Microorganisms are promising as producers of various polyunsaturated fatty acids (PUFAs) and as catalysts transforming them into unique molecular species beyond common PUFAs. This article describes PUFA production through chemical mutant- and molecular-breeding of an oleaginous filamentous fungus Mortierella alpina 1S-4 and PUFA transformation by anaerobic bacteria. M. alpina 1S-4 and its mutants and transformants produce oils containing not only common n − 6 and n − 3 PUFAs but also rare PUFAs. Unique PUFA-transforming activities were found in anaerobic bacteria. They isomerized PUFA to conjugated fatty acids and further transformed to partially saturated fatty acids with hydroxyl fatty acids as intermediates. The functions of these unique PUFAs have been attracting much attention for improving our health and for developing new chemical materials.