دانلود کتاب میکروب‌های قطبی و تغییرات اقلیمی -درک مولکولی برای آینده‌ای پایدار

Oceans cover about 70% of the Earth’s surface and exhibit an average temperature of about 5 °C. Thus, Earth may be considered a rather cold place. The coldest ecosystems on Earth are represented by the Antarctic and Arctic polar regions, which constitute approximately 20% of the Earth’s surface area and account for the annual sequestration of about 32% of the anthropogenic CO2 through carbon capture by the process of photosynthesis. The photosynthetic microorganisms that dominate these cold, polar aquatic habitats include cyanobacteria and green algae that provide an essential ecosystem service for the planet. Many of these polar microorganisms are psychrophiles and thus are adapted to low temperatures. However, since cyanobacteria and algae are photosynthetic, they are considered photopsychrophiles, which represent some of the least studied organisms on Earth. We review the physiological, biochemical, molecular, and genomic adaptations that permit aquatic, polar photopsychrophiles to survive their severe habitats with respect to persistent cold temperatures, low light availability, and extreme photoperiod. These adaptations are discussed first, with respect to the observed biodiversity of polar photopsychrophiles; second, the extent of and the role of gene duplication in the evolution of polar photopsychrophily, and _inally, the mechanisms that govern photosynthetic energy capture and utilization through carbon metabolism, growth, and development. Although the maintenance of energy balance (photostasis) appears to be a critical feature of adaptation of photopsychrophiles to polar environments, the enigma is that there does not appear to be an obvious, single molecular or cellular mechanism that is suf_icient to explain photopsychrophily. Rather, we conclude that evolution in polar environments appears to provide the “possibility space” for the generation of adaptive mechanisms as diverse and varied as the extreme environments in which they have evolved. This fuels a “dynamic persistence” that is the product of natural selection during the evolution of photopsychrophiles in a harsh, thermodynamically challenging polar environment.