拟柱孢藻N8全基因组测序及磷吸收转运通路的比较分析

WHOLE-GENOME SEQUENCING AND PHOSPHORUS UPTAKE AND TRANSPORT PATHWAY COMPARATIVE ANALYSIS OF CYLINDROSPERMOPSIS RACIBORSKII N8

为从分子水平解析热带特征性蓝藻-拉氏拟柱孢藻(Cylindrospermopsis raciborskii,简称拟柱孢藻)环境适应机制,研究以广东省镇海水库中分离的拟柱孢藻藻株N8为材料,采用PacBio单分子实时测序技术(Single Molecule Real-Time, SMRT)进行测序,并初步进行全基因组特征的比较分析。结果显示拟柱孢藻N8全基因组大小为3.857 Mb, GC含量为40.13%,预测编码基因个数为3598个,在COG、KEGG和GO数据库中注释到的基因数分别为2429、1664和2244个。N8藻株与美国国立生物技术信息中心(NCBI)上公布的27株拟柱孢藻基因组大小和GC含量基本一致,但N8的编码基因数最多。基于拟柱孢藻全基因组单拷贝基因的系统进化树表明N8藻株与韩国藻株GIHE 2018的亲缘关系最近。N8藻株的基因组中未发现拟柱孢藻毒素(CYN)和石房蛤毒素(STX)合成酶基因簇,表明该藻株不产蓝藻毒素CYN和STX。对N8藻株和其他7藻株的磷吸收转运通路比较分析表明,这些藻株均拥有较为完整的磷吸收转运基因(双组分调节系统、低亲和力无机磷转运基因、高亲和力无机磷转运系统、有机磷酸盐转运复合体、C-P裂解酶和碱性磷酸酶),表明拟柱孢藻具有灵活利用环境中不同形态磷源的潜能;而不同藻株间的基因拷贝数和排列顺序存在差异,如拟柱孢藻N8基因组中有2个C-P裂解酶复合体蛋白phnF和phnM,其余7株拟柱孢藻则只有1个,表明拟柱孢藻存在株系特异性。N8藻株为中国首株公开完成全基因组测序数据的拟柱孢藻,对其基因组分析和磷吸收转运通路的解析将有助于阐明华南地区拟柱孢藻水华优势形成的分子机制。

Tropical cyanobacterium Cylindrospermopsis raciborskii have attracted much attention due to their rapid expansion into temperate regions.Studies on understanding the genomic characteristics will help analyze their environmental adaptation mechanisms at the molecular level.The genome of C.raciborskii N8 isolated from Zhenhai Reservoir in Guangdong Province was sequenced using PacBio single-molecule real-time sequencing technology,SMRT,and then performed comparative analysis of the whole genomic characteristics.It was shown that genome size of the strain N8 was 3.857 Mb with 40.13%GC content,similar to other 27 C.raciborskii strains in NCBI databases.Further annotation predicted 3598 protein coding genes,representing the largest number among the published genome data.The number of genes annotated in COG,KEGG and GO databases were 2429,1664 and 2244 respectively.The phylogenetic tree constructed with a single copy gene of the whole genome indicated that C.raciborskii N8 was the most closely related to strain CR12 from Singapore.We inferred that C.raciborskii N8 did not produce toxin cylindrospermopsin(CYN)and saxitoxin(STX)due to the absence of biosynthesis gene cluster for both toxins in its genome.Through examining the genomes of N8 and other 7 strains,we found that these strains had relatively complete phosphorus(P)uptake and transport pathway genes(two-component regulation system,low affinity inorganic P transport gene,high affinity inorganic P transport system,organic phosphonate transport complex,C-P lyase and alkaline phosphatase).This finding demonstrated that C.raciborskii has the potential to utilize different P forms in the ambient environment.However,differences in gene copy number and arrangement among these strains were observed,for example,two C-P lyase complex proteins genes(phnF and phnM)were found in the genome of C.raciborskii N8,while only one in the other 7 strains,indicating variation in C.raciborskii strains.This study represented the first reported whole genome of Chinese C.raciborskii strain.The analysis of its genomic characteristics and P metabolism pathway will help clarify the winning strategies of C.raciborskii in South China.