Thiosulfinate tolerance gene clusters are common features ofBurkholderiaonion pathogens

Abstract

AbstractBurkholderia gladiolipv.alliicola, B.cepacia, andB. orbicolaare common bacterial pathogens of onion. Onions produce organosulfur thiosulfinate defensive compounds after cellular decompartmentalization. Using whole genome sequencing andin silicoanalysis, we identified putative thiosulfinate tolerance gene (TTG) clusters in multiple onion-associatedBurkholderiaspecies similar to those characterized in otherAllium-associated bacterial endophytes and pathogens. Sequence analysis revealed the presence of threeBurkholderiaTTG cluster types with both Type A and Type B being broadly distributed inB. gladioli,B. cepacia, andB. orbicolain both the chromosome and plasmids. Based on isolate natural variation and generation of isogenic strains, we determined thein vitroandin vivocontribution of TTG clusters inB. gladioli,B. cepacia, andB. orbicola. TheBurkholderiaTTG clusters contributed to enhanced allicin tolerance and improved growth in filtered onion extract by all three species. TTG clusters also made clear contributions toB gladiolifoliar necrosis symptoms and bacterial populations. Surprisingly, the TTG cluster did not contribute to bacterial populations in onion bulb scales by these three species. Based on our findings, we hypothesize onion-associatedBurkholderiamay evade or inhibit the production of thiosulfinates in onion bulb tissues.