Li Xiaoqian, Shen Claire R, Liao James C
Department of Chemical and Biomolecular Engineering, University of California Los Angeles, Los Angeles, CA, 90095, USA.
Photosynth Res. 2014 Jun;120(3):301-10. doi: 10.1007/s11120-014-9987-6. Epub 2014 Mar 4.
Glycogen synthesis initiated by glucose-1-phosphate adenylyltransferase (glgC) represents a major carbon storage route in cyanobacteria which could divert a significant portion of assimilated carbon. Significant growth retardation in cyanobacteria with glgC knocked out (ΔglgC) has been reported in high light conditions. Here, we knocked out the glgC gene and analyzed its effects on carbon distribution in an isobutanol-producing strain of Synechococcus elongatus PCC7942 and its parental wild-type strain. We showed that isobutanol production was able to partially rescue the growth of ΔglgC mutant where the growth rescue effect positively correlated with the rate of isobutanol production. Using NaH(14)CO3 incorporation analysis, we observed a 28 % loss of total carbon fixation rate in the ΔglgC mutant compared to the wild-type. Upon expression of the isobutanol production pathway in ΔglgC mutant, the total carbon fixation rate was restored to the wild-type level. Furthermore, we showed that 52 % of the total carbon fixed was redirected into isobutanol biosynthesis in the ΔglgC mutant expressing enzymes for isobutanol production, which is 2.5 times higher than that of the wild-type expressing the same enzymes. These results suggest that biosynthesis of non-native product such as isobutanol can serve as a metabolic sink for replacing glycogen to rescue growth and restore carbon fixation rate. The rescue effect may further serve as a platform for cyanobacteria energy and carbon metabolism study.
由葡萄糖-1-磷酸腺苷酰转移酶（glgC）启动的糖原合成是蓝藻中主要的碳储存途径，该途径可转移相当一部分同化碳。据报道，在高光条件下，敲除glgC（ΔglgC）的蓝藻生长显著迟缓。在此，我们敲除了glgC基因，并分析了其对产异丁醇的聚球藻PCC7942菌株及其亲本野生型菌株中碳分布的影响。我们发现，异丁醇的产生能够部分挽救ΔglgC突变体的生长，且生长挽救效应与异丁醇产生速率呈正相关。通过NaH(14)CO3掺入分析，我们观察到与野生型相比，ΔglgC突变体的总碳固定率损失了28%。在ΔglgC突变体中表达异丁醇产生途径后，总碳固定率恢复到了野生型水平。此外，我们还表明，在表达异丁醇产生酶的ΔglgC突变体中，52%的固定总碳被重新导向异丁醇生物合成，这比表达相同酶的野生型高2.5倍。这些结果表明，非天然产物如异丁醇的生物合成可作为一种代谢库来替代糖原，从而挽救生长并恢复碳固定率。这种挽救效应可能进一步成为蓝藻能量和碳代谢研究的一个平台。
