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The Methanosarcina barkeri Genome: Comparative Analysis with Methanosarcina acetivorans and Methanosarcina mazei Reveals Extensive Rearrangement within Methanosarcinal Genomes ^,

Center of Marine Biotechnology, University of Maryland Biotechnology Institute, Columbus Center, Suite 236, 701 E. Pratt St., Baltimore, Maryland 21202,¹ Microbial Genomics, DOE Joint Genome Institute, 2800 Mitchell Drive, B400, Walnut Creek, California 94598,² DOE Joint Genome Institute, Los Alamos National Laboratory, Los Alamos, New Mexico 87545,³ University of Illinois, Department of Microbiology, B103 Chemical and Life Sciences Laboratory, 601 S. Goodwin Avenue, Urbana, Illinois 61801⁴

Received 7 June 2006/ Accepted 5 September 2006

We report here a comparative analysis of the genome sequence of Methanosarcina barkeri with those of Methanosarcina acetivorans and Methanosarcina mazei. The genome of M. barkeri is distinguished by having an organization that is well conserved with respect to the other Methanosarcina spp. in the region proximal to the origin of replication, with interspecies gene similarities as high as 95%. However, it is disordered and marked by increased transposase frequency and decreased gene synteny and gene density in the distal semigenome. Of the 3,680 open reading frames (ORFs) in M. barkeri, 746 had homologs with better than 80% identity to both M. acetivorans and M. mazei, while 128 nonhypothetical ORFs were unique (nonorthologous) among these species, including a complete formate dehydrogenase operon, genes required for N-acetylmuramic acid synthesis, a 14-gene gas vesicle cluster, and a bacterial-like P450-specific ferredoxin reductase cluster not previously observed or characterized for this genus. A cryptic 36-kbp plasmid sequence that contains an orc1 gene flanked by a presumptive origin of replication consisting of 38 tandem repeats of a 143-nucleotide motif was detected in M. barkeri. Three-way comparison of these genomes reveals differing mechanisms for the accrual of changes. Elongation of the relatively large M. acetivorans genome is the result of uniformly distributed multiple gene scale insertions and duplications, while the M. barkeri genome is characterized by localized inversions associated with the loss of gene content. In contrast, the short M. mazei genome most closely approximates the putative ancestral organizational state of these species.

Published ahead of print on 15 September 2006.

Supplemental material for this article may be found at http://jb.asm.org/.

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