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Pulgar R, Hödar C, Travisany D, Zuñiga A, Domínguez C, Maass A, González M, Cambiazo V. Transcriptional response of Atlantic salmon families to Piscirickettsia salmonis infection highlights the relevance of the iron-deprivation defence system. BMC Genomics 2015; 16:495. [PMID: 26141111 PMCID: PMC4490697 DOI: 10.1186/s12864-015-1716-9] [Citation(s) in RCA: 56] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2014] [Accepted: 06/23/2015] [Indexed: 01/24/2023] Open
Abstract
Background Piscirickettsiosis or Salmonid Rickettsial Septicaemia (SRS) is a bacterial disease that has a major economic impact on the Chilean salmon farming industry. Despite the fact that Piscirickettsia salmonis has been recognized as a major fish pathogen for over 20 years, the molecular strategies underlying the fish response to infection and the bacterial mechanisms of pathogenesis are poorly understood. We analysed and compared the head kidney transcriptional response of Atlantic salmon (Salmo salar) families with different levels of susceptibility to P. salmonis infection in order to reveal mechanisms that might confer infection resistance. Results We ranked forty full-sibling Atlantic salmon families according to accumulated mortality after a challenge with P. salmonis and selected the families with the lowest and highest cumulative mortalities for microarray gene expression analysis. A comparison of the response to P. salmonis infection between low and high susceptibility groups identified biological processes presumably involved in natural resistance to the pathogen. In particular, expression changes of genes linked to cellular iron depletion, as well as low iron content and bacterial load in the head kidney of fish from low susceptibility families, suggest that iron-deprivation is an innate immunity defence mechanism against P. salmonis. To complement these results, we predicted a set of iron acquisition genes from the P. salmonis genome. Identification of putative Fur boxes and expression of the genes under iron-depleted conditions revealed that most of these genes form part of the Fur regulon of P. salmonis. Conclusions This study revealed, for the first time, differences in the transcriptional response to P. salmonis infection among Atlantic salmon families with varied levels of susceptibility to the infection. These differences correlated with changes in the abundance of transcripts encoding proteins directly and indirectly involved in the immune response; changes that highlighted the role of nutritional immunity through iron deprivation in host defence mechanisms against P. salmonis. Additionally, we found that P. salmonis has several mechanisms for iron acquisition, suggesting that this bacterium can obtain iron from different sources, including ferric iron through capturing endogenous and exogenous siderophores and ferrous iron. Our results contribute to determining the underlying resistance mechanisms of Atlantic salmon to P. salmonis infection and to identifying future treatment strategies. Electronic supplementary material The online version of this article (doi:10.1186/s12864-015-1716-9) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Rodrigo Pulgar
- Laboratorio de Bioinformática y Expresión Génica, Instituto de Nutrición y Tecnología de los Alimentos (INTA), Universidad de Chile, El Líbano 5524, Santiago, Chile.
| | - Christian Hödar
- Laboratorio de Bioinformática y Expresión Génica, Instituto de Nutrición y Tecnología de los Alimentos (INTA), Universidad de Chile, El Líbano 5524, Santiago, Chile. .,Fondap Center for Genome Regulation, Av. Blanco Encalada 2085, Santiago, Chile.
| | - Dante Travisany
- Fondap Center for Genome Regulation, Av. Blanco Encalada 2085, Santiago, Chile. .,Center for Mathematical Modeling and Department of Mathematical Engineering, Av. Beauchef 851, Santiago, Chile.
| | - Alejandro Zuñiga
- Laboratorio de Bioinformática y Expresión Génica, Instituto de Nutrición y Tecnología de los Alimentos (INTA), Universidad de Chile, El Líbano 5524, Santiago, Chile.
| | - Calixto Domínguez
- Laboratorio de Bioinformática y Expresión Génica, Instituto de Nutrición y Tecnología de los Alimentos (INTA), Universidad de Chile, El Líbano 5524, Santiago, Chile.
| | - Alejandro Maass
- Fondap Center for Genome Regulation, Av. Blanco Encalada 2085, Santiago, Chile. .,Center for Mathematical Modeling and Department of Mathematical Engineering, Av. Beauchef 851, Santiago, Chile.
