Small Sources of Sweetness

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Science  24 Feb 2012:
Vol. 335, Issue 6071, pp. 892
DOI: 10.1126/science.335.6071.892-b

The sucrose sourced from sugarcane to sweeten our tea and cake—and more recently, to foster ethanol as a transportation fuel—is the same molecule produced by many microorganisms that potentially face fewer cultivation constraints. The trouble is that the microbes don't release their sugar easily. Ducat et al. noted that heterotrophic and autotrophic bacteria induce oppositely directed transmembrane proton gradients, and as such, a gradient-dependent native transporter that pulls sucrose into the former might expel it from the latter. They therefore expressed this sucrose permease in Synechococcus elongatus cyanobacteria—known to produce sucrose under osmotic stress—and indeed collected the sugar in the medium. Furthermore, strains incorporating the transporter manifested enhanced photosynthetic productivity, as assessed by measuring oxygen evolution rates and fixation of 14C-labeled tracers. Though scale-up presents a range of challenges, extrapolation of the laboratory results suggests prospective sucrose productivities on par with or even exceeding that of sugarcane.

Appl. Environ. Microbiol. 78, 10.1128/AEM.07901-11 (2012).

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