Abstract
Type II toxin-antitoxin (TA) systems are genetic elements usually encoding two proteins: a stable toxin and an antitoxin, which binds the toxin and neutralizes its toxic effect. The disturbance in the intracellular toxin and antitoxin ratio typically leads to inhibition of bacterial growth or bacterial cell death. Despite the fact that TA modules are widespread in bacteria and archaea, the biological role of these systems is ambiguous. Nevertheless, a number of studies suggests that the TA modules are engaged in such important processes as biofilm formation, stress response or virulence and maintenance of mobile genetic elements. The Dickeya dadantii 3937 strain serves as a model for pathogens causing the soft-rot disease in a wide range of angiosperm plants. Until now, several chromosome-encoded type II TA systems were identified in silico in the genome of this economically important bacterium, however so far only one of them was experimentally validated. In this study, we investigated three putative type II TA systems in D. dadantii 3937: ccdAB2Dda, phd-docDda and dhiTA, which represents a novel toxin/antitoxin superfamily. We provide an experimental proof for their functionality in vivo both in D. dadantii and Escherichia coli. Finally, we examined the prevalence of those systems across the Pectobacteriaceae family by a phylogenetic analysis.
Highlights
Soft-rot Pectobacteriaceae (SRP) are Gram-negative, non-spore forming facultative anaerobic bacteria causing soft-rot disease in a wide range of angiosperm plants, limiting the crop yield and quality
Despite the fact that the biological role of TA systems remains elusive in general, a number of data implies that some of them could be essential for virulence, biofilm formation and motility in bacterial plant pathogens [19,20,22,23]
The putative type II chromosome-encoded TA systems of D. dadantii 3937 selected for investigation in this study were chosen from among TA modules previously predicted in silico and deposited in the NCBI database (D. dadantii 3937 NC_014500.1 [9]) or, in the case of DDA3937_RS07415/RS07420 system, predicted by a DNA sequence search with TAfinder [26] and RASTABacteria [27]
Summary
Soft-rot Pectobacteriaceae (SRP) are Gram-negative, non-spore forming facultative anaerobic bacteria causing soft-rot disease in a wide range of angiosperm plants, limiting the crop yield and quality. It was suggested that climate change is likely to accelerate evolution and to increase the diversity of bacterial plant pathogens [1,7,8] This makes SRP one of the most scientifically and economically significant group of phytopathogenic bacteria. Since the genome sequence of D. dadantii 3937 was published in 2011 [9], it provided an opportunity to identify and examine chromosome-encoded toxin-antitoxin (TA) systems in this model bacterium. This opportunity is especially fascinating since relatively little is known about those elements in bacterial plant pathogens [10]. We supply experimental proof for the existence of a novel type II TA system in the model bacterium D. dadantii 3937
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