Submitted to: Current Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/3/2017
Publication Date: 7/31/2017
Citation: Medrano, E.G., Bell, A.A. 2017. Demonstration that a Klebsiella pneumoniae subsp. pneumoniae isolated from an insect (Nezara viridula) harbors a functional plasmid-borne type IV secretion system. Current Microbiology. 74:1033–1042.
Interpretive Summary: In studying pathogens of cotton bolls and their respective piercing-sucking insect vectors, we recovered a bacterium and classified it as Klebsiella pneumoniae. The bacterial strain called Kp 5-1 is capable of rotting cotton bolls and was originally isolated from a southern green stink bug (Nezara viridula) that is a significant pest of cotton. Interestingly, K. pneumoniae is a known human pathogen that causes bacterial pneumonia; it is not an apparent pathogen of the stink bug. Previously, we sequenced the whole genome of the cotton pathogen Kp 5-1 in an attempt to identify genes with products that are involved in cotton pathogenicity. Here, we report the identification of a bacterial secretion system and demonstrated its functionality. The secretion apparatus is classified as a type IV secretion system (from six known systems) that is composed of a set of over 20 genes and is known to be involved in the movement of DNA from one bacterium to another and for delivery of toxins into infected hosts. Results from this paper showed that the identified microbial apparatus can readily transfer DNA between bacteria. We hypothesize that if virulence genes are amongst the shared DNA, then previously non-pathogenic bacteria could be converted into pathogens. This work is an important step towards gaining basic knowledge of bacterial plant pathogenicity using a cotton pathogen as a model system.
Technical Abstract: Previously, we reported the isolation of Klebsiella pneumoniae subspecies pneumoniae strain Kp 5-1 from a southern green stink bug (Nezara viridula) that is a significant pest of numerous economically important crops. We subsequently sequenced the strains whole genome. Here, we report the presence of a functional plasmid-borne type IV secretion (TFSS) system that was identified using genomic mining of the annotated genome. Comparison of the Kp 5-1 resident 186 kb plasmid (pKp 5-1) with nine other Klebsiella with plasmids of comparable size from clinical and environmental strains revealed putative TFSS with identities ranging from 70 – 99%. A primer set was designed at the pKp 5-1 region that shared homology with traC of the conjugation capable F-plasmid. The 2.4 kb amplified PCR product was cloned, sequenced, and used in hybridization experiments verify that the predicted gene was extra-chromosomally located. Based on biparental mating experimental results, a K. pneumoniae Kp 5-1 derivative transformed with the non-self-transmissible pMMB207alpha beta (an IncQ RSF1010 derivative) mobilized the vector into the parental strain with transfer frequencies of 10-3 transconjugants/donor. Identification of a TFSS in strain Kp 5-1 is significant since in other systems the mobilization capacity is involved in dissemination of plasmids that may confer antibiotic resistance and/or the delivery of virulence proteins into host cells, and thus may have an important role in the fitness of this strain as well. This is the first report that both compared and demonstrated functionality of a plasmid harbored TFSS in a K. pneumoniae isolated from a N. viridula.