一株分离自北极的细菌经可见光照射致死的机理

Strain R3-44 isolated from the surface soil of the Arctic at Ny-Alesund area (N79 ) with the highest 16S rRNA gene sequence similarity 95% with Chitinimonas koreensisthe, a potential new taxa. The strain can grow under aerobic and anaerobic conditions, but under visible light illumination the cultures were white, dark condition, the cultures were yellow-green. The yellow-green cultures will be death during the exposure to visible light in aerobic condition. We plan to explore the killing mechanism of strain R3-44 by visible light from the role and impact of three factors: light - pigments - oxygen. Compare of the genomic sequences of the wild and white mutant strains and mine the differentially transcriptomic profile of wild strain in dark and light conditions to look for key genes of pigment expression, to analysis the metabolic differences in light- and dark-grown cultures, to conjecture the trigger and closing mechanism of the chlorophyll - porphyrin metabolic pathways and the possible adaptation to polar day to polar night. Also, the composition and structure of pigments and porphyrin extracted from strain R3-44 will be studied and to discuss its role and the possibility of as a photosensitizer for photodynamic therapy.

菌株R3-44分离自北极新奥尔松地区（北纬79 ）的表层土壤，其16S rRNA基因与几丁质单胞菌属的Chitinimonas koreensis具有最高同源性95%，是一株潜在的新分类单元，而且具有十分独特的光敏感特性。该菌株是兼性厌氧菌，菌落避光培养呈黄绿色，而光照培养呈白色，移除光照后可恢复成黄绿色。但是，培养获得的黄绿色菌体在有氧条件下进行可见光照射会导致死亡。本研究拟从光-色素-氧三个因素的角度分析其所起的作用和相互间的影响，探究菌株R3-44光致死的成因和机理。并通过对野生和白色突变菌株全基因组序列的比较和光、暗两种培养条件下野生菌的转录差异表达谱，寻找色素表达的关键基因，分析在光和暗培养条件下的代谢差异，推测色素-卟啉代谢途径的触发、关闭机制及其与北极极昼极夜环境的可能适应机理。并对菌株R3-44的色素和卟啉成分及结构进行研究，探讨其功能和作为光敏剂用于光动力学治疗的可能性。

对菌株R3-44进行多项分类学研究，将其定名为Chitinimonas arctica sp. nov.。通过对菌株R3-44及其突变白色菌株R-7可见光照射致死现象分析，发现光的波长越短、能量越高，菌株R3-44和R-7的存活率越低；且在相同条件下，突变株R-7的存活率较野生株R3-44高。实验发现，黄绿色菌株R3-44的卟啉含量是白色突变菌株R-7的两倍，而添加提取的卟啉和色素都能增加突变菌株R-7的可见光致死率。通过色素成分分析发现色素可能是一种新型的类胡萝卜素。对野生和突变菌株进行基因组测序，获得了菌株R3-44的基因组完成图，序列总长度为5,292,479 bp，G + C mol %含量为60.79，基因预测有4594个基因。与突变菌株R-7的基因组进行比对，获得65个差异基因。无论野生型还是突变型菌株都含有卟啉代谢通路基因，经验证并没有产生突变，推测突变株的卟啉积累量减少与基因突变无关，可能与基因的转录调控相关。分别提取光照（L）和黑暗（D）条件下菌株R3-44的RNA进行转录组测序，比较光照和黑暗条件下的基因表达差异，发现有显著表达差异（FDR<0.05且|log2RPKM（L/D）|>1）的基因有860个，注释到KEGG通路中的基因只有166个。通过比对，发现在基因组和转录组中都存在的差异基因有16个，主要是与分泌、次级代谢、转录调控相关的基因以及一些未知基因。由此可见，菌株R3-44的可见光致死现象与卟啉和色素的积累有关。而其在光和暗培养条件下色素与卟啉产生和积累的差异推测与其分泌系统、细胞壁状态、色素代谢和转录调控相关。