Exploring the (Almost) Unknown: Archaeal Two-Component Systems

ABSTRACT Two-component systems (TCS) exist in bacteria and archaea. In contrast to the knowledge of bacterial TCSs, little information is available on their archaeal counterparts. In the current issue of Journal of Bacteriology , Galperin and coworkers present a bioinformatics analysis of TCS genes from archaeal genome sequences (M. Y. Galperin, K. S. Makarova, Y. I. Wolf, and E. V. Koonin, J Bacteriol 200:e00681-17, 2018, https://doi.org/10.1128/JB.00681-17 ). This study identifies different aspects in which TCS-mediated signaling differs in bacteria and archaea and forms a sound basis for the experimental design of studies to increase our knowledge of this poorly investigated protein family.

How big is the iceberg of which organellar genes in nuclear genomes are but the tip?

As more and more complete bacterial and archaeal genome sequences become available, the role of lateral gene transfer (LGT) in shaping them becomes more and more clear. Over the long term, it may be the dominant force, affecting most genes in most prokaryotes. We review the history of LGT, suggesting reasons why its prevalence and impact were so long dismissed. We discuss various methods purporting to measure the extent of LGT, and evidence for and against the notion that there is a core of never–exchanged genes shared by all genomes, from which we can deduce the ‘true’ organismal tree. We also consider evidence for, and implications of, LGT between prokaryotes and phagocytic eukaryotes.