Cho Jang-Cheon, Giovannoni Stephen J
Department of Microbiology, Oregon State University, Corvallis, Oregon 97331, USA.
Appl Environ Microbiol. 2004 Jan;70(1):432-40. doi: 10.1128/AEM.70.1.432-440.2004.
Forty-four novel strains of Gammaproteobacteria were cultivated from coastal and pelagic regions of the Pacific Ocean using high-throughput culturing methods that rely on dilution to extinction in very low nutrient media. Phylogenetic analysis showed that the isolates fell into five rRNA clades, all of which contained rRNA gene sequences reported previously from seawater environmental gene clone libraries (SAR92, OM60, OM182, BD1-7, and KI89A). Bootstrap analyses of phylogenetic reliability did not support collapsing these five clades into a single clade, and they were therefore named the oligotrophic marine Gammaproteobacteria (OMG) group. Twelve cultures chosen to represent the five clades were successively purified in liquid culture, and their growth characteristics were determined at different temperatures and dissolved organic carbon concentrations. The isolates in the OMG group were physiologically diverse heterotrophs, and their physiological properties generally followed their phylogenetic relationships. None of the isolates in the OMG group formed colonies on low- or high-nutrient agar upon their first isolation from seawater, while 7 of 12 isolates that were propagated for laboratory testing eventually produced colonies on 1/10 R2A agar. The isolates grew relatively slowly in natural seawater media (1.23 to 2.63 day(-1)), and none of them grew in high-nutrient media (>351 mg of C liter(-1)). The isolates were psychro- to mesophilic and obligately oligotrophic; many of them were of ultramicrobial size (<0.1 micro m(3)). This cultivation study revealed that sporadically detected Gammaproteobacteria gene clones from seawater are part of a phylogenetically diverse constellation of organisms mainly composed of oligotrophic and ultramicrobial lineages that are culturable under specific cultivation conditions.
利用高通量培养方法，从太平洋沿海和远洋区域培养出44株新型γ-变形菌，该方法依赖于在极低营养培养基中进行稀释至灭绝培养。系统发育分析表明，分离出的菌株分为5个rRNA进化枝，所有进化枝均包含先前从海水环境基因克隆文库中报道的rRNA基因序列（SAR92、OM60、OM182、BD1-7和KI89A）。系统发育可靠性的自展分析不支持将这5个进化枝合并为一个进化枝，因此将它们命名为贫营养海洋γ-变形菌（OMG）组。选择代表这5个进化枝的12个培养物在液体培养中连续纯化，并测定它们在不同温度和溶解有机碳浓度下的生长特性。OMG组中的分离物是生理特性多样的异养菌，它们的生理特性通常遵循其系统发育关系。OMG组中的分离物在首次从海水中分离时，在低营养或高营养琼脂上均未形成菌落，而在实验室测试中传代培养的12个分离物中有7个最终在1/10 R2A琼脂上形成了菌落。分离物在天然海水培养基中生长相对缓慢（1.23至2.63天-1），且没有一个在高营养培养基（>351毫克碳/升）中生长。分离物为嗜冷至嗜温菌，且专性贫营养；其中许多为超微尺寸（<0.1微米3）。这项培养研究表明，从海水中偶尔检测到的γ-变形菌基因克隆是一个系统发育多样的生物群体的一部分，该群体主要由贫营养和超微生物谱系组成，在特定培养条件下可培养。
