title: Expression and Function of Different Guanine-Plus-Cytosine Content 16S rRNA Genes inHaloarcula hispanicaat Different Temperatures.
abstract: The halophilic archaeonHaloarcula hispanicaharbors three ribosomal RNA (rRNA) operons (rrnA,rrnB, andrrnC) that contain the 16S rRNA genesrrsA,rrsB, andrrsC, respectively. AlthoughrrsBandrrsC(rrsBC) have almost identical sequences, therrsAandrrsBCsequences differ by 5.4%, and they differ by 2.5% with respect to guanine-plus-cytosine content (PGC). The strong correlation between the typical growth temperatures of archaea andPGCof their 16S rRNA genes suggests thatH. hispanicamay harbor different 16S rRNA genes having differentPGCto maintain rapid growth in a wide range of temperatures. We therefore performed reverse transcription-coupled quantitative PCR to assess expression levels ofrrsA(PGC, 58.9%) andrrsBC(PGC, 56.4-56.5%) at various temperatures. The expression ratio ofrrsAtorrsBCincreased with culture temperature. Mutants with complete deletions of one or two of the three rRNA operons were constructed and their growth rates at different temperatures compared to that of the wild-type. The growth characteristics of the rRNA operon single-mutant strains were indistinguishable from the wild-type. The rRNA operon double-mutant strains maintained the same temperature range as wild-type but displayed reduced growth rates. In particular, the double-mutant strains grew much slower than wild-type at low temperature related to minimum growth temperature of the wild-type. On the other hand, at physiologically high temperatures the wild-type and the double-mutant strain which harbors onlyrrnAwith high-PGCrrsAgrew significantly faster than the double-mutant strain which harbors onlyrrnCwith low-PGCrrsC. These findings suggest the importance of 16S rRNAs transcribed fromrrsAwith high-PGCin maintaining rapid growth of this halophilic archaeon at raised growth temperatures.
authors.affiliation: Department of Environment and Energy Systems, Graduate School of Science and Technology, Shizuoka University Shizuoka, Japan.
authors.forename: Yu
authors.initials: Y
authors.lastname: Sato
authors.affiliation: Department of Environment and Energy Systems, Graduate School of Science and Technology, Shizuoka UniversityShizuoka, Japan; Department of Biological Science, Faculty of Science, Shizuoka UniversityShizuoka, Japan.
authors.forename: Taketomo
authors.initials: T
authors.lastname: Fujiwara
authors.affiliation: Department of Environment and Energy Systems, Graduate School of Science and Technology, Shizuoka UniversityShizuoka, Japan; Department of Geosciences, Faculty of Science, Shizuoka UniversityShizuoka, Japan; Research Institute of Green Science and Technology, Shizuoka UniversityShizuoka, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kimura
keywords: 16S rRNA genes; Haloarcula; guanine-plus-cytosine content; intragenomic heterogeneity; temperature