Type VI secretion system of Chromobacterium violaceum: study of regulation and effectors targeting the cell wall

• Grant number: 25/10981-6
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• Start date: August 01, 2025
• End date: November 30, 2026
• Field of knowledge: Biological Sciences - Genetics - Molecular Genetics and Genetics of Microorganisms
• Principal Investigator: José Freire da Silva Neto
• Grantee: Mateus de Souza Terceti
• Host Institution: Faculdade de Medicina de Ribeirão Preto (FMRP). Universidade de São Paulo (USP). Ribeirão Preto , SP, Brazil
• Associated research grant: 21/06894-0 - Bacterial transcription factors involved in metal homeostasis, oxidative stress and virulence: investigating how Chromobacterium violaceum switches from the environment to the host, AP.JP2

Abstract

The Type VI Secretion System (T6SS) is a contractile machinery present in Gram-negative bacteria that enables the translocation of effector proteins, most of which are antibacterial, into target cells. It plays a crucial role in bacterial competition and pathogenicity, as well as in the acquisition of scarce metals from the environment. Our group has been studying the T6SS of Chromobacterium violaceum, an environmental Gram-negative bacterium capable of causing opportunistic infections in humans. We have demonstrated that the T6SS of C. violaceum is regulated by quorum sensing and that its primary function is competition against other bacteria. However, most of the antibacterial effectors of this T6SS have not yet been characterized, and the pathways regulating its expression and activity in a cell density-dependent manner are still unknown. Additionally, it has not yet been tested whether the T6SS of C. violaceum is involved in the uptake of metal ions. In this project, we propose to study these unknown aspects of the T6SS of C. violaceum through: i) Screening a transposon library to identify mutants with altered T6SS activity patterns, aiming to discover new regulatory pathways; ii) Evaluating the expression of T6SS components under iron-limited conditions and in the fur mutant; iii) Mutagenesis, expression, and purification of three potential effectors with possible action on the cell wall, CV_0024, CV_2125, and CV_2665, to assess their toxicity in heterologous expression contexts and interbacterial competition. The results of this project are expected to contribute to the identification of new regulatory mechanisms and to the characterization of novel effectors of this still relatively understudied T6SS.