title: Transcriptomic analysis of a moderately growing subisolate Botryococcus braunii 779 (Chlorophyta) in response to nitrogen deprivation.
abstract: BACKGROUND
  The colonial microalga Botryococcus braunii has been brought to people's attention for its conspicuous ability to accumulate a variety of lipids including hydrocarbons. B. braunii strains are classified into 3 races based on the types of hydrocarbons. A and B races are known to accumulate high level of lipids. However, their extreme slow growth rate has impeded its application for renewable biofuel production.
  
  
  RESULTS
  In this study, we report the transcriptomic response of a moderately growing subisolate from the culture of Botryococcus sp. CCALA-779 upon nitrogen deprivation (ND). We show that the subisolate has an average growth rate of 0.52 g l(-1) day(-1) under photoautotrophic growth conditions and lipid content is enhanced to 75 % of CDW upon ND. Both rDNA sequence and hydrocarbon composition analyses indicate that the subisolate belongs to A race B. braunii. Hence, it is designated as B. braunii 779. We show that B. braunii 779 transcriptome shares homology to majority of the A race but not B race B. braunii ESTs, suggesting that transcriptomes of A race differ from that of B race. We found that many homologous ESTs between A races 779 and Bot-88 are unknown sequences, implying that A race contains many unknown genes. Pathway-based transcriptomic analysis indicates that energy metabolisms are among the top expressed functions in log-phase cells, indicating that the slow growth rate is a result that energy flow is directed to lipid biosynthesis but not population growth. Upon ND, reconfiguration of metabolisms for reducing power is apparent, suggesting that B. braunii 779 is rapidly adapting under ND condition by transcriptomic reprogramming.
  
  
  CONCLUSIONS
  Taken together, our result shows that the subisolate B. braunii 779, similar to the Gottingen strain, is useful for biofuel production. Difference between transcriptomes of A and B races implies that different races of B. braunii strains belong to different sub-species. Furthermore, there are many novel genes that are unique to A race, suggesting that sequences of many enzymes involved in hydrocarbon biosynthesis are not currently known. We propose that B. braunii transcriptomes provide a rich source for discovery of novel genes involved in hydrocarbon biosynthesis.
authors: Collaborative Innovation Center of Deep Sea Biology, Ocean College, Zhejiang University, Hangzhou, 310058 Zhejiang China.|Dalian Ocean University, Dalian, 116023 Liaoning China.
authors: Lei
authors: L
authors: Fang
authors: Genome Institute of Singapore, A-STAR, Singapore, 138672 Singapore.|Biopolis Shared Facilities, A-STAR, Singapore, 138671 Singapore.
authors: Deying
authors: D
authors: Sun
authors: Collaborative Innovation Center of Deep Sea Biology, Ocean College, Zhejiang University, Hangzhou, 310058 Zhejiang China.
authors: Zhenyu
authors: Z
authors: Xu
authors: Ocean Research Centre of Zhoushan, Zhejiang University, 10 Tiyu Road, Room 502, Zhoushan, 316021 Zhejiang China.
authors: Jing
authors: J
authors: He
authors: Collaborative Innovation Center of Deep Sea Biology, Ocean College, Zhejiang University, Hangzhou, 310058 Zhejiang China.
authors: Shuyuan
authors: S
authors: Qi
authors: Zhejiang Provincial Key Laboratory for Microbial Biochemistry and Metabolic Engineering and College of Life Sciences, Zhejiang University, Hangzhou, 310058 Zhejiang China.
authors: Xin
authors: X
authors: Chen
authors: Institute of Chemical and Engineering Sciences, A-STAR, Singapore, 627833 Singapore.
authors: Wee
authors: W
authors: Chew
authors: Collaborative Innovation Center of Deep Sea Biology, Ocean College, Zhejiang University, Hangzhou, 310058 Zhejiang China.|Ocean Research Centre of Zhoushan, Zhejiang University, 10 Tiyu Road, Room 502, Zhoushan, 316021 Zhejiang China.
authors: Jianhua
authors: J
authors: Liu
keywords: Botryococcus braunii; Green microalgae; Hydrocarbon; Response to nitrogen deprivation; Transcriptome