Journal of Basic Microbiology 2010, 50, 227 – 231 227 © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.jbm-journal.com Research Paper Expression of hcp in freshwater Synechococcus spp., a gene encoding a hyperconserved protein in picocyanobacteria Olga A. Kutovaya, R. Michael L. McKay and George S. Bullerjahn Department of Biological Sciences, Bowling Green State University, Life Sciences Building, Bowling Green, USA Marine picoplankton of the genus Synechococcus and Prochlorococcus spp. are widely studied members of the picocyanobacterial clade, composed of unicellular cyanobacteria that dominate pelagic regions of the ocean. Less studied are the related freshwater Synechococcus spp. that similarly dominate the euphotic zone of oligotrophic lakes. Previous work has shown that marine picocyanobacteria harbor a small gene, hcp, that encodes a 62 amino acid protein 100% conserved among all strains examined. The gene is restricted exclusively to the picocyano- bacterial lineage. The current study reveals that hcp is also 100% conserved in four freshwater Synechococcus spp. strains isolated from the Laurentian Great Lakes, and that the gene cons- titutively expressed with genes encoding a ribosomal protein and two tRNA genes. The synteny of the hcp region is also conserved between the marine and freshwater strains. Last, the hcp gene and the organization of the surrounding genetic region has been retained in the reduced genome of a picocyanobacterial endosymbiont of the amoeba Paulinella sp. Keywords: Picocyanobacteria / Synechococcus / Hyperconserved protein / Paulinella Received: October 15, 2009; accepted: November 20, 2009 DOI 10.1002/jobm.200900337 Introduction * The autotrophic picoplankton are major primary pro- ducers in both the oligotrophic ocean and in large lakes. Such biomass in both marine and freshwater ecosystems is composed predominantly of cyanobacte- ria < 3 μM in size, including the genera Synechococcus spp. (in marine and freshwaters) and Prochlorococcus spp. (in oligotrophic tropical waters). Whereas a great body of research has been focused on the genetic and physio- logical biodiversity between different picocyanobacte- rial ecotypes in the ocean [1, review], the freshwater picocyanobacteria have received far less attention [2]. Indeed, the ecophysiology and evolution of marine picocyanobacteria has been aided by the vast amount of genomic data currently available for Synechococcus spp. Correspondence: Prof. G.S. Bullerjahn, Department of Biological Sciences, Bowling Green State University, Life Sciences Building, Bowling Green, OH 43403 USA E-mail: bullerj@bgsu.edu Phone: +1-419-372-8527 Fax: +1-419-372-2024 and Prochlorococcus spp., and from these studies, a core picocyanobacterial genome of 1,228 orthologs has been established [3]. Despite their close relatedness to the marine forms, no such comparative genomics is avail- able for the strains inhabiting exclusively freshwater environments. Of the picocyanobacterial core genome, Zhaxybayeva and colleagues identified a conserved gene present in all marine picocyanobacteria, but lacking in the ge- nomes of other cyanobacterial clades [4]. Surprisingly, the gene, termed hcp (for hyperconserved protein), en- codes an invariant polypeptide of 62 amino acid resi- dues. Among these marine taxa, the synteny of the hcp region is highly conserved, in that hcp is located be- tween two tRNA genes that are in turn flanked by rpl19, encoding large ribosomal subunit protein 19 and gltX, encoding a glutamyl tRNA synthetase. Analysis of the deduced amino acid sequence suggested that Hcp is a DNA or RNA binding protein, and its functional parti- tioning with genes involved in translation suggest a role in this process.