Abstract
Starmerella bombicola is a non-conventional yeast mainly known for its capacity to produce high amounts of the glycolipids ‘sophorolipids’. Although its product has been used as biological detergent for a couple of decades, the genetics of S. bombicola are still largely unknown. Computational analysis of the yeast’s genome enabled us to identify 254 putative transporter genes that make up the entire transportome. For each of them, a potential substrate was predicted using homology analysis, subcellular localization prediction and RNA sequencing in different stages of growth. One transporter family is of exceptional importance to this yeast: the ATP Binding Cassette (ABC) transporter Superfamily, because it harbors the main driver behind the highly efficient sophorolipid export. Furthermore, members of this superfamily translocate a variety of compounds ranging from antibiotics to hydrophobic molecules. We conducted an analysis of this family by creating deletion mutants to understand their role in the export of hydrophobic compounds, antibiotics and sophorolipids. Doing this, we could experimentally confirm the transporters participating in the efflux of medium chain fatty alcohols, particularly decanol and undecanol, and identify a second sophorolipid transporter that is located outside the sophorolipid biosynthetic gene cluster.
Highlights
Phospholipid-based cell membranes facilitate the possibility of cellular life, but at the same time create the need for the cell to access to the exterior environment; this need is provided for by membrane transporter proteins
Identification of the S. bombicola transportome The 4626 predicted protein sequences in the S. bombicola genome were scanned with the transporter identification pipeline [17]. 254 genes were identified as putative transporter genes and subsequently subjected to sequencebased functional grouping: 180 genes were found to be of the type ‘channels’ (TC.1), 24 of the type ‘carrier’ (TC.2)
Mapping the expression profile of the S. bombicola transportome It is unlikely that the entire transportome is present in the yeast cell’s membrane at any given time
Summary
Phospholipid-based cell membranes facilitate the possibility of cellular life, but at the same time create the need for the cell to access to the exterior environment; this need is provided for by membrane transporter proteins. Their crucial roles range from nutrient uptake to export of undesired product, from cell volume control to extracellular nutrient sensing and much more [1]. Carriers (TC.2) bind their substrate and catalyze its crossing after conformational change without the need for utilization of a primary source of energy. The largest and bestknown superfamily within this class is the Major Facilitator Superfamily (MFS) of transporters [7] They are single-polypeptide secondary carriers involved in symport, antiport or uniport of a vast array of substrates, across all kingdoms of life. Mechanisms of bulk transport via endocytosis/exocytosis and intracellular trafficking are not included in the TCDB and are not discussed in this manuscript
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