| | - Mauricio González
- Laboratorio de Bioinformática y Expresión Génica, Instituto de Nutrición y Tecnología de los Alimentos (INTA), Universidad de Chile, El Líbano 5524, Santiago, Chile. .,Fondap Center for Genome Regulation, Av. Blanco Encalada 2085, Santiago, Chile.
| | - Verónica Cambiazo
- Laboratorio de Bioinformática y Expresión Génica, Instituto de Nutrición y Tecnología de los Alimentos (INTA), Universidad de Chile, El Líbano 5524, Santiago, Chile. .,Fondap Center for Genome Regulation, Av. Blanco Encalada 2085, Santiago, Chile.
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α-fur, an antisense RNA gene to fur in the extreme acidophile Acidithiobacillus ferrooxidans. Microbiology (Reading) 2014; 160:514-524. [DOI: 10.1099/mic.0.073171-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
A large non-coding RNA, termed α-Fur, of ~1000 nt has been detected in the extreme acidophile Acidithiobacillus ferrooxidans encoded on the antisense strand to the iron-responsive master regulator fur (ferric uptake regulator) gene. A promoter for α-fur was predicted bioinformatically and validated using gene fusion experiments. The promoter is situated within the coding region and in the same sense as proB, potentially encoding a glutamate 5-kinase. The 3′ termination site of the α-fur transcript was determined by 3′ rapid amplification of cDNA ends to lie 7 nt downstream of the start of transcription of fur. Thus, α-fur is antisense to the complete coding region of fur, including its predicted ribosome-binding site. The genetic context of α-fur is conserved in several members of the genus Acidithiobacillus but not in all acidophiles, indicating that it is monophyletic but not niche specific. It is hypothesized that α-Fur regulates the cellular level of Fur. This is the fourth example of an antisense RNA to fur, although it is the first in an extreme acidophile, and underscores the growing importance of cis-encoded non-coding RNAs as potential regulators involved in the microbial iron-responsive stimulon.
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Harrison A, Santana EA, Szelestey BR, Newsom DE, White P, Mason KM. Ferric uptake regulator and its role in the pathogenesis of nontypeable Haemophilus influenzae. Infect Immun 2013; 81:1221-33. [PMID: 23381990 PMCID: PMC3639608 DOI: 10.1128/iai.01227-12] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2012] [Accepted: 01/21/2013] [Indexed: 11/20/2022] Open
Abstract
Nontypeable Haemophilus influenzae (NTHi) is a commensal microorganism of the human nasopharynx, and yet is also an opportunistic pathogen of the upper and lower respiratory tracts. Host microenvironments influence gene expression patterns, likely critical for NTHi persistence. The host sequesters iron as a mechanism to control microbial growth, and yet iron limitation influences gene expression and subsequent production of proteins involved in iron homeostasis. Careful regulation of iron uptake, via the ferric uptake regulator Fur, is essential in multiple bacteria, including NTHi. We hypothesized therefore that Fur contributes to iron homeostasis in NTHi, is critical for bacterial persistence, and likely regulates expression of virulence factors. Toward this end, fur was deleted in the prototypic NTHi clinical isolate, 86-028NP, and we assessed gene expression regulated by Fur. As expected, expression of the majority of genes that encode proteins with predicted roles in iron utilization was repressed by Fur. However, 14 Fur-regulated genes encode proteins with no known function, and yet may contribute to iron utilization or other biological functions. In a mammalian model of human otitis media, we determined that Fur was critical for bacterial persistence, indicating an important role for Fur-mediated iron homeostasis in disease progression. These data provide a profile of genes regulated by Fur in NTHi and likely identify additional regulatory pathways involved in iron utilization. Identification of such pathways will increase our understanding of how this pathogen can persist within host microenvironments, as a common commensal and, importantly, as a pathogen with significant clinical impact.
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Affiliation(s)
- Alistair Harrison
- The Center for Microbial Pathogenesis, The Research Institute at Nationwide Children's Hospital, The Center for Microbial Interface Biology, and Department of Pediatrics, The Ohio State University, Columbus, Ohio, USA.
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