The Relationship Between RDNA Intergenic Spacer And The Intrinsic Growth Rates Of Three Ciliate Species

Ciliophora (or ciliates) is a large group with probably the greatest diversity ofcell structures among all eukaryotic microorganisms. In ciliates, cilia are usuallyarranged in longitudinal rows, or formed into undulating memberane,membranelle or cirrus in some species. Ciliates have two kinds of nuclearapparatus: the micronuclei and macronulei. Ciliates are not only uni-cell but alsomicroorganism, and have been ideal model organisma for both cellular andbiological expriments.Due to the importance of ribosomal in protein sybphesis, cellular growth, andorganismal developmebp, ribosomal genes are highly transcribed. We hypothesethat the intrinsic rate of growth is related to the ribosomal RNA gene transcriptionrate. We have determined the intrinsic growth rates of three ciliate species,Paramecium bursaria,Coleps hirtus and Strombidium sulcatum and sequenced thewhole ribosomal gene operon (rrn) which includes18S rRNA gene,the internaltranscribed spacer1, the5.8S rRNA,the internal transcribed spacer2,the28SrRNA gene and the intergenic spacer region (IGS). The possible relationshipsbetween intrinsic growth rates and transcription promoter,sequence length andsubrepeat of rDNA intergenic spacer region were explored.We found that the intrinsic growth rates of Strombidium sulcatum was thehighest among the three ciliates, followed by Paramecium bursaria and Colepshirtus. The lengths of the IGS were2670,3864and4021bp in S. sulcatum, C. hirtusand P.bursaria, respectively. These indicate that the intrinsic growth rates arenvgatively correled with the IGS lengths. We also found that Paramecium bursariacontains more duplications of the core transcription promoter in IGS sequence.Other subreprats were found in IGS of the three species. Theses subrepeats areguite different among species.We show that the rrn operon be quite different in length among ciliate species, and the main differences come from the IGS, which is basically consistent withprevious studies in other eukaryotes. This may imply that IGS could be applied indistuiguishing geographic populations, or closely related species of ciliates. Inaddition, the newly designed and examined primers for amplifying fragments ofthe rDNA sequence in this work should be useful for other ciliate species.