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.