General Notices

The Department of Life Sciences invites the campus community to the PhD Oral Examination for Mr. Stephen Ramnarine, PhD inMicrobiology candidate on Wednesday, March 20 at 10a.m. Mr Ramnarine will address the topic Molecular Characterization of Copper Resistance and Virulence Features of Xanthomonas campestris pv. campestris Strains Indigenous to Trinidad, W.I.

Interested persons can join in-person at the FST Dean's Office Board room or via Zoom by clicking here.

ABSTRACT:

This study explores the all-too-common phenomenon of copper resistance in phytopathogens that pose a great challenge to crop disease management globally. Specifically focusing on the crucifer infecting blackrot pathogen, Xanthomonas campestris pv. campestris (Xcc), the work presented in this thesis seeks to update and broaden the understanding of copper resistance in Xcc strains. Xanthomonas spp. were isolated from active cabbage and cauliflower fields with persistent black rot infections between 2015-2017. The prevalence of copper resistance and tolerance in local strains were much higher when compared to a previous study done between 1999-2001. Molecular analysis of the copper resistance copLAB genes revealed the occurrence of 3 distinct clades including one unique cluster characterised in a previous study. In the 2015-2017 isolate collection, this unique cluster was only found in Xcc from Aranguez where the original Xcc strain was isolated in 1999. For the first time, comparative genomic analysis of local Xcc strains, contributed draft genomes to global databases and elucidated unique genomic features. Most importantly, a heterogenous Type III secretion system and two plasmid-borne heavy metal resistance cop containing gene clusters were documented. Homologs to these heavy metal gene clusters were identified in global Stenotrophomonas chromosomes, however, no local strain from this genus contained these genes. The molecular cascade of Xcc to copper ion shock was characterised using hybrid transcriptome profiling, which allowed for a greater understanding and pathway modelling of this response in Xcc. MDR efflux pumps and a heavy metal resistance gene cluster were identified for further evaluation under different levels of copper stress, other heavy metals, and antibiotics. Multi-resistance to many heavy metals and antibiotics were characterised and the expression profiles of the entire heavy metal resistance island after copper ion induction was noted. Furthermore, 4 MDR efflux pump targets putatively involved in the initial response to copper and other heavy metal stress in Xcc were identified. This study establishes the importance of evaluating multiple resistance patterns in phytopathogens and provides much-needed reference draft genomes of Xcc from Trinidad. The use of targeted expression studies also highlights conserved homologous elements in the complex response of Xcc and other Xanthomonads to copper and heavy metal stress. 

Keywords: Copper Resistant Bacteria; Xanthomonas campestris pv. campestris; copLAB; Heavy Metal Resistance, Xanthomonas Resistome