underway, to understand the role that these novel bacteria play in elk hoof disease. However, based on their consistent detection in the small number of elk hooves examined to date, we suspect that multiple Treponema, both previously known and newly discovered, are likely involved in lesion development. We are also applying the technique to detect novel bacteria other than Treponema that appear to be associated with the disease.
Margaret A. Wild, DVM, PhD
Veterinary Microbiology and Pathology
margaret.wild@wsu.edu