Microorganisms are believed to be a promising feedstock for the production of many by-products (lactic acid, single cell proteins, bioethanol, polyunsaturated fatty acids) that can resolve the putative problems and cover a wide range of industrial applications. Among these components, polyhydroxyalkanoates (PHA) and fatty acids (FA) are seen as typical materials for more studies and production. In fact, PHA and FA biosynthesis share the same metabolism, where (R)-3-hydroxyacyl-CoA is a common intermediate that resulted from beta-oxidation. Under this directive, FA metabolism is considered as versatile pool for PHA, hence many efforts have been focussed on directing the metabolism of microorganisms for the production of one of the components in question. In fact, the choice of final product is assumed to be a balance between genetic and metabolic regulation. Thus, special attention has been paid in this review for the ongoing research on FA or PHA production and the potential metabolic routes enhancing lipid production have also been extensively discussed. (C) 2014 Elsevier Ltd. All rights reserved.