Abstract
In the environment, bacteria show close association, such as interspecies interaction, with other bacteria as well as host organisms. The type VI secretion system (T6SS) in gram‐negative bacteria is involved in bacterial competition or virulence. The plant pathogen Burkholderia glumae BGR1, causing bacterial panicle blight in rice, has four T6SS gene clusters. The presence of at least one T6SS gene cluster in an organism indicates its distinct role, like in the bacterial and eukaryotic cell targeting system. In this study, deletion mutants targeting four tssD genes, which encode the main component of T6SS needle formation, were constructed to functionally dissect the four T6SSs in B. glumae BGR1. We found that both T6SS group_4 and group_5, belonging to the eukaryotic targeting system, act independently as bacterial virulence factors toward host plants. In contrast, T6SS group_1 is involved in bacterial competition by exerting antibacterial effects. The Δ tssD1 mutant lost the antibacterial effect of T6SS group_1. The ΔtssD1 mutant showed similar virulence as the wild‐type BGR1 in rice because the ΔtssD1 mutant, like the wild‐type BGR1, still has key virulence factors such as toxin production towards rice. However, metagenomic analysis showed different bacterial communities in rice infected with the ΔtssD1 mutant compared to wild‐type BGR1. In particular, the T6SS group_1 controls endophytic plant‐associated bacteria such as Luteibacter and Dyella in rice plants and may have an advantage in competing with endophytic plant‐associated bacteria for settlement inside rice plants in the environment. Thus, B. glumae BGR1 causes disease using T6SSs with functionally distinct roles.
Highlights
Myriad bacteria demonstrate close associations with nearby bacteria, as well as with their host organisms (Freestone, 2013; Stubbendieck et al, 2016)
2.7 | The endophytic bacterial community composition in noninfected rice, rice infected with B. glumae BGR1, and rice infected with ΔtssD1 differ because of the antibacterial activity of T6SS group_1
Endophytic bacterial communities in the noninfected rice, rice infected by BGR1, and rice infected by ΔtssD1 were separated clearly by a principal coordinate plot of distance based on the analysis of a weighted and unweighted UniFrac (p = .001, .006, respectively) (Figure 5c,d)
Summary
Myriad bacteria demonstrate close associations with nearby bacteria, as well as with their host organisms (Freestone, 2013; Stubbendieck et al, 2016). At 8 days post-inoculation (dpi) of the tested tssD mutants (ΔtssD1, ΔtssD2, ΔtssD4, ΔtssD5, ΔtssD12, ΔtssD45, and ΔtssD1245), only ΔtssD4, ΔtssD5, ΔtssD45, and ΔtssD1245 showed reduced virulence (Figure 2a) These results suggest that the T6SSs group_4 and group_5 were involved in bacterial virulence towards rice plants as the eukaryotic cell-targeting system. The complemented strain ΔtssD1-C, with recovered function of tssD1, showed antibacterial activity almost completely restored to wild-type levels, as reflected by a sharp decrease in the surviving number of E. coli prey cells (Figure 3b). 2.7 | The endophytic bacterial community composition in noninfected rice, rice infected with B. glumae BGR1, and rice infected with ΔtssD1 differ because of the antibacterial activity of T6SS group_1. The order Flavobacteriales in noninfected rice and the order Sphingobacteriales in rice infected by ΔtssD1 were abundant in the phylum Bacteroidetes, whereas at the phylum level, Proteobacteria were enriched in rice infected by BGR1
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.