Actinobacillus seminis DnaK interacts with bovine transferrin, lactoferrin, and hemoglobin as a putative iron acquisition mechanism

Ovine epididymitis, caused by Actinobacilus seminis, is an infectious disease that produces atrophy of the testis, low fertility, and sterility in infected animals. Iron is a microelement necessary for different vital functions in all organisms and most microorganisms. A. seminis iron acquisition mechanisms are undiscovered. For this reason, this work aimed to know the mechanisms this bacterium possesses to respond when grown in an iron restriction culture medium. A. seminis up-expressed three proteins, including a transferrin binding protein, and down-expressed seven (enzymes and putative adhesins) proteins when grown with 2,2'dipyridyl. With chelate, its growth was reduced by 40%, but it was recovered by adding 50-µM FeCl₃. No siderophore production was detected with the CAS-BHI medium assay, but siderophore transporter proteins are present. Under normal growth conditions, this microorganism expresses a protein of 70 kDa, identified by mass spectrometry as DnaK. A. seminis DnaK interacts with biotin-labeled transferrin, lactoferrin, or bovine hemoglobin but not with biotin-labeled apo-transferrin or apo-lactoferrin, suggesting its participation in iron acquisition. This protein diminished its expression in iron restriction conditions at 37 °C but remained unchanged at 40 °C, and it is immune recognized by sheep serum with epididymitis. These different iron acquisition mechanisms could give rise to A. seminis, infecting different host tissues.