School of Plant Biology, University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia.
Philos Trans R Soc Lond B Biol Sci. 2013 Jun 10;368(1622):20120264. doi: 10.1098/rstb.2012.0264. Print 2013 Jul 19.
Photolithotrophs are divided between those that use water as their electron donor (Cyanobacteria and the photosynthetic eukaryotes) and those that use a different electron donor (the anoxygenic photolithotrophs, all of them Bacteria). Photolithotrophs with the most reduced genomes have more genes than do the corresponding chemoorganotrophs, and the fastest-growing photolithotrophs have significantly lower specific growth rates than the fastest-growing chemoorganotrophs. Slower growth results from diversion of resources into the photosynthetic apparatus, which accounts for about half of the cell protein. There are inherent dangers in (especially oxygenic) photosynthesis, including the formation of reactive oxygen species (ROS) and blue light sensitivity of the water spitting apparatus. The extent to which photolithotrophs incur greater DNA damage and repair, and faster protein turnover with increased rRNA requirement, needs further investigation. A related source of environmental damage is ultraviolet B (UVB) radiation (280-320 nm), whose flux at the Earth's surface decreased as oxygen (and ozone) increased in the atmosphere. This oxygenation led to the requirements of defence against ROS, and decreasing availability to organisms of combined (non-dinitrogen) nitrogen and ferrous iron, and (indirectly) phosphorus, in the oxygenated biosphere. Differential codon usage in the genome and, especially, the proteome can lead to economies in the use of potentially growth-limiting elements.
光能自养生物分为利用水作为电子供体的生物(蓝细菌和光合真核生物)和利用其他电子供体的生物(非产氧光养生物,均为细菌)。基因组还原程度最高的光能自养生物比相应的化能有机营养生物拥有更多的基因,而生长最快的光能自养生物的比生长速率显著低于生长最快的化能有机营养生物。较慢的生长是由于资源转向光合器官,而光合器官约占细胞蛋白的一半。(特别是含氧)光合作用存在内在危险,包括活性氧(ROS)的形成和水喷溅装置对蓝光的敏感性。需要进一步研究光能自养生物在增加 rRNA 需求的情况下,DNA 损伤和修复以及蛋白质周转率加快的程度。另一个造成环境破坏的相关来源是紫外线 B(UVB)辐射(280-320nm),随着大气中氧气(和臭氧)的增加,地球表面的紫外线 B 辐射通量减少。这种富氧作用导致了对 ROS 的防御要求,以及含氧生物圈中生物对结合(非氮)氮、亚铁和(间接)磷的可用性降低。基因组中尤其是蛋白质组中的差异密码子使用可能导致对潜在生长限制元素的使用更加经济。