Evidence for remarkable genetic plasticity of bacterial linear plasmids from extreme environments

DIB, JULIÁN RAFAEL; WAGENKNECHT, MARTIN; THÜRNER, ANDREA; SCHULDES, JÖRG; FARÍAS, MARIA EUGENIA; DANIEL, ROLF; MEINHARDT, FRIEDHELM

Ljubljana

Congreso; 12th Symposium on Bacterial Genetics and Ecology (BAGECO); 2013

BAGECO

Members of the spore-less actinomycetous genus Micrococcus have a great potential for biodegradation and are, thus, of ecological importance for bioremediation. Moreover, they constitute a frequent source of biotechnologically relevant enzymes and bioactive compounds. Micrococcus bacteria withstand diverse harsh environmental conditions: they are able to survive in millions of years old amber samples, in carefully decontaminated space stations, and in oligotrophic, extremely saline and heavy-metal containing lakes of the high-altitude Argentinean Puna. Several strains isolated from the latter carry large, linear, extrachromosomal genetic elements with proteins covalently attached to their 5´ ends (termed linear plasmids). For a broader inspection of the potential of the linear plasmids for the survival and/or adaptation to such harsh environment, two different linear plasmids (pLMA1 and pLMA7, with sizes of 110 kb and 82 kb, respectively) were analysed in detail. The plasmids were electro-eluted from PFGE gels and subsequently checked for blocked ends by exonuclease III and λ-exonuclease treatments. Sequencing was performed applying the Sanger technology in combination with 454 pyrosequencing. Remaining gaps were closed manually by PCR. Obtained sequences were analyzed using standard bioinformatics tools. The elements were seen to share a rather conserved common backbone, consisting of 11 identically arranged sequence blocks comprising approximately 51 kb (G+C content 70.5 %), which are mainly composed of genes encoding essential plasmid functions and conjugal DNA-transfer. The plasmids differ in their respective accessory regions (G+C content on the average 66-67%), which consist of numerous mobile genetic elements potentially providing the basis for resistance to stress conditions and genetic plasticity. The capability for conjugal transfer (facilitated by the common backbone) along with the multitude of transposable elements (present as accessory DNA) identifies the Micrococcus linear plasmids as extremely flexible, mobile, rather plastic genetic elements with the potential to enable the host bacteria to conquer and adapt to extreme ecological niches.