Microbial Composition of Near-Boiling Silica-Depositing Thermal Springs throughout Yellowstone National Park

The extent of hyperthermophilic microbial diversity associated with siliceous sinter (geyserite) was characterized in seven near-boiling silica-depositing springs throughout Yellowstone National Park using environmental PCR amplification of small-subunit rRNA genes (SSU rDNA), large-subunit rDNA, and the internal transcribed spacer (ITS). We found that Thermocrinis ruber, a member of the order Aquificales, is ubiquitous, an indication that primary production in these springs is driven by hydrogen oxidation. Several other lineages with no known close relatives were identified that branch among the hyperthermophilic bacteria. Although they all branch deep in the bacterial tree, the precise phylogenetic placement of many of these lineages is unresolved at this time. While some springs contained a fair amount of phylogenetic diversity, others did not. Within the same spring, communities in the subaqueous environment were not appreciably different than those in the splash zone at the edge of the pool, although a greater number of phylotypes was found along the pool's edge. Also, microbial community composition appeared to have little correlation with the type of sinter morphology. The number of cell morphotypes identified by fluorescence in situ hybridization and scanning electron microscopy was greater than the number of phylotypes in SSU clone libraries. Despite little variation in Thermocrinis ruber SSU sequences, abundant variation was found in the hypervariable ITS region. The distribution of ITS sequence types appeared to be correlated with distinct morphotypes of Thermocrinis ruber in different pools. Therefore, species- or subspecies-level divergences are present but not detectable in highly conserved SSU sequences.

本研究针对黄石国家公园内7处近沸腾沉积硅质温泉，通过对小亚基核糖体RNA基因（SSU rDNA）、大亚基核糖体DNA及内转录间隔区（ITS）开展环境PCR扩增，解析了与硅华（geyserite）相关的超嗜热微生物多样性分布范围。研究发现，隶属于产液菌目（Aquificales）的红热网菌（Thermocrinis ruber）在所有调查温泉中广泛存在，表明此类温泉的初级生产由氢氧化作用驱动。本研究还鉴定出多个尚无已知近缘类群的进化枝，它们隶属于超嗜热细菌类群。尽管这些进化枝均位于细菌系统发育树的深层分支位置，但当前多数进化枝的精确系统发育定位仍未明确。部分温泉蕴含较为丰富的系统发育多样性，而部分温泉则无此特征。同一温泉内，水下环境与池边溅水区的微生物群落并无显著差异，尽管池边区域的系统型（phylotype）数量更多。此外，微生物群落组成与硅华的形态类型几乎无相关性。通过荧光原位杂交（FISH）与扫描电子显微镜（SEM）鉴定出的细胞形态型数量，多于SSU克隆文库中的系统型数量。尽管红热网菌的SSU序列变异度极低，但在高变ITS区域却存在丰富的序列变异。ITS序列类型的分布似乎与不同温泉池内红热网菌的特有形态型相关。由此可见，物种或亚种水平的分化虽已存在，但在高度保守的SSU序列中无法被检测到。