Altered carbohydrate metabolism in glycogen synthase mutants of Synechococcus sp. strain PCC 7002: Cell factories for soluble sugars

Glycogen and compatible solutes are the major polymeric and soluble carbohydrates in cyanobacteria and function as energy reserves and osmoprotectants, respectively. Glycogen synthase null mutants (glgA-I glgA-II) were constructed in the cyanobacterium Synechococcus sp. strain PCC 7002. Under standa...

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Bibliographic Details
Published in:Metabolic engineering 2013-03, Vol.16, p.56-67
Main Authors: Xu, Yu, Tiago Guerra, L., Li, Zhongkui, Ludwig, Marcus, Charles Dismukes, G., Bryant, Donald A.
Format: Article
Language:English
Subjects:
Autofermentation
Bacterial Proteins - genetics
Cyanobacteria
Glucose - biosynthesis
Glucose - genetics
Glycogen
Glycogen Synthase - genetics
Hypersaline
Mutation
Nitrogen limitation
Osmotic Pressure
Photosynthesis
Soluble sugars
Sucrose - metabolism
Synechococcus
Synechococcus - genetics
Synechococcus - metabolism
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Summary:Glycogen and compatible solutes are the major polymeric and soluble carbohydrates in cyanobacteria and function as energy reserves and osmoprotectants, respectively. Glycogen synthase null mutants (glgA-I glgA-II) were constructed in the cyanobacterium Synechococcus sp. strain PCC 7002. Under standard conditions the double mutant produced no glycogen and more soluble sugars. When grown under hypersaline conditions, the glgA-I glgA-II mutant accumulated 1.8-fold more soluble sugars (sucrose and glucosylglycer-(ol/ate)) than WT, and these cells spontaneously excreted soluble sugars into the medium at high levels without the need for additional transporters. An average of 27% more soluble sugars was released from the glgA-I glgA-II mutant than WT by hypo-osmotic shock. Extracellular vesicles budding from the outer membrane were observed by transmission electron microscopy in glgA-I glgA-II cells grown under hypersaline conditions. The glgA-I glgA-II mutant serves as a starting point for developing cell factories for photosynthetic production and excretion of sugars. ► A glycogen synthase null strain accumulated more soluble sugars than the wild type. ► In hypersaline medium glgA mutants produced and excreted more soluble sugars than wild type. ► In hypersaline medium the glgA-I glgA-II mutant produced membrane-enveloped, vesicular structures. ► The effects of nitrogen-starvation were less severe in glgA mutants than in wild type. ► A model predicts that 39% of photosynthetic capacity can be used for biofuels without affecting growth.
ISSN:1096-7176
1096-7184
DOI:10.1016/j.ymben.2012.12.002