School of Biological Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong, SAR, People's Republic of China.
Microb Ecol. 2010 May;59(4):689-99. doi: 10.1007/s00248-009-9607-8. Epub 2009 Nov 25.
The morphology of endolithic colonization in a limestone escarpment and surrounding rocky debris (termed float) at a high-altitude arid site in central Tibet was documented using scanning electron microscopy. Putative lichenized structures and extensive coccoid bacterial colonization were observed. Absolute and relative abundance of rRNA gene signatures using real-time quantitative polymerase chain reaction and phylogenetic analysis of environmental phylotypes were used to characterize community structure across all domains. Escarpment endoliths were dominated by eukaryotic phylotypes suggestive of lichenised associations (a Trebouxia lichen phycobiont and Leptodontidium lichen mycobiont), whereas float endoliths were dominated by bacterial phylotypes, including the cyanobacterium Chroococcidiopsis plus several unidentified beta proteobacteria and crenarchaea. Among a range of abiotic variables tested, ultraviolet (UV) transmittance by rock substrates was the factor best able to explain differences in community structure, with eukaryotic lichen phylotypes more abundant under conditions of greater UV-exposure compared to prokaryotes. Variously pigmented float rocks did not support significantly different communities. Estimates of in situ carbon fixation based upon (14)C radio-labelled bicarbonate uptake indicated endolithic productivity of approximately 2.01 g C/m(2)/year(-1), intermediate between estimates for Antarctic and temperate communities.
采用扫描电子显微镜记录了西藏中部高海拔干旱地区石灰岩峭壁和周围岩石碎片（称为浮石）中的内生菌定殖形态。观察到了疑似地衣化结构和广泛的球菌状细菌定殖。使用实时定量聚合酶链反应和环境基因型的系统发育分析绝对和相对 rRNA 基因特征用于描述所有领域的群落结构。峭壁内生菌主要由真核生物基因型组成，提示与地衣有关的共生关系（一种 Trebouxia 地衣藻共生体和 Leptodontidium 地衣真菌共生体），而浮石内生菌则主要由细菌基因型组成，包括蓝细菌 Chroococcidiopsis 以及几种未鉴定的β变形菌和泉古菌。在所测试的一系列非生物变量中，岩石基质的紫外线（UV）透射率是最能解释群落结构差异的因素，与原核生物相比，真核生物地衣基因型在更多的 UV 暴露条件下更为丰富。不同色素的浮石没有支持明显不同的群落。基于 (14)C 放射性标记的碳酸氢盐摄取的原位碳固定估计表明，内生菌的生产力约为 2.01 g C/m(2)/year(-1)，介于南极和温带群落的估计值之间。
