Conclusion and future perspectives

Even though the role of passive diffusion of fatty acids through membrane is only lately being put into question, the study of fatty acid transport systems during the last years has shed light on several of these systems and their mechanism (Table 2). Differences in membrane structure and divergence of physiological needs cause a wide diversity of fatty acid transport systems. This diversity is reflected on the existence of both single protein systems and multiprotein complexes as well as transport systems with or without acyl-CoA synthetase activity. Furthermore, the higher intracellular complexity of eukaryotic organisms needs the presence of transporters for the organelle membranes and trafficking systems between different hotspots for fatty acid metabolism and storage. Although many proteins involved in the microbial transport of fatty acids have already been identified, there are still important knowledge gaps, such as the transport mechanism of most of these proteins, the identification of fatty acid export proteins for microalgae or the study of fatty acid transport systems in filamentous fungi, such as Aspergillus niger or other model microorganisms such as B. subtilis. Finally, the engineering examples showed in this review are expected to keep increasing in number as more fatty acid transport proteins are identified and their mechanisms are elucidated. This will be an essential step in the optimization of microbial cell factories that consume or produce fatty acids and related compounds.