Abstract
Pectobacterium carotovorum subsp. carotovorum (Pcc) causes soft-rot disease in a wide variety of plants resulting in economic losses worldwide. It produces various types of bacteriocin to compete against related plant pathogens. Studies on how bacteriocins are extracellularly secreted are conducted to understand the mechanism of interbacterial competition. In this study, the secretion of the low-molecular-weight bacteriocins (LMWB) Carocin S1 and Carocin S3 produced by a multiple-bacteriocin producing strain of Pcc, 89-H-4, was investigated. Tn5 insertional mutagenesis was used to generate a mutant, TH22–6, incapable of LMWBs secretion. Sequence and homology analyses of the gene disrupted by transposon Tn5 insertion revealed that the gene sctT, an essential component of the injectisome type III secretion machinery (T3aSS), is required for the secretion of the bacteriocins. This result raised a question regarding the nature of the secretion mechanism of Pcc bacteriocins which was previously discovered to be secreted via T3bSS, a system that utilizes the bacterial flagellum for extracellular secretions. Our previous report has shown that bacteriocin Carocin S1 cannot be secreted by mutants that are defective of T3bSS-related genes such as flhA, flhC, flhD and fliC. We knocked out several genes making up the significant structural components of both T3aSS and T3bSS. The findings led us to hypothesize the potential roles of the T3aSS-related proteins, SctT, SctU and SctV, as flagellar T3SS chaperones in the secretion of Pcc bacteriocins. This current discovery and the findings of our previous study helped us to conceptualize a unique Type III secretion system for bacteriocin extracellular export which is a hybrid of the injectisome and flagellar secretion systems.
Highlights
Many bacteria often produce extracellular proteins to inhibit the growth of other competing bacterial species [1, 2]
We chose H-rif-8-6, which was from the rifampicin resistant strain 89-H-4, as the recipient of bacterial conjugation, and E. coli (1830) with the kanamycin resistance gene transposon Tn5 as the donor of conjugative reproduction
The results have shown that deletion of sctU, sctV, flgG, fliE and fliR genes disabled the Results from our previous research have shown the significance of flhA, flhC, flhD, and fliC genes in regulating the synthesis of bacterial flagella in Pectobacterium carotovorum subsp. carotovorum (Pcc) and that Carocin S1 utilizes this secretion machinery (T3bSS) [20]
Summary
Many bacteria often produce extracellular proteins to inhibit the growth of other competing bacterial species [1, 2]. Such extracellular proteins produced are commonly called bacteriocins. Carotovorum (Pcc), the genes responsible for bacteriocins production is in the chromosomes [7,8,9,10]. When the bacterial growth environment changes and may cause harm, the structural genes in the chromosome will be activated to produce bacteriocin proteins to attack other related bacterial species. Because bacteriocin has the function of inhibiting the growth of other competing species, we can often see in some related literature that the bacteriocin protein produced by the isolated harmless bacterial species is transferred to other bacteria. Bacteriocins usually inhibit the growth of closely related harmful bacteria [11], which shows that some bacteriocins might have a high application value and economic significance
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
