AUTHOR=Shyntum Divine Yufetar , Nkomo Ntombikayise Precious , Shingange Ntwanano Luann , Gricia Alessandro Rino , Bellieny-Rabelo Daniel , Moleleki Lucy Novungayo 

TITLE=The Impact of Type VI Secretion System, Bacteriocins and Antibiotics on Bacterial Competition of Pectobacterium carotovorum subsp. brasiliense and the Regulation of Carbapenem Biosynthesis by Iron and the Ferric-Uptake Regulator

JOURNAL=Frontiers in Microbiology

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2019.02379

DOI=10.3389/fmicb.2019.02379

ISSN=1664-302X

ABSTRACT=<p>The complexity of plant microbial communities provides a rich model for investigating biochemical and regulatory strategies involved in interbacterial competition. Within these niches, the soft rot <italic>Enterobacteriaceae</italic> (SRE) represents an emerging group of plant–pathogens causing soft rot/blackleg diseases resulting in economic losses worldwide in a variety of crops. A preliminary screening using next-generation sequencing of 16S rRNA comparatively analyzing healthy and diseased potato tubers, identified several taxa from <italic>Proteobacteria</italic> to <italic>Firmicutes</italic> as potential potato endophytes/plant pathogens. Subsequent to this, a range of molecular and computational techniques were used to determine the contribution of antimicrobial factors such as bacteriocins, carbapenem and type VI secretion system (T6SS), found in an aggressive SRE (<italic>Pectobacterium carotovorum</italic> subsp. <italic>brasiliense</italic> strain PBR1692 – <italic>Pcb</italic>1692) against these endophytes/plant pathogens. The results showed growth inhibition of several <italic>Proteobacteria</italic> by <italic>Pcb</italic>1692 depends either on carbapenem or pyocin production. Whereas for targeted <italic>Firmicutes</italic>, only the <italic>Pcb</italic>1692 pyocin seems to play a role in growth inhibition. Furthermore, production of carbapenem by <italic>Pcb</italic>1692 was observably dependent on the presence of environmental iron and oxygen. Additionally, upon deletion of <italic>fur</italic>, <italic>sly</italic>A and <italic>exp</italic>I regulators, carbapenem production ceased, implying a complex regulatory mechanism involving these three genes. Finally, the results demonstrated that although T6SS confers no relevant advantage during <italic>in vitro</italic> competition, a significant attenuation in competition by the mutant strain lacking a functional T6SS was observed <italic>in planta</italic>.</p><sec><title>IMPORTANCE</title><p>Soft rot <italic>Enterobacteriaceae</italic> (SRE) represents important phytopathogens causing soft rot/blackleg diseases in a variety of crops leading to huge economic losses worldwide. These pathogens have been isolated alongside other bacteria from different environments such as potato tubers, stems, roots and from the soil. In these environments, SREs coexist with other bacteria where they have to compete for scarce nutrients and other resources. In this report, we show that <italic>Pectobacterium carotovorum</italic> subsp. <italic>brasiliense</italic> strain PBR1692 – <italic>Pcb</italic>1692, which represents one of the SREs, inhibits growth of several different bacteria by producing different antimicrobial compounds. These antimicrobial compounds can be secreted inside or outside the plant host, allowing <italic>Pcb</italic>1692 to effectively colonize different types of ecological niches. By analyzing the genome sequences of several SREs, we show that other SREs likely deploy similar antimicrobials to target other bacteria.</p></sec>