Those of you who imbibe likely already know that yeast are capable of producing alcohol and carbon dioxide in a process called fermentation. The yeast don't really give a shit about either of these two byproducts; to them, all that is important is that substrate-level phosphorylation generates enough ATP for them to be alive. Thus, slight genetic modifications allow these microfungi to produce something more pleasant-smelling than alcohol. You know, stuff you might want to make perfume out of.
Although only a limited number of fragrances are currently produced in this manner, scientists are working to expand the percentages of the over 6400 natural and 10000 synthetic fragrance compounds that can be generated using synthetic biology. Independent companies such as Evola, Isobionics, and Allylix are working to expand the collection of microbially-produced scents. Their current projects include smells ranging from saffron to valencene, a citrus odorant.
My personal concerns are more mundane. Vanillin, the phenolic aldehyde gives vanilla its principle aroma and taste, has been chemically produced from molecules like eugenol, a component of clove essential oil, or guaiacol since the 1920s. However, it doesn't take a master chef to know that buying "vanillin" at the grocery store will give you only a faint shadow of pure vanilla extract. Vanilla extract contains hundreds of compounds on top of vanillin. Although chemically produced vanillin costs about $12 per 1 kg-1, as compared to $4000 per 1 kg-1 for vanilla that was extracted from vanilla pods, the price difference, to me, seems justified given that these two products provide such different sensory experiences. I worry that, as a relatively new industry, genetically modified yeast won't be used to provide truly complex scent profiles for perfume. And seriously, who wants to buy a bottle of boring perfume? (That being said, I'll be happy to be proven wrong.)