CAJ | 학술논문

胞外多糖(EPS)是结皮蓝藻形成生物结皮的胶结剂,为了理解常球状存在的丝状蓝藻--Nostoc 胶结沙粒的机理,探讨了光强[40、80μE/(m2?s)]和氮源(气态氮,硝态氮)对结皮优势种Nostoc sp.分泌EPS(包括荚膜多糖CPS和释放多糖RPS)的影响规律及其内在机理。结果发现：Nostoc sp.在气态氮和硝态氮下都有相似的快速生长,但其分泌的RPS、CPS及EPS量,在硝态氮下均随光强的增加而增加,在气态氮下却与光强没有关系。相关代谢研究发现,在硝态氮下细胞内有更高含量的可溶性糖和蔗糖。进一步的相关分析发现,在两种氮源下,蔗糖量与RPS量或CPS量间的显著正相关都只发生在80μE/(m2?s)下,在气态氮中,两光强下的胞内总糖量都与CPS量显著负相关。以上结果说明, Nostoc sp.在氮源利用和光强适应方面都有明显优势,它即使在快速生长的对数期,也可同时分泌相当量的 EPS,这使其在球状藻殖段形成之前胶结沙粒成为可能。由此可推知, Nostoc sp.在贫瘠沙土表面的最初生长过程中,其胞外的EPS均来自胞内的固碳产物,在高光强下,蔗糖很可能是其EPS合成的原料。
포외다당(EPS)시결피람조형성생물결피적효결제,위료리해상구상존재적사상람조--Nostoc 효결사립적궤리,탐토료광강[40、80μE/(m2?s)]화담원(기태담,초태담)대결피우세충Nostoc sp.분비EPS(포괄협막다당CPS화석방다당RPS)적영향규률급기내재궤리。결과발현：Nostoc sp.재기태담화초태담하도유상사적쾌속생장,단기분비적RPS、CPS급EPS량,재초태담하균수광강적증가이증가,재기태담하각여광강몰유관계。상관대사연구발현,재초태담하세포내유경고함량적가용성당화자당。진일보적상관분석발현,재량충담원하,자당량여RPS량혹CPS량간적현저정상관도지발생재80μE/(m2?s)하,재기태담중,량광강하적포내총당량도여CPS량현저부상관。이상결과설명, Nostoc sp.재담원이용화광강괄응방면도유명현우세,타즉사재쾌속생장적대수기,야가동시분비상당량적 EPS,저사기재구상조식단형성지전효결사립성위가능。유차가추지, Nostoc sp.재빈척사토표면적최초생장과정중,기포외적EPS균래자포내적고탄산물,재고광강하,자당흔가능시기EPS합성적원료。
Extracellular polysaccharides (EPS) play an essential role in adhesion for crust cyanobacteria to form the biological soil crust. The mechanisms of how the normally ball-shape filamentous cyanobacteria Nostoc sp. cements sand grains remains to be elucidated. To understand the mechanisms we investigated the effects of light intensity and nitrogen source on the the secretion of EPS [including releleased exopolysaccharides (RPS) and capsular polysaccha-rides (CPS)] in the subtype of Nostoc sp. that dominates the formation of the biological soil crust. We tested two forms of nitrogen source-N2 and nitrate, and the light intensities at 40 and 80μE/(m2·s). The results showed that the biomass of Nostoc sp. in diazotrophic condition was almost the same to that in non-diazotrophic condition. The production of RPS, CPS and EPS in Nostoc sp. was elevated along with the increase in light intensity in nitrate-grown cultures. How-ever, light intensity did not affect the yields of RPS, CPS and EPS in N2-fixing cultures. Studies in Nostoc sp. metabo-lism showed that the intracellular contents of soluble sugar and sucrose were significantly higher in the presence of ni-trate compared to N2. Interestingly a positive correlation between the sucrose content and RPS/CPS production was only observed at the light intensity of 80μE/m2?s, whereas in the N2-fixing cultures, the total contents of intracellular carbo-hydrate were negatively correlated with CPS production at both tested light intensities. These results suggested that Nostoc sp. had the advantages of utilizing nitrogen and adapting to the light intensity. Although Nostoc sp. in the loga-rithmic phase displays a rapid growth rate, they are able to secrete a considerable amount of EPS which enables them to cement sand grains before forming the spherical hormogonium. Thus, these results further suggested that, during the early stage of the growth of Nostoc sp. in the poor soil surface, the secreted extracellular EPS may originate from the intracellular products of fixing carbon, and sucrose was probably the source for the EPS biosynthesis under high inten-sity of light.