Hydrocarbon production in genetically engineered cyanobacteria

蓝藻是一种光合细菌，具有利用太阳能作为能源和二氧化碳作为碳源的转化能力，并且具有易于修饰的基因工程能力，可以构建非天然和改进的天然生物合成途径，在生物技术应用和生物燃料生产方面显示出巨大的潜力。碳氢化合物是汽油、柴油和喷气燃料的主要成分。Schirmer等人在Science（2010）上报道的蓝藻中天然产烃途径的鉴定进一步扩大了蓝藻通过代谢工程进行光合作用生产碳氢化合物的潜力。然而，也存在一些瓶颈需要解决，如脂肪酰基- acp还原酶和脂肪醛脱碳酶活性较低，或者缺乏合适的启动子来有效表达蓝藻产烃途径基因。此外，这一原生产烃途径的生物学功能和控制其表达的调控机制在蓝藻门之外尚未被发现，是完全未知的，但与所得到的化合物的大规模生产具有潜在的相关性。为了显著提高蓝藻的产烃效率，我们提出了以下三个研究任务：(1)通过定向进化筛选催化效率更高的参与产烃途径的改良酶。(2)从蓝藻基因组DNA库中筛选合适的过表达产烃途径基因启动子。(3)分析不同培养条件下蓝藻产烃途径基因的表达模式，确定基因表达的调控因子。

Cyanobacteria, photosynthetic bacteria with conversion capability to utilize solar energy as energy source and carbon dioxide as carbon source and with genetic engineering capacity to be easily modified to build non-native and improved native biosynthetic pathways, have displayed huge potential for biotechnology applications and for the production of biofuels. Hydrocarbons are the predominant constituents of gasoline, diesel, and jet fuels. The identification of a native hydrocarbon-producing pathway in cyanobacteria reported by Schirmer et al. in Science (2010) enlarged the potential for photosynthetic production of hydrocarbons by metabolic engineering in cyanobacteria further. However, there also exist some bottlenecks needed to be addressed, such as the low activities of fatty acyl-ACP reductase and fatty aldehyde decarbonylase or the lack of suitable promoters for the efficient expression of hydrocarbon-producing pathway genes in cyanobacteria. Moreover, the biological function of this native hydrocarbon-producing pathway, which has not been detected outside the cyanobacterial phylum and the regulatoryion mechanisms controlling its expression, are entirely unknown, but of potential relevance for the large-scale production of the resulting compounds.In order to significantly improve the production efficiency of hydrocarbons in cyanobacteria, we propose the following three research tasks:(1) To screen for improved enzymes involved in hydrocarbon-producing pathway with higher catalytic efficiency by directed evolution.(2) To screen the suitable promoters from the genome DNA pools of cyanobacteria for over-expression of hydrocarbon-producing pathway genes.(3) To analyze the expression pattern of cyanobacterial hydrocarbon-producing pathway genes under different culture conditions, and to identify the regulators responsible for gene expression.