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kinA mRNA is missing a stop codon in the undomesticated Bacillus subtilis strain ATCC 6051

¹ Graduate School of Information Science, Nara Institute of Science and Technology, Takayama 8916-5, Ikoma, Nara 630-0192, Japan
² Faculty of Pharmaceutical Sciences, Setsunan University, Nagaotouge 45-1, Hirakata, Osaka 573-0101, Japan

Correspondence
Kazuo Kobayashi
kazuok{at}bs.naist.jp

Several features distinguish laboratory and undomesticated strains of Bacillus subtilis. For example, unlike the laboratory strain 168, the undomesticated strain ATCC 6051 is deficient in sporulation in a rich sporulation medium, 2x SG. ATCC 6051 cannot induce transcription of the spoIIG operon, suggesting that this strain has a defect in initiation of sporulation. To determine the genetic difference between 168 and ATCC 6051, the DNA region responsible for the Spo^– phenotype was transferred to strain 168. Genetic mapping and DNA sequencing analysis revealed that a stop codon (TAA) for kinA in 168 is replaced with Lys (TAT) in ATCC 6051, making the kinA open reading frame 201 bp longer in the undomesticated strain ATCC 6051. Introduction of kinA from strain 168 restored sporulation in ATCC 6051, indicating that the difference in kinA is responsible for the Spo^– phenotype of ATCC 6051. A potential -independent terminator is located upstream of a stop codon for the extended kinA open reading frame in ATCC 6051. Northern blot analysis showed that transcription of kinA terminated at this terminator, and kinA mRNA is missing a stop codon in ATCC 6051. Moreover, deletion of tmRNA suppresses the sporulation defect in ATCC 6051. These observations indicate that in ATCC 6051 the absence of a stop codon in kinA mRNA affects sporulation, probably by leading to rapid degradation of KinA via the trans-translation process. In ATCC 6051, the kinA mutation affects sporulation but not other Spo0A-dependent phenomena such as biofilm formation, which can be activated by a low level of Spo0AP. This is due to the fact that KinA activity is kept low during the exponential phase via transcriptional and post-translational regulation. Thus, the stop-codon-less kinA probably affects only sporulation. DNA sequencing of 30 B. subtilis strains revealed that another strain also produces stop-codon-less kinA mRNA. This observation suggests that the lack of a stop codon for kinA mRNA may give rise to a selective advantage under certain conditions.

Two supplementary tables are available with the online version of this paper.