This study examined the fatty acid requirements of Pityrosporum ovale, a lipophilic yeast isolated from human scalp. Using defined media and radioactive tracers, the researchers determined that P. ovale requires exogenous fatty acids because it cannot synthesize myristic acid (C14). Myristic or palmitic acid alone supports growth, while oleic acid increases growth when combined with limiting concentrations of either saturated fatty acid. When P. ovale was cultured with radioactively labeled myristic acid, the organism accumulated myristate, palmitate, stearate, oleate, and linoleate with similar radioactivity, indicating synthesis of higher fatty acids through chain elongation from myristate. Using radioactive stearic acid, the researchers demonstrated that P. ovale can convert stearic acid to oleic acid, though this pathway may be less efficient than in other organisms. The findings revealed that P. ovale's fatty acid auxotrophy stems specifically from an inability to synthesize C14 and C16 saturated fatty acids de novo, while possessing functional elongase and desaturase enzymes for modifying exogenously supplied fatty acids.

Key findings

• Pityrosporum ovale requires exogenous C14 (myristic) or C16 (palmitic) saturated fatty acids for growth due to inability to synthesize these compounds de novo
• Oleic acid spares the requirement for saturated fatty acids, increasing organism yield when added to media containing limiting concentrations of myristic or palmitic acid
• P. ovale synthesizes higher molecular weight saturated and unsaturated fatty acids from exogenous myristic acid via chain elongation, as demonstrated by radioactive labeling experiments showing similar specific radioactivity in myristate, palmitate, stearate, oleate, and linoleate
• Stearic acid can be converted to oleic acid in P. ovale, though this pathway may be less efficient than oleate supplementation
• P. ovale is unique among microorganisms in requiring C14 or C16 saturated fatty acids, reflecting a specific biosynthetic block in fatty acid synthesis