Abstract
Klebsiella spp. have been isolated from many different environmental habitats but have mainly been associated with nosocomial acquired diseases in humans. Although there are many recently published sequenced genomes of members of this genus, there are very few studies on whole genome comparisons between clinical and non-clinical isolates, and it is therefore still an open question if a strain found in nature is capable of infecting humans/animals. Klebsiella michiganensis Kd70 was isolated from the intestine of larvae of Diatraea saccharalis but genome analysis revealed multiple genes associated with colonization and growth promotion in plants suggesting an endophytic lifestyle. Kd70 cells labeled with gfp confirmed capability of root colonization and soil application of Kd70 promoted growth in greenhouse grown sugarcane. Further genomic analysis showed that the Kd70 genome harbored fewer mammalian virulence factors and no pathogen island-like regions when compared to clinical isolates of this species, suggesting attenuated animal/human pathogenicity. This postulation was corroborated by in vivo experiments in which it was demonstrated that Kd70 was unable to infect the mouse urinary tract. This is to the best of our knowledge the first experimental example of a member of a pathogenic Klebsiella spp. unable to infect a mammalian organism. A proteomic comparison deduced from the genomic sequence between Kd70 and several other K. michiganensis strains showed a high similarity with isolates from many different environments including clinical strains, and demonstrated the existence of conserved genetic lineages within this species harboring members from different ecological niches and geographical locations. Furthermore, most genetic differences were found to be associated with genomic islands of clinical isolates, suggesting that evolutionary adaptation of animal pathogenicity to a large extent has depended on horizontal gene transfer. In conclusion our results demonstrate the importance of conducting thorough in vivo pathogenicity studies before presupposing animal/human virulence of non-clinical bacterial isolates.
Highlights
Klebsiella is a genus of Gram-negative, rod-shaped, nonmotile, facultative anaerobe bacteria that normally produces a prominent polysaccharide capsule which provides resistance against host defense systems
The draft genome sequence of Kd70 was aligned against two previously sequenced clinical isolates of K. oxytoca/michiganensis, JKo3 one of its closest phylogenetic relatives and the genetically more distant E718, which were used as reference genomes
The genomic analysis of Kd70 strongly indicated that this bacteria is an endophytic strain with important plant growth promoting activity, originally being isolated from the intestine of a larva of D. saccharalis (Dantur et al, 2015)
Summary
Klebsiella is a genus of Gram-negative, rod-shaped, nonmotile, facultative anaerobe bacteria that normally produces a prominent polysaccharide capsule which provides resistance against host defense systems. Klebsiella spp. are able to produce high quantities of extracellular phytohormones like indoleacetic acid (IAA) and tryptophol and low levels of indolepyruvate and indoleacetaldehyde (ElKhawas and Adachi, 1999; Shokri and Emtiazi, 2010; Liu et al, 2013), to solubilize phosphate by expressing a significant level of acid phosphatases (Thaller et al, 1995; Ahemad and Kibret, 2014) and to produce catechol and hydroxamate types of siderophores (Podschun et al, 1992, 2001), traits that are strongly associated with plant growth promotion by providing the plant with nutrients, minerals, and hormones (Glick, 2012) Another important characteristic found for many PGPR strains including Klebsiella spp. is their capacity to form biofilm. The formation of biofilm is important for effective colonization on or in the plant root, helping the bacteria to compete well with indigenous microflora and at the same time generating improved plant growth promotion by improved N2-fixation, mineral uptake, phosphorus solubilization or abiotic and pathogen protection (Seneviratne et al, 2011)
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