Arginine metabolism by the corn stunt spiroplasma

Abstract

When corn stunt spiroplasma (CSS) was grown in spiroplasma medium A (SMA) containing 5% horse serum, 16% sucrose, 1.5% PPLO broth, and 0.002% phenol red indicator, color and pH of the medium changed from red (pH 7.5) to yellow (pH 5.8) by 4 days after inoculation with CSS. In spiroplasma medium B (SMB), identical to SMA except for supplementation with 47 mM arginine-HCl, color and pH changed within 4 days but reverted to red (pH 7.5) 6 days later, suggesting that arginine was metabolized. Growth of CSS in both SMA and SMB was a characteristic sigmoid pattern; maximum titers were reached the fifth day after inoculation and were 2.3 × 10⁸ cells/ml in SMA and 4.5×10⁸ cells/ml in SMB. Helicity and motility of CSS were lost after 8 days in SMA, while in SMB some cells were still helical and motile up to 15 days. Daily analyses of CSS cultures by photometric methods showed that arginine was depleted from SMB and production of ammonia and ornithine was higher in SMB than in SMA; citrulline was detected in SMB but urea was not found in either medium. Results from additional tests using an amino acid analyzer and thin-layer chromatography further substantiated arginine metabolism and indicated that an arginine deiminase pathway was operative in CSS.