Stress Survival Islet 2, Predominantly Present in Listeria monocytogenes Strains of Sequence Type 121, Is Involved in the Alkaline and Oxidative Stress Responses

ABSTRACT The foodborne pathogen Listeria monocytogenes is able to survive a variety of stress conditions leading to the colonization of different niches like the food processing environment. This study focuses on the hypervariable genetic hot spot lmo0443 to lmo0449 haboring three inserts: the stress survival islet 1 (SSI-1), the single-gene insert LMOf2365_0481, and two homologous genes of the nonpathogenic species Listeria innocua: lin0464, coding for a putative transcriptional regulator, and lin0465, encoding an intracellular PfpI protease. Our prevalence study revealed a different distribution of the inserts between human and food-associated isolates. The lin0464-lin0465 insert was predominantly found in food-associated strains of sequence type 121 (ST121). Functional characterization of this insert showed that the putative PfpI protease Lin0465 is involved in alkaline and oxidative stress responses but not in acidic, gastric, heat, cold, osmotic, and antibiotic stresses. In parallel, deletion of lin0464 decreased survival under alkaline and oxidative stresses. The expression of both genes increased significantly under oxidative stress conditions independently of the alternative sigma factor σB. Furthermore, we showed that the expression of the protease gene lin0465 is regulated by the transcription factor lin0464 under stress conditions, suggesting that lin0464 and lin0465 form a functional unit. In conclusion, we identified a novel stress survival islet 2 (SSI-2), predominantly present in L. monocytogenes ST121 strains, beneficial for survival under alkaline and oxidative stresses, potentially supporting adaptation and persistence of L. monocytogenes in food processing environments. IMPORTANCE Listeria monocytogenes strains of ST121 are known to persist for months and even years in food processing environments, thereby increasing the risk of food contamination and listeriosis. However, the molecular mechanism underlying this remarkable niche-specific adaptation is still unknown. Here, we demonstrate that the genomic islet SSI-2, predominantly present in L. monocytogenes ST121 strains, is beneficial for survival under alkaline and oxidative stress conditions, which are routinely encountered in food processing environments. Our findings suggest that SSI-2 is part of a diverse set of molecular determinants contributing to niche-specific adaptation and persistence of L. monocytogenes ST121 strains in food processing environments.

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Histone Deacetylase HDA-2 Regulates Trichoderma atroviride Growth, Conidiation, Blue Light Perception, and Oxidative Stress Responses

Applied and Environmental Microbiology ◽

10.1128/aem.02922-16 ◽

2016 ◽

Vol 83 (3) ◽

Cited By ~ 8

Author(s):

Macario Osorio-Concepción ◽

Gema Rosa Cristóbal-Mondragón ◽

Braulio Gutiérrez-Medina ◽

Sergio Casas-Flores

Keyword(s):

