Title : Conversion of a defensive toxin-antitoxin system into an offensive T6SS effector in Burkholderia.
Speaker : Dr Gopaljee Jha, Staff Scientist V, Plant-Microbe Interactions Lab, NIPGR, New Delhi.
Date : 09/11/2021, 06:00 PM (Monday), Online Mode.
We have previously identified Burkholderia gladioli strain NGJ1 from rice, which exhibits a novel ability to feed on fungi, a phenomenon known as mycophagy. We have demonstrated that functional type III secretion system (T3SS) is required for microphagous ability of NGJ1. Further, we have reported that NGJ1 deploys a prophage tail-like protein (Bg_9562) into fungal cells in a T3SS dependent manner to feed on fungi. Our recent study has revealed that beside mycophagy, NGJ1 also exhibits broad-spectrum antibacterial activity and type VI secretion system (T6SS) is required for contact-dependent killing of the prey bacteria. Generally, bacteria utilize various kinds of toxins to either inhibit the growth of co-habiting bacteria or when needed control their own growth. We report that Burkholderia and certain other bacteria have altered the potential defensive function of Tox-REase-5 domain containing toxins into offensive function. The NGJ1 encodes such toxins as T6SS effectors (TseTBg) and potentially deploys them to kill co-habiting rice endophytic bacteria. Notably, the immunity (TsiTBg) proteins associated with TseTBg effectors demonstrate functional similarity with the antitoxin of type II toxin-antitoxin (TA) system. Genome analysis of diverse bacteria revealed that various TseTBg orthologs are either encoded as TA or T6SS effectors. In addition, potential evolutionary events associated with conversion of TA into T6SS effectors have been delineated. Our results indicate that the transposition of IS3 elements has led to the operonic fusion of certain T6SS related genes with TA genes resulting in their conversion into T6SS effectors. Such a genetic change has enabled bacteria to utilize novel toxins to precisely target co-habiting bacteria.
Gopaljee Jha obtained his M.Sc in Biotechnology from Guru Nanak Dev University, India. He has completed his PhD (in 2008) from CSIR-CCMB, Hyderabad, under the supervision of Dr Ramesh Sonti. Then, he joined as a scientist at CSIR-Institute of Himalayan Bioresource Technology, Palampur, H.P, India. He carried out his postdoctoral research at Sainsbury Laboratory, John Innes Centre, Norwich, U.K. He is currently working as Staff Scientist V in the Plant-Microbe Interactions unit of the National Institute of Plant Genome Research, New Delhi. His group carries integrated research with the main focus on understanding how pathogens cause disease and plants defend themselves. He is a recipient of the INSA medal for Young Scientist (2010), NASI Platinum Jubilee Young Scientist Award (2007), BOYSCAST Fellowship from the Department of Science and Technology (2010-2011) and DST-Swarna Jayanti Fellowship 2020.