Malassezia are very picky eaters. They can’t grow if given only short fatty acids, probably because they can’t elongate them to build their plasma membranes. Malassezia restricta and Malassezia globosa—the main species found in humans—can’t convert saturated fats into unsaturated ones (Celis 2017):
“The observation that the atypical M. furfur cannot grow in MM with Tween 20, 40, and 60, the donors of C12:0, C16:0, and C18:0 fatty acids, respectively, suggests that these saturated fatty acids can not be further elongated and / or desaturated. All strains except M. furfur and the atypical variant were not able to grow in MM supplemented with a single Tween or with fatty acid species, whereas they did grow in mDixon. This observation might be explained if we assume that the strains require a mixture of saturated and unsaturated fatty acids, as was similarly observed with fasl, olel (FAS and fatty acid desaturase minus) mutants of S. cerevisiae. Further analysis showed that the atypical M. furfur and M. pachydermatis indeed was capable to grow or survive in MM with a mixture of palmitic acid and oleic acid.”
Malassezia’s plasma membrane is composed of four main fatty acid types (Porro 1976)—C16:0, C18:0, C18:1 and C18:2—which are probably essential for their growth and survival. It is very difficult to get Malassezia restricta and Malassezia globosa to grow in vitro, probably because they need to be provided the right ratios of different fat types. When provided with only saturated or unsaturated fats, certain Malassezia species fail to grow (Celis 2017):
“It is tempting to speculate that individual fatty acids create an imbalance in the fatty acid compositions of lipids and affect the integrity of the membranes and / or membrane-protein interactions, thereby compromising essential membrane functions. Indeed, palmitic acid affected cell integrity since microscopic observations revealed strong reduction of intact cells (data not shown). The fact that the fungistatic fatty acid oleic acid is antagonistic to the fungicidal activity of palmitic acid suggests that oleic acid blocks a process that leads to cell death and lysis. More research is required to elucidate the mechanisms of how fatty acids interfere or stimulate fungal growth, which is especially relevant considering the variation in lipid sources in the natural environment.”
Very little research has been done so far to elucidate Malassezia’s lipid requirements. Studies focusing on the two Malassezia species commonly present in humans should be run to determine if dietary changes can skew fatty acid ratios inside our bodies to impede Malassezia’s growth. For example, I suspect availability of C18:0 (the main component of glycerol monostearate and Tween 60) might be one of the factors limiting their growth (Kaneko 2005):
“[...] ox bile, glycerol monostearate, glycerol and Tween 60 would appear to be essential components of LNA required for the development of these yeastlike fungi.”
This post was largely based on Celis 2017.
Animated Malassezia and lipids video: https://youtu.be/u1pckKEkwF0
