Characterization and expression of Saprospira cytoplasmic fibril protein (SCFP) gene from algicidal Saprospira spp. strains

The Saprospira sp. strain SS98-5 cells form colonies on a nutrient-rich agar medium, but are motile by gliding under low-nutrient condition and then numerous microtubule-like fibril structures are found intracellularly. The fibril structures are composed of a proteinous subunit SCFP; this gene was cloned previously. Here, the organization of ORFs adjacent to the SS98-5 SCFP gene and its transcription were investigated, and a SCFP gene homolog was cloned from Saprospira sp. SS03-4, a relative strain of SS98-5. The SCFP gene was also encoded within the SS03-4 chromosome, and grouped into a phage tail sheath protein family, suggesting its bacteriophage genome origin. Four ORFs adjacent to the SCFP gene were identified and their organization was in common with several prokaryotes. The SCFP mRNA was detected by reverse transcriptase polymerase chain reaction from gliding and non-gliding cells, implying that the SCFP gene was transcribed independent of existence or absence of the fibril structures.