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The euryarchaeon Thermococcus kodakarensis is a well-characterized anaerobic hyperthermophilic heterotroph and due to the availability of genetic engineering systems it has become one of the model organisms for studying Archaea. Despite this prominent role among the Euryarchaeota, no data about the ploidy level of this species is available. While polyploidy has been shown to exist in various Euryarchaeota, especially Halobacteria, the chromosome copy number of species belonging to one of the major orders within that phylum, i.e., the Thermococcales (including Thermococcus spp. and Pyrococcus spp.), has never been determined. This prompted us to investigate the chromosome copy number of T. kodakarensis. In this study, we demonstrate that T. kodakarensis is polyploid with a chromosome copy number that varies between 7 and 19 copies, depending on the growth phase. An apparent correlation between the presence of histones and polyploidy in Archaea is observed. Electronic supplementary material The online version of this article (doi:10.1007/s00792-015-0750-5) contains supplementary material, which is available to authorized users.

High-level, recombinant production of membrane-integrated proteins in Escherichia coli is extremely relevant for many purposes, but has also been proven challenging. Here we study a combination of transcriptional fine-tuning in E. coli LEMO21(DE3) with different codon usage algorithms for heterologous production of membrane proteins. The overex- pression of 6 different membrane proteins is compared for the wild-type gene codon usage variant, a commercially codon-optimized variant, and a codon-harmonized variant. We show that transcriptional fine-tuning plays a major role in improving the production of all tested proteins. Moreover, different codon usage variants significantly improved production of some of the tested proteins. However, not a single algorithm performed consistently best for the membrane-integrated production of the 6 tested proteins. In conclusion, for improving heterologous membrane protein production in E. coli, the major effect is accomplished by transcriptional tuning. In addition, further improvements may be realized by attempting dif- ferent codon usage variants, such as codon harmonized variants, which can now be easily generated through our online Codon Harmonizer tool.