ORIGINAL RESEARCH article
Front. Microbiol.
Sec. Infectious Agents and Disease
This article is part of the Research TopicPathogenic Gammaproteobacteria: Novel Insights into Virulence Mechanisms and Therapeutic InterventionView all 10 articles
The SPI-20 and SPI-21 T6SS gene clusters from Salmonella enterica subspecies arizonae encode effector proteins that display antibacterial activity
Provisionally accepted
Ayleen Parra-Calisto1
Carlos J Blondel2
Carla Vargas-del Río3Esteban Fernández-Castillo3
Felipe Reyes3Victoria Soriano-Mora3
Andrea Avilés4
Viviana Toledo3Fernanda Salazar-Salas5Patricio Espinoza-Jara3
Fernando A. Amaya4
Carlos A. Santiviago4
Juan A. Asenjo1
David Pezoa6*- 1Department of Chemical Engineering, Biotechnology and Materials, Centre for Biotechnology and Bioengineering (CeBiB), Universidad de Chile, Santiago, Chile
- 2Institute of Biomedical Sciences, Faculty of Medicine, Universidad Andres Bello, Santiago, Chile
- 3Núcleo de Investigación en One Health. Facultad de Medicina Veterinaria y Agronomía, Universidad de Las Américas, Campus Providencia, Manuel Montt 948, Santiago, Chile
- 4Laboratorio de Microbiología, Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Químicas y Farmacéuticas, Universidad de Chile, Santiago, Chile
- 5Escuela de Medicina, Facultad de Salud, Universidad del Alba, Santiago, Chile
- 6Universidad de Las Americas, Santiago, Chile
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ABSTRACT The type VI secretion system (T6SS) is a contact-dependent multiprotein apparatus that contributes to interbacterial competition and pathogenesis in many Gram-negative bacteria. Salmonella harbors five T6SS gene clusters within the pathogenicity islands SPI-6, SPI-19, SPI-20, SPI-21, and SPI-22, differentially distributed among serotypes. Salmonella enterica subspecies arizonae (S. arizonae) is most frequently associated with reptiles but, in some circumstances, can cause disease in mammals, including humans. Notably, although it encodes both the SPI-20 and SPI-21 T6SSs, no report to date has demonstrated the antibacterial activity of either system. In addition, only two putative effector proteins have been previously predicted, though they have not been experimentally validated. In the present study, we demonstrate that both T6SSSPI-20 and T6SSSPI-21 contribute to interbacterial competition when grown in McConkey agar plates in S. arizonae, suggesting a role for bile in SPI-20 and SPI-21 T6SS activity. In addition, through bioinformatic analyses, interbacterial competition assays, and heterologous expression, we further characterize the antibacterial activity of a novel antibacterial E/I module (SARI_02625/SARI_02624, encoded in SPI-21) that, in addition to the previously identified evolved VgrG protein SARI_02603 and VgrG2b homolog SARI_02727, contribute to T6SS-dependent antibacterial competition in S. arizonae.
Keywords: effector, immunity proteins, interbacterial competition, Salmonella arizonae, T6SS
Received: 18 Dec 2025; Accepted: 10 Feb 2026.
Copyright: © 2026 Parra-Calisto, Blondel, Vargas-del Río, Fernández-Castillo, Reyes, Soriano-Mora, Avilés, Toledo, Salazar-Salas, Espinoza-Jara, Amaya, Santiviago, Asenjo and Pezoa. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: David Pezoa
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