Exopolymer production and microcolony formation by planktonic freshwater bacteria:: defence against protistan grazing
Exopolymer production and microcolony formation by planktonic freshwater bacteria:: defence against protistan grazing
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DOI：
10.3354/ame035297
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发表时间：
2004-05-19
影响因子：
1.4
通讯作者：
Janke, L
中科院分区：
文献类型：
--
作者：
Hahn, MW;Lünsdorf, H;Janke, L
采用分批培养和连续培养的方法，研究了两个新分离的细菌对原生生物取食的防御机制。菌株MWH55和MWH73分离自中营养型湖泊的浮游生物使用的培养条件与强大的鞭毛虫放牧压力。他们的16S rRNA基因的分析表明，这两种菌株属于Betaproteobacteria，并表现出密切的系统发育关系的细菌先前检测到的培养独立的方法在河流生物膜和湖雪聚集。这两种菌株都表现出非常弱的敏感性，鞭毛虫捕食，都形成了嗜热小菌落，超过了鞭毛虫摄入的上限大小，从而保护捕食。这些小菌落由包埋在共同的外聚合物基质中的细胞组成，但相邻细胞之间缺乏直接的细胞与细胞接触。外聚合物基质的小菌落的结构通过电子显微镜观察，而几种荧光标记的凝集素检测胞外多糖失败。基质具有复杂的三维结构，具有应变特异性。目前，尚不清楚这2个分离株是否具有水生生活策略，或者它们是否在固着（生物膜或湖雪聚集体）和水生扩散阶段之间切换。然而，在这两种情况下，低灵敏度的浮游阶段的原生生物捕食是生态上有利的。形成外聚合物基质的能力，使捕食保护的小菌落的形成被认为在这些细菌的生态学中起着关键作用。
The defence mechanisms of 2 novel bacterial isolates against protistan grazing were investigated in experiments with batch and continuous cultures. Strains MWH55 and MWH73 were isolated from the plankton of mesotrophic lakes using culture conditions with strong flagellate grazing pressure. The analysis of their 16S rRNA genes revealed that both strains belong to the Betaