Stress Tolerance-Related Genetic Traits of Fish Pathogen Flavobacterium psychrophilum in a Mature Biofilm

Abstract

Flavobacterium psychrophilum is the causative agent of bacterial cold-water disease and rainbow trout fry syndrome, and hence this bacterium is placed among the most important salmonid pathogens in the freshwater aquaculture industry. Since bacteria in biofilms differ substantially from free-living counterparts, this study sought to find the main differences in gene expression between sessile and planktonic states of F. psychrophilum LM-02-Fp and NCMB1947T, with focus on stress-related changes in gene expression occurring during biofilm formation. To this end, biofilm and planktonic samples were analyzed by RNA sequencing to detect differentially expressed candidate genes (DECGs) between the two growth states, and decreasing the effects of interstrain variation by considering only genes with log2-fold changes ≤ −2 and ≥ 2 at Padj-values ≤ 0.001 as DECGs. Overall, 349 genes accounting for ~15% of total number of genes expressed in transcriptomes of F. psychrophilum LM-02-Fp and NCMB1947T (n = 2327) were DECGs between biofilm and planktonic states. Approximately 83 and 81% of all up- and down-regulated candidate genes in mature biofilms, respectively, were assigned to at least one gene ontology term; these were primarily associated with the molecular function term “catalytic activity.” We detected a potential stress response in mature biofilms, characterized by a generalized down-regulation of DECGs with roles in the protein synthesis machinery (n = 63, primarily ribosomal proteins) and energy conservation (seven ATP synthase subunit genes), as well as an up-regulation of DECGs involved in DNA repair (ruvC, recO, phrB1, smf, and dnaQ) and oxidative stress response (cytochrome C peroxidase, probable peroxiredoxin, and a probable thioredoxin). These results support the idea of a strategic trade-off between growth-related processes and cell homeostasis to preserve biofilm structure and metabolic functioning. In addition, LDH-based cytotoxicity assays and an intraperitoneal challenge model for rainbow trout fry agreed with the transcriptomic evidence that the ability of F. psychrophilum to form biofilms could contribute to the virulence. Finally, the reported changes in gene expression, as induced by the plankton-to-biofilm transition, represent the first transcriptomic guideline to obtain insights into the F. psychrophilum biofilm lifestyle that could help understand the prevalence of this bacterium in aquaculture settings.

Improved understanding of biofilm development by Piscirickettsia salmonis reveals potential risks for the persistence and dissemination of piscirickettsiosis

“…This result should not be extrapolated to in vivo infection cases of salmonids or other bacterial species. For instance, another study that used Flavobacterium psychrophilum and the CHSE-214 cell line demonstrated higher virulence in the biofilm state than in the planktonic state 47 . However, the aforementioned lack of differences in P. salmonis-induced cytotoxicity between www.nature.com/scientificreports/ biofilm-derived and planktonic bacteria has also been found when infecting the CHSE-214 cell line with P. salmonis LF-89 T and CA5 (results from another yet-unpublished study by our team).…”

“…This result should not be extrapolated to in vivo infection cases of salmonids or other bacterial species. For instance, another study that used Flavobacterium psychrophilum and the CHSE-214 cell line demonstrated higher virulence in the biofilm state than in the planktonic state 47 . However, the aforementioned lack of differences in P .…”

Biosynthesis and Antimicrobial Activity of Pseudodesmin and Viscosinamide Cyclic Lipopeptides Produced by Pseudomonads Associated with the Cocoyam Rhizosphere

“…Pseudomonas cyclic lipopeptides (or CLPs) are surface-active metabolites synthesized non-ribosomally by modular multifunctional enzymes named non-ribosomal peptide synthetases (NRPSs) [ 1 ]. Structurally, CLPs comprise a cyclic oligopeptide lactone ring linked to a fatty acid tail [ 2 ]. These molecules mediate multiple biological functions, including biofilm formation, swarming motility, virulence (in plant pathogenic strains), antibacterial, antifungal, anti-oomycete, insecticidal, anti-carcinogenic and antiviral properties [ 2 , 3 , 4 , 5 , 6 , 7 ].…”

“…Structurally, CLPs comprise a cyclic oligopeptide lactone ring linked to a fatty acid tail [ 2 ]. These molecules mediate multiple biological functions, including biofilm formation, swarming motility, virulence (in plant pathogenic strains), antibacterial, antifungal, anti-oomycete, insecticidal, anti-carcinogenic and antiviral properties [ 2 , 3 , 4 , 5 , 6 , 7 ]. These bioactive molecules are produced by specific species within the P. syringae complex, P. fluorescens, P. putida and P. asplenii groups [ 8 ].…”

“…Pseudomonas CLPs are structurally divided into 14 distinct groups [ 2 ]. From a chemical point of view, determinants of the structural variation of CLPs include overall sequence length (number of amino acids), macrocycle length and amino acid composition [ 2 , 9 ].…”