| Summary: | Bacterial spheroplasts do not divide but they grow and enlarge with DNA replication in a broth containing an inhibitor of peptidoglycan synthesis and high salt concentration. The enlarged spheroplasts of <em>Lelliottia amnigena</em>, belonging to the family Enterobacteriaceae, formed vacuole-like structures, while those of the aerobic photosynthetic marine bacterium <em>Erythrobacter litoralis</em> did not form such structures. In addition, the enlarged spheroplasts of <em>L. amnigena</em>, which differ in the size of inner and outer membranes, were larger than those of <em>E. litoralis</em>. To elucidate the reason for these differences, we analyzed the transcriptome (RNA-seq) of spheroplasts at the beginning of growth and upon enlargement. After sequencing the RNAs expressed in normal and enlarged spheroplasts, we compared the gene expression levels of the 1100 orthologs in <em>E. litoralis</em> and <em>L. amnigena</em>. Among these, 347 and 213 genes were more than 2-fold upregulated in enlarged spheroplasts of <em>E. litoralis</em> and <em>L. amnigena</em>, respectively; 193 and 269 genes were less than 0.5-fold downregulated in those of <em>E. litoralis</em> and <em>L. amnigena</em>, respectively. Thirty six genes were upregulated in <em>L. amnigena</em> enlarged spheroplasts but were downregulated in <em>E. litoralis</em> enlarged spheroplasts, and may be related to vacuole-like structure generation. Fourteen of the 36 genes encoded a membrane protein. Our findings indicate that spheroplast enlargement varies between different organisms with respect to gene expression.
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