Adaptations of Cyanobacteria to High Solar Irradiance: UV Tolerance "Strategies"

该项目的目标是评估紫外线（UV）辐射对蓝藻的光合作用、生长和健康的负面影响，并确定这些微生物在紫外线胁迫下生存的方法。蓝藻（也被称为蓝绿藻）是那些产生氧气的微生物的近亲，这些微生物形成了前寒武纪的叠层石（13 - 30亿年前），并最终导致了地球大气中的高氧值。研究人员提出的问题是，这些微生物使用什么生物“策略”来忍受当前的紫外线压力水平，以及在地球历史上这个严格意义上的微生物时期普遍存在的更高水平的紫外线。他们一直在研究运动细胞的回避反应，以及紫外线“防晒”色素的作用，其中一种色素（细胞催乳素）位于许多物种细胞周围的鞘或胶囊中。研究人员已经能够表征这种黄色色素，并通过实验证明它在允许细胞耐受高紫外线水平方面具有很大的有效性。这种色素提高了蓝藻在其自然栖息地的高太阳辐射下的存活率，并可能为它们在前寒武纪的生长、定植和进化提供了保护。通过了解特定生物体如何保护自己免受这种有害的短波辐射，我们也可以更好地了解其他生物体紫外线损伤的本质。我们正在进行的这类基础研究也可能在人类健康方面得到应用。例如，由于首席研究员以前的工作，现在正在另一个实验室进行临床试验，作为一种具有高效抗炎特性的化合物。在蓝藻的后续研究中，研究人员希望进一步了解在活跃生长和休眠细胞中，丝胞管蛋白在紫外线保护中的作用，以及各种环境因素在丝胞管蛋白合成调节中的作用。此外，研究人员打算确定不具有紫外线筛选色素的蓝藻对紫外线耐受所需的代谢修复过程的程度。在这一系列的实验中，研究人员还将测定由“活性氧”（如单线态氧）引起的细胞损伤程度，这种活性氧也可能由于紫外线吸收而在细胞中产生。如果紫外线的这种次生效应是实质性的，我们将确定细胞类胡萝卜素色素（如β -胡萝卜素）在猝灭这种形式的损害中的作用。

9630674 Castenholz The goals of this project are to evaluate the negative effects of ultra-violet (UV) radiation on photosynthesis, growth, and health of cyanobacteria and to determine the methods used by these microorganisms to survive UV stress. Cyanobacteria (also called blue-green algae) are the closest living relatives of those oxygen-producing microbes that built the Precambrian stromatolites (1 -3 billion yrs ago) and that accounted eventually for the high oxygen values in the Earth's atmosphere. The investigators are asking the question of what biological "strategies" these microorganisms use to tolerate current UV stress levels and the higher levels which would have been prevalent during this strictly microbial period of the Earth's history. They have been working on avoidance responses by motile cells and also on the effect of UV "sunscreen" pigments, one of which (scytonemin), is located in a sheath or capsule surrounding the cells of many species. The investigators have been able to characterize this yellow pigment and experimentally show its great effectiveness in allowing cells to tolerate high UV levels. This pigment enhances survival of cyanobacteria under the high solar radiation of their natural habitats and may have provided the protection for their growth, colonization, and evolution during the Precambrian. By leaming how specific organisms protect themselves from this harmful short-wave radiation, we may also better understand the nature of UV damage in other organisms. Basic research of the type we are doing may lead to applications in human health as well. For example, as a result of previous work by the principal invesigator, scytonemin is now undergoing clinical tests in another laboratory as a compound with highly effective anti-inflammatory properties. In the continuation of this work with cyanobacteria the investig ators hope to further understand the role of scytonemin in UV protection in both actively growing and dormant cells, and the role of various environmental factors in the regulation of scytonemin synthesis. In addition, the investigators intend to determine the extent of metabolic repair processes required for UV tolerance in cyanobacteria that do not possess UV screening pigments. In this line of experimentation the investigators will also assay the degree of damage to cells caused by "reactive oxygen" (e.g. singlet oxygen) which may also be produced in cells as a result of UV absorption. If this secondary effect of UV is substantial, we will determine the role of cell carotenoid pigments (e.g. beta-carotene) in quenching this form of damage.