In many organisms, mevalonate synthesis, which is an early step in terpenoid biosynthesis, is a key point of regulation [28] of the corresponding pathway. This is probably also true for fungi, including X. dendrorhous. In fact, addition of mevalonate to a culture of X. dendrorhous stimulated both astaxanthin and total carotenoid biosynthesis four times [29]. This indicates that the conversion of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) to mevalonate by HMG-CoA reductase is a potential bottleneck on the road to modified strains with higher astaxanthin content. Recent examples of enhanced carotenoid accumulation and increased levels of HMG-CoA reductase (as well as HMG-CoA synthase) messenger RNA have been published for