Systematic and Applied Microbiology 34 (2011) 393–399 Contents lists available at ScienceDirect Systematic and Applied Microbiology jo u rn al homepage: www.elsevier.de/syapm Short communication The celC gene, a new phylogenetic marker useful for taxonomic studies in Rhizobium Marta Robledo, Encarna Velázquez ∗ , Martha Helena Ramírez-Bahena 1 , Paula García-Fraile, Ana Pérez-Alonso, Raúl Rivas, Eustoquio Martínez-Molina, Pedro F. Mateos Departamento de Microbiología y Genética, Universidad de Salamanca, Spain a r t i c l e i n f o Article history: Received 15 October 2010 Keywords: celC Phylogeny Taxonomy Endoglucanases Cellulose a b s t r a c t The celC gene codifies for a cellulase that fulfils a very significant role in the infection process of clover by Rhizobium leguminosarum. This gene is located in the celABC operon present in the chromosome of strains representing R. leguminosarum, Rhizobium etli and Rhizobium radiobacter whose genomes have been com- pletely sequenced. Nevertheless, the existence of this gene in other species of the genus Rhizobium had not been investigated to date. In this study, the celC gene was analysed for the first time in several species of this genus isolated from legume nodules and plant tumours, in order to compare the celC phylogeny to those of other chromosomal and plasmidic genes. The results obtained showed that phylogenies of celC and chromosomal genes, such as rrs, recA and atpD, were completely congruent, whereas no relation was found with symbiotic or virulence genes. Therefore, the suitability and usefulness of the celC gene to differentiate species of the genus Rhizobium, especially those with closely related rrs genes, was high- lighted. Consequently, the taxonomic status of several strains of the genus Rhizobium with completely sequenced genomes is also discussed. © 2011 Elsevier GmbH. All rights reserved. Introduction The cellulase genes and the cellulolytic enzymes they encode are widespread and commonly expressed among bacteria estab- lishing root nodule symbiosis [24]. Among them, the celC gene, located near putative cellulose synthase genes in a region of the chromosome (celABC), is involved in bacterial cellulose biosynthe- sis [20]. It codifies for a cellulase essential for symbiotic infection of legume host roots in the genus Rhizobium, thus fulfilling a very significant role in the infection processes required for the devel- opment of nitrogen fixation endosymbiosis [24]. This gene was initially sequenced in several clover-nodulating Rhizobium strains and there were certain problems with its designation, since it has been variously named celC when the complete celABC operon was sequenced in Rhizobium leguminosarum bv trifolii R201 [5], celC8 because it codifies for a protein from glycosidase family 8 in Escherichia coli [4], celY in R. leguminosarum bv viciae 3841 because it codifies for an endo-1,4-beta-glucanase Y in Erwinia chrysanthemi ∗ Corresponding author at: Departamento de Microbiología y Genética, Lab. 209, Edificio Departamental de Biología, Campus Miguel de Unamuno, 37007 Salamanca, Spain. Tel.: +34 923 294532; fax: +34 923 224876. E-mail address: evp@usal.es (E. Velázquez). 1 Present address: Laboratoire de Ecologie Microbienne, Universite Claude Bernard, Lyon, France. [10] and, finally, celC2 because it codifies for a protein named cel- lulase C2 [24]. Nevertheless, currently, celC is the common name used in most of the complete rhizobia genomes sequenced to date, such as Rhizobium radiobacter (formerly Agrobacterium tumefaciens) C58, whose genome was the first completely sequenced for this group of bacteria (accession number of the linear chromosome AE007870). Later, the celC gene was localized in several strains from the genus Rhizobium whose complete sequences have recently been obtained, such as R. leguminosarum bv trifolii WSM1325 and WSM2340 (accession numbers for chromosomes, NC 012850 and NC 011369, respectively), R. leguminosarum bv viciae 3841 (acces- sion number for chromosome, NC 008380), R. etli CFN42 T and CIAT 652 (accession numbers for chromosomes, NC 007761 and NC 010994, respectively) and R. radiobacter (currently Rhizobium rhizogenes) K84 (accession number for chromosome 2, CP000629). Moreover, in the annotations of the complete genome of R. legu- minosarum bv viciae strain 3841, the initial name celY has been changed to celC (accession number for chromosome, NC 008380). In all these strains, the celC gene has a chromosomal location. This gene has not been found in any of the three strains from the genus Bradyrhizobium whose genomes have been sequenced to date: USDA 110, BTAi1, and ORS 278 (accession numbers for chromosomes, NC 004463, NC 009485, NC 009445, respectively), as well as in Azorhizobium caulinodans ORS 571 T (accession num- ber for chromosome, NC 009937), Mesorhizobium loti MAF303099 (accession number for chromosome, NC 002678) or Rhizobium 0723-2020/$ – see front matter © 2011 Elsevier GmbH. All rights reserved. doi:10.1016/j.syapm.2011.01.010