The Actinobacillus pleuropneumoniae sulfate-binding protein is required for the acquisition of sulfate and methionine, but is not essential for virulence

Abstract

Actinobacillus pleuropneumoniae is a Gram-negative pathogen that causes porcine pleuropneumonia, an infectious disease responsible for significant losses in the pig industry. Sulfur is an essential nutrient that is widely required by microorganisms; however, the mechanism involved in A. pleuropneumoniae sulfur transport is unknown. In this study, we showed that a periplasmic protein predicted to be involved in sulfur acquisition (sulfate-binding protein (Sbp)), is required for A. pleuropneumoniae growth in chemically defined medium (CDM) containing sulfate or methionine as the sole sulfur sources. However, utilization of glutathione and cysteine was not affected in the sbp-deletion mutant. The virulence of A. pleuropneumoniae in mice was not affected by the absence of Sbp. Moreover, we demonstrated that Sbp was not essential for the in vivo colonization of A. pleuropneumoniae in mice or pigs. Collectively, these findings reveal that A. pleuropneumoniae Sbp plays an important role in the acquisition of the sulfur nutrients, sulfate and methionine. The presence of other sulfur uptake systems suggests A. pleuropneumoniae has multiple functionally redundant pathways ensuring uptake of important nutrients during infection.