Authors:

Palash Ghosh

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About Paper:

Type VI secretion system (T6SS) is a complex nanomolecular machine in gram-negative bacteria and majorly in present in Proteobacteria, that injects toxins or effectors into neighboring targets prokaryotic or eukaryotic cells. Performing like a crossbow, T6SS plays a crucial role in interbacterial competition, host colonization and niche adaptation. Xanthomonas perforans causes bacterial leaf spot disease on tomato (Solanum lycopersicum) and pepper (Capsicum annuum) that severely impacts crops globally. X. perforans strain AL65 have two clusters of T6SS (named as i3* and i3***) however, our understanding of T6SS in this pathosystem and its role in microbiome associated inter-bacterial competition, host and niche adaption is limited. To address these questions, we conducted a screening using a promoter-activated GFP plasmid (pPROBE) tagged with X. perforans AL65 to learn whether we observe activation of T6SS against diverse tomato phyllosphere microbiota bacterial members and against conditions such as pH, salinity, antibiotics etc. Our results identified certain phyllosphere residents whose interaction with X. perforans AL65 led to activation of T6SS clusters. We also evaluated T6SS activation in response to various environmental stresses and antibiotics. We also observed a constant activation of T6SS without any external stimuli whether it is biotic or abiotic stress. Our findings highlight how the T6SS of X. perforans AL65 remain vigilant and defensive to overcome any stresses such as tomato phyllosphere isolates and also helps the pathogen's survival under diverse environmental conditions during epiphytic colonization which may provide competitive advantage in disease progression.

Source:

Auburn University / College of Agriculture / 2025

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Co-authors:

Palash Ghosh