A single point mutation in the hyaC gene affects Pasteurella multocida serovar A capsule production and virulence.

Pasteurella multocida (P. multocida) is a Gram-negative bacterium which causes diseases in poultry, livestock, and humans, resulting in huge economic losses. P. multocida serovar A CQ6 (PmCQ6) is a naturally occurring attenuated strain with a thin capsule. Thus, we aimed to explore why this strain is less virulent and produces less capsule compared with P. multocida serovar A strain CQ2 (PmCQ2). Analysis of capsular polysaccharide synthesis genes in PmCQ6 revealed that, compared with PmCQ2, there was only a single point mutation in the initiation codon sequence of the hyaC gene. To test whether this point mutation caused capsular deficiency and reduced virulence, we rescued this hyaC mutation and observed a restoration of capsule production and higher virulence. Transcriptome analysis showed that the hyaC point mutation led to a downregulation of capsule synthesis and/or iron utilization related-genes. Taken together, the results indicate that the start codon mutation of hyaC is an important factor affecting the capsule synthesis and virulence of PmCQ6.

Transcriptomic Analysis of High- and Low-Virulence Bovine Pasteurella multocida in vitro and in vivo.

Pasteurella multocida is a gram-negative opportunistic pathogen that causes various diseases in poultry, livestock, and humans, resulting in huge economic losses. Pasteurella multocida serotype A CQ6 (PmCQ6) is a naturally occurring attenuated strain, while P. multocida serotype A strain CQ2 (PmCQ2) is a highly virulent strain isolated from calves. Compared with PmCQ2, it was found that bacterial loads and tissue lesions of lung tissue significantly decreased and survival rates significantly improved in mice infected with PmCQ6 by intranasal infection. However, comparative genome analysis showed that the similarity between the two strains is more than 99%. To further explore the virulence difference mechanism of PmCQ2 and PmCQ6, transcriptome sequencing analysis of the two strains was performed. The RNA sequencing analysis of PmCQ2 and PmCQ6 showed a large number of virulence-related differentially expressed genes (DEGs) in vivo and in vitro. Among them, 38 virulence-related DGEs were significantly up-regulated due to PmCQ6 infection, while the number of PmCQ2 infection was 46, much more than PmCQ6. In addition, 18 virulence-related DEGs (capsule, iron utilization, lipopolysaccharide, and outer membrane protein-related genes) were up-regulated in PmCQ2 infection compared to PmCQ6 infection, exhibiting a higher intensive expression level in vivo. Our findings indicate that these virulence-related DEGs (especially capsule) might be responsible for the virulence of PmCQ2 and PmCQ6, providing prospective candidates for further studies on pathogenesis.