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Microbiology Society logo - Volume 160, Issue 7, 2014

Volume 160, Issue 7

Volume 160, Issue 7, 2014

 EDITOR'S CHOICE:
  • Physiology and Biochemistry

      • Identification of a novel ATP-binding cassette transporter involved in long-chain fatty acid import and its role in triacylglycerol accumulation in RHA1

        https://doi.org/10.1099/mic.0.078477-0

        Members of the genus are specialists in the biosynthesis and accumulation of triacylglycerols (TAGs). As no transport protein related to TAG metabolism has yet been characterized in these bacteria, we used the available genomic information of RHA1 to perform a broad survey of genes coding for putative lipid transporter proteins in this oleaginous micro-organism. Among the seven genes encoding putative lipid transporters, (now called : lipid transporter protein) coding for an ATP-binding cassette protein was found clustered with others genes encoding enzymes catalysing the three putative acylation reactions of the Kennedy pathway for TAG synthesis. Overexpression of in the RHA1 strain led to an increase of approximately sixfold and threefold in biomass and TAG production, respectively, when cells were cultivated on palmitic acid and oleic acid. Moreover, overexpression of also promoted a significant increase in the uptake of a fluorescently labelled long-chain fatty acid (LCFA), as compared with the WT strain RHA1, and its further incorporation into the TAG fraction. Gluconate-grown cells showed increasing amounts of intracellular free fatty acids, but not of TAG, after overexpressing . Thus, for the first time to our knowledge, a transporter functionally related to TAG metabolism was identified in oleaginous rhodococci. Our results suggested that Ltp1 is an importer of LCFAs that plays a functional role in lipid homeostasis of RHA1.

    • A Na-coupled C-dicarboxylate transporter (Asuc_0304) and aerobic growth of on C-dicarboxylates

      https://doi.org/10.1099/mic.0.076786-0

      , which is known to produce large amounts of succinate during fermentation of hexoses, was able to grow on C-dicarboxylates such as fumarate under aerobic and anaerobic conditions. Anaerobic growth on fumarate was stimulated by glycerol and the major product was succinate, indicating the involvement of fumarate respiration similar to succinate production from glucose. The aerobic growth on C-dicarboxylates and the transport proteins involved were studied. Fumarate was oxidized to acetate. The genome of encodes six proteins with similarity to secondary C-dicarboxylate transporters, including transporters of the Dcu (C-dicarboxylate uptake), DcuC (C-dicarboxylate uptake C), DASS (divalent anion : sodium symporter) and TDT (tellurite resistance dicarboxylate transporter) family. From the cloned genes, Asuc_0304 of the DASS family protein was able to restore aerobic growth on C-dicarboxylates in a C-dicarboxylate-transport-negative strain. The strain regained succinate or fumarate uptake, which was dependent on the electrochemical proton potential and the presence of Na. The transport had an optimum pH ~7, indicating transport of the dianionic C-dicarboxylates. Transport competition experiments suggested substrate specificity for fumarate and succinate. The transport characteristics for C-dicarboxylate uptake by cells of aerobically grown were similar to those of Asuc_0304 expressed in , suggesting that Asuc_0304 has an important role in aerobic fumarate uptake in . Asuc_0304 has sequence similarity to bacterial Na-dicarboxylate cotransporters and contains the carboxylate-binding signature. Asuc_0304 was named SdcA (odium-coupled C-iarboxylate transporter from . ).

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