Functional characterization of MarR family transcription factors in Chromobacterium violaceum

Author(s)

Maristela Previato Mello

• Document type: Doctoral Thesis
• Press: Ribeirão Preto.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina de Ribeirão Preto (PCARP/BC)
• Defense date: 2018-06-13

Examining board members

José Freire da Silva Neto; Cristina Elisa Alvarez Martinez; Cristiano Gallina Moreira; Nilce Maria Martinez Rossi; Dario Simões Zamboni

• Advisor: José Freire da Silva Neto

Abstract

Transcription factors belonging to the MarR family act as direct intracellular sensors of signals and control many processes in bacteria, including virulence and degradation of aromatic compounds. In this work, we identify and characterize MarR family transcription factors controlling virulence in Chromobacterium violaceum, an opportunistic pathogen of humans. Using allelic exchange mutagenesis, we generate non-polar null mutants for twelve of the fifteen MarR family regulators found in the C. violaceum genome. In virulence tests, when introduced by intraperitoneal injection in BALB/c mice, the ?CV_0210 (?ohrR), ?CV_0577 and ?CV_2726 mutant strains were less virulent, while the ?CV_1776 was more virulent, when compared to the wild-type strain. The other nine MarR mutants showed no difference in virulence tests. To define the regulon of some MarR family transcription factors, the gene expression profiles were determined by DNA microarray analysis and Northern blot assays for the ?CV_0210 (?ohrR), ?CV_1776, ?CV_1810 and ?CV_2726 mutant strains, for the wild-type strain overexpressing CV_2726 and for the wild-type strain exposed to oxidative stress generated by cumene hydroperoxide (CHP). The CV_1810 is a repressor of a regulon that comprised two divergent operons encoding enzymes that possibly metabolize aromatic compounds, but catabolic products of these compounds did not function as ligands capable of antagonizing the repression of CV_1810 on the CV_1801 gene. The regulon of the activator CV_2726, defined as fourteen differentially expressed genes commonly found in assays in the absence and overexpression of the CV_2726 gene, revealed few genes (cstA) with potential to be involved in the phenotype of lower virulence of the ?CV_2726 mutant strain. Regulators CV_0577 and CV_1776 were allocated in the urate-responsive UrtR subfamily and probably afect the virulence of C. violaceum with overlapping regulons. The CV_1776 regulon contains dozens of genes, many of them related to amino acid catabolism, but there are few candidates for classical virulence factors (pecM, escU). Some genes related to catabolism/utilization of purine (CV_0578 and CV_3771) were 12 regulated by both CV_1776 and CV_0577 and responded to the presence of urate. The transcriptional profile of the adaptive response of C. violaceum to CHP, a ligand that oxidizes the OhrR regulator, revealed the upregulation of genes related to the detoxification of peroxides (antioxidant enzymes and thiol-reducing systems), degradation of the aromatic moiety of CHP (oxygenases), and protection against other secondary stresses (DNA repair, heat shock, iron limitation, and nitrogen starvation responses). The OhrR regulon was shown to be small, including two upregulated genes, CV_0209 (ohrA) and CV_0208 (putative diguanylate cyclase), and three downregulated genes (hemolysin, chitinase, and collagenase) in the ?ohrR mutant. Thus, the attenuated virulence of the ?ohrR mutant might be related to the increased production of the second messenger cyclic di-GMP (c-di-GMP) and the decreased expression of extracellular enzymes required for tissue dissemination, in this mutant strain. In conclusion, we have defined the transcriptional response to CHP, identified potential virulence factors such as diguanylate cyclase as members of the OhrR regulon, and shown that C. violaceum uses the transcription factors of the MarR family CV_0577, CV_1776, CV_2726 and OhrR to modulate its virulence. (AU)

• FAPESP's process: 13/25745-9 - Functional characterization of MarR family transcription factors in Chromobacterium violaceum
• Grantee: Maristela Previato Mello
• Support Opportunities: Scholarships in Brazil - Doctorate