Oxidative Stress ◽

Histone Deacetylase ◽

Blue Light ◽

Stress Responses ◽

Wild Type ◽

Content Type ◽

Encoding Gene ◽

Oxidative Stress Responses ◽

And Oxidative Stress

ABSTRACT Fungal blue-light photoreceptors have been proposed as integrators of light and oxidative stress. However, additional elements participating in the integrative pathway remain to be identified. In Trichoderma atroviride, the blue-light regulator (BLR) proteins BLR-1 and -2 are known to regulate gene transcription, mycelial growth, and asexual development upon illumination, and recent global transcriptional analysis revealed that the histone deacetylase-encoding gene hda-2 is induced by light. Here, by assessing responses to stimuli in wild-type and Δhda-2 backgrounds, we evaluate the role of HDA-2 in the regulation of genes responsive to light and oxidative stress. Δhda-2 strains present reduced growth, misregulation of the con-1 gene, and absence of conidia in response to light and mechanical injury. We found that the expression of hda-2 is BLR-1 dependent and HDA-2 in turn is essential for the transcription of early and late light-responsive genes that include blr-1, indicating a regulatory feedback loop. When subjected to reactive oxygen species (ROS), Δhda-2 mutants display high sensitivity whereas Δblr strains exhibit the opposite phenotype. Consistently, in the presence of ROS, ROS-related genes show high transcription levels in wild-type and Δblr strains but misregulation in Δhda-2 mutants. Finally, chromatin immunoprecipitations of histone H3 acetylated at Lys9/Lys14 on cat-3 and gst-1 promoters display low accumulation of H3K9K14ac in Δblr and Δhda-2 strains, suggesting indirect regulation of ROS-related genes by HDA-2. Our results point to a mutual dependence between HDA-2 and BLR proteins and reveal the role of these proteins in an intricate gene regulation landscape in response to blue light and ROS. IMPORTANCE Trichoderma atroviride is a free-living fungus commonly found in soil or colonizing plant roots and is widely used as an agent in biocontrol as it parasitizes other fungi, stimulates plant growth, and induces the plant defense system. To survive in various environments, fungi constantly sense and respond to potentially threatening external factors, such as light. In particular, UV light can damage biomolecules by producing free-radical reactions, in most cases involving reactive oxygen species (ROS). In T. atroviride, conidiation is essential for its survival, which is induced by light and mechanical injury. Notably, conidia are typically used as the inoculum in the field during biocontrol. Therefore, understanding the linkages between responses to light and exposure to ROS in T. atroviride is of major basic and practical relevance. Here, the histone deacetylase-encoding gene hda-2 is induced by light and ROS, and its product regulates growth, conidiation, blue light perception, and oxidative stress responses.

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Listeria monocytogenes σB Has a Small Core Regulon and a Conserved Role in Virulence but Makes Differential Contributions to Stress Tolerance across a Diverse Collection of Strains

Applied and Environmental Microbiology ◽

10.1128/aem.00031-10 ◽

2010 ◽

Vol 76 (13) ◽

pp. 4216-4232 ◽

Cited By ~ 65

Author(s):

H. F. Oliver ◽

R. H. Orsi ◽

M. Wiedmann ◽

K. J. Boor

Keyword(s):

Oxidative Stress ◽

Listeria Monocytogenes ◽

Stress Response ◽

Cell Invasion ◽

Stress Responses ◽

Stress Conditions ◽

Infection Model ◽

Expression Microarrays ◽

Phylogenetic Lineages ◽

And Oxidative Stress

ABSTRACT Listeria monocytogenes strains are classified in at least three distinct phylogenetic lineages. There are correlations between lineage classification and source of bacterial isolation; e.g., human clinical and food isolates usually are classified in either lineage I or II. However, human clinical isolates are overrepresented in lineage I, while food isolates are overrepresented in lineage II. σB, a transcriptional regulator previously demonstrated to contribute to environmental stress responses and virulence in L. monocytogenes lineage II strains, was hypothesized to provide differential abilities for L. monocytogenes survival in various niches (e.g., food and human clinical niches). To determine if the contributions of σB to stress response and virulence differ across diverse L. monocytogenes strains, ΔsigB mutations were created in strains belonging to lineages I, II, IIIA, and IIIB. Paired parent and ΔsigB mutant strains were tested for survival under acid and oxidative stress conditions, Caco-2 cell invasion efficiency, and virulence using the guinea pig listeriosis infection model. Parent and ΔsigB mutant strain transcriptomes were compared using whole-genome expression microarrays. σB contributed to virulence in each strain. However, while σB contributed significantly to survival under acid and oxidative stress conditions and Caco-2 cell invasion in lineage I, II, and IIIB strains, the contributions of σB were not significant for these phenotypes in the lineage IIIA strain. A core set of 63 genes was positively regulated by σB in all four strains; different total numbers of genes were positively regulated by σB in the strains. Our results suggest that σB universally contributes to L. monocytogenes virulence but specific σB-regulated stress response phenotypes vary among strains.

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