Abstract
Piscirickettsiasalmonis is an intracellular bacterial fish pathogen that causes piscirickettsiosis, a disease with numerous negative impacts in the Chilean salmon farming industry. Although transcriptomic studies of P. salmonis and its host have been performed, dual host–pathogen proteomic approaches during infection are still missing. Considering that gene expression does not always correspond with observed phenotype, and bacteriological culture studies inadequately reflect infection conditions, to improve the existing knowledge for the pathogenicity of P. salmonis, we present here a global proteomic profiling of Salmon salar macrophage-like cell cultures infected with P. salmonis LF-89. The proteomic analyses identified several P. salmonis proteins from two temporally different stages of macrophages infection, some of them related to key functions for bacterial survival in other intracellular pathogens. Metabolic differences were observed in early-stage infection bacteria, compared to late-stage infections. Virulence factors related to membrane, lipopolysaccharide (LPS) and surface component modifications, cell motility, toxins, and secretion systems also varied between the infection stages. Pilus proteins, beta-hemolysin, and the type VI secretion system (T6SS) were characteristic of the early-infection stage, while fimbria, upregulation of 10 toxins or effector proteins, and the Dot/Icm type IV secretion system (T4SS) were representative of the late-infection stage bacteria. Previously described virulence-related genes in P. salmonis plasmids were identified by proteomic assays during infection in SHK-1 cells, accompanied by an increase of mobile-related elements. By comparing the infected and un-infected proteome of SHK-1 cells, we observed changes in cellular and redox homeostasis; innate immune response; microtubules and actin cytoskeleton organization and dynamics; alteration in phagosome components, iron transport, and metabolism; and amino acids, nucleoside, and nucleotide metabolism, together with an overall energy and ATP production alteration. Our global proteomic profiling and the current knowledge of the P. salmonis infection process allowed us to propose a model of the macrophage–P. salmonis interaction.
Highlights
Microbial infections are characterized by a constant interplay between pathogen and host, with pathogens exploiting various host functions during infection and hosts reacting with appropriate defense responses [1]
We focused on the host and bacterial processes, rather than individual proteins altered during infection, to discover the defense mechanism of Atlantic salmon against P. salmonis invasion, P. salmonis induced changes in the host, potential bacterial virulence factors, and their target in host cells
To standardize the infection conditions, P. salmonis growth was evaluated in liquid culture medium at different temperatures (Figure 1), including the normal temperature of bacterial growth (18 ◦C), the temperatures used for growth and infection of SHK-1 cells (20 ◦C and 16 ◦C respectively), and a higher temperature (23 ◦C)
Summary
Microbial infections are characterized by a constant interplay between pathogen and host, with pathogens exploiting various host functions during infection and hosts reacting with appropriate defense responses [1]. Transcriptomic analyses have provided evidence of host cellular processes and particular genes targeted during P. salmonis infection to promote intracellular survival and replication [7,11,12,13] These analyses contributed to a better understanding of the in vivo infection process, since genes expressed in this condition can reveal the pathogen’s survival strategy in the intracellular environment. The combination of proteomics with other omics approaches has expanded the repertoire of tools to study pathogen infections [15] Identification of these host–pathogen protein interactions in the context of infection can be critical to understand the biology of infection and to discover novel targets for treatments against microbial pathogens. We focused on the host and bacterial processes, rather than individual proteins altered during infection, to discover the defense mechanism of Atlantic salmon against P. salmonis invasion, P. salmonis induced changes in the host, potential bacterial virulence factors, and their target in host cells
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
