Genome sequencing of Moxarella bovis Doors open for new interventions against ‘Pinkeye’ in cattle
NEBRASKA, October 25, 2022 — Scientists have revealed that there are two different variants or genotypes of Moraxella bovis (M.bovis), a bacterium known to cause conjunctivitis in cattle. This discovery helps scientists understand how different types of M. bovis cause infection in livestock and can help develop preventative measures to protect US livestock from this disease.
Bovine conjunctivitis, or infectious bovine keratoconjunctivitis, is a highly contagious eye infection that causes redness, itching, pain and discomfort in the eyes of affected animals. Severe cases can lead to blindness and adversely affect weight gain in calves, and are therefore an animal welfare concern and have negative economic impacts on the beef industry.
Scientists from the USDA Agricultural Research Service (ARS) and the University of Nebraska-Lincoln (UNL) sequenced and compared the genomes of a collection of M bovis variants and found that they consisted of two major genotypes. They identified DNA differences between genotypes. Additionally, they found substances that can potentially be used as targets to control the disease.
“We found major differences in virulence factors between the two genotypes,” said Emily Wynn, ARS research microbiologist. “For instance, M.bovis has a toxin, called hemolysin toxin, which it uses to enter the eye. We found that the two genotypes have different versions of the toxin. This difference and others among the collection of M.bovis variants could mean that there are variations in their ability to cause disease.
In addition, scientists have identified proteins (substances) located on the outer membrane of the bacterial cell.
The specific location of these proteins makes them available to the host immune system as they are located on the outer membrane. Proteins that are unique to one or both genotypes can be used as targets to develop specific preventive actions against one of the genotypes, if needed,” Wynn added.
This is important because for years scientists have been closely studying another substance in this bacterium to develop disease interventions, called pilin proteins. Pilins facilitate the fixation of M.bovis at the eye. However, using pilins to develop interventions could be tricky.
The pilin gene of M.bovis can undergo a reversal,” said Mike ClawsonARS research molecular biologist at the US Meat Animal Research Center in Clay Center, NE. “This is where parts of the gene turn around and are rearranged on the bacterial chromosome. As a result, a newly formed pilin gene is created which encodes a new protein version of itself, which helps M.bovis avoid recognition by the immune system. Pilin gene inversions are thought to be a relatively rare process. However, we have seen evidence that several M.bovis strains underwent the inversions during our study. This makes the pilin gene a challenge to use as a target and underscores why the outer membrane proteins identified in this study are an important finding.
The team sequenced M.bovis strains isolated from cattle from seventeen U.S. states and one Canadian province that were assembled by Dustin LoyUNL professor and veterinary diagnostic microbiologist.
“The first finished genome of M.bovis was produced by this collaboration on an experimental strain in 2018“, Loy said. “Since then, we have not seen much progress in the complete sequencing of this bacterium until this study between the ARS and the UNL.
Loy has devoted years of research to understanding this infectious disease, collecting samples directly from veterinarians working with cattle, to test and identify variability between strains.
This disease is often overlooked. Yet it is the most commonly reported disease in beef cows and the second most commonly reported in calves. Our work recognizes the economic impact this causes to beef producers,” Loy added.
The team commemorates collaborative pinkeye research that dates back approximately 58 years with the groundbreaking work of ARS researcher George Washington Pugh Jr., who was the agency’s first black scientist and made major strides in understanding the role of M. bovis in pink eyes. More recently, the UNL published a collaborative study with ARS evaluating the immunological responses and the efficacy of vaccines to protect cattle against diseases associated with these bacteria.
The recent study was published in BMC Microbiology by Emily L. Wynn (ARS), Matthew M Hille (UNL), John Dustin Loy (UNL), Gennie Schuller (ARS), Kristen L Kuhn (ARS), Aaron M Dickey (ARS), James L Bono (ARS) and Michael L Clawson (ARS).
The Agricultural Research Service is the principal internal scientific research agency of the United States Department of Agriculture. Daily, ARS focuses on solutions to agricultural problems affecting America. Every dollar invested in agricultural research in the United States has an economic impact of $20.
–USDA Agricultural Research Service