Effect of external environmental factors on the morphology of Spiroplasma citri.

Spiroplasma citri was examined by electron microscopy for morphological changes when maintained under a variety of conditions. PPLO serum fraction maintained spiral and helical morphology of S. citri at pH values of 8.0, 7.5, and 7.0, but only partially at pH 6.0 and 5.0. The absence of PPLO serum fraction resulted in round, deteriorated cells at all pH values tested. Bovine serum albumin (BSA), Phytone, soluble starch, potato starch, spermine, lipid-extracted PPLO serum fraction, and lipid-extracted BSA could substitute for PPLO serum fraction in maintaining spiral and helical morphology at pH 7.5. At pH 5.0, only BSA, lipid-extracted BSA, and lipid-extracted PPLO serum fraction were effective. Only BSA supported growth of S. citri for more than two transfers, whereas all other substitutes could not support growth longer than two transfers.