COMPOSITE, LARGE SPIROCHETES FROM MICROBIAL MATS - SPIROCHETE STRUCTURE REVIEW

Phenomena previously unknown in free-living spirochetes are reported: large-sized cells with variable diameter (length to 100 mum, width bet ween 0.4 and 3.0 mum), composite structure (smaller spirochetes inside larger ones), and positive phototropic behavior. These bacteria, Spir osymplokos, are compared with all other spirochete genera. The large s pirochete, grown in mixed culture, was studied live and by transmissio n EM. The protoplasmic cylinder was replete with spherical granules 20 -32 nm in diameter, and three to six periplasmic 26-nm flagella were i nserted subterminally. Comparably granulated and flagellated small spi rochetes were located inside the protoplasmic cylinder and in the peri plasm of the large ones. When exposed to air, movement became erratic, protoplasmic cylinders retracted to lie folded inside the outer membr ane, and refractile membranous structures formed. From one to four str uctures per still-moving spirochete were seen. Spirosymplokos was enri ched from laboratory samples exposed to oxygen-rich and desiccating, b ut not dry, conditions for at least 4 mo after removal of microbial ma t from the field.