Large Symbiotic Spirochetes: Clevelandina, Cristispira, Diplocalyx, Hollandina, and Pillotina

Abstract

The genera Cristispira, Clevelandina, Diplocalyx, Hollandina, and Pillotina are morphologically complex, Gram-negative, motile, spirochetes (helical bacteria) in which the flagella are always entirely periplasmic (i.e., located between the inner [plasma] and the outer membrane typical of Gram-negative bacteria) (Fig. 1). (For a general discussion of the morphology of spirochetes, see Chapter 191.) All are obligate symbionts in the digestive system of mollusks or arthropods. These morphologically complex spirochetes have greater than 10 and sometimes as many as 300 flagella inserted at both ends of the cell and overlapping in the middle. If n is the number of flagella at one end of the cell and 2n the number of overlapping flagella in the middle of the cell, then the characteristic array is n:2n:n (e.g., 10:20:10 or 300:600:300). The coated membranes, distinctive cytoplasmic structures (including the sillon, a cell-length invagination or groove of the outer membrane in contact with the inner membrane), and relative proportions that distinguish these genera are depicted in Fig. 2, based on the morphometric analyses summarized in Table 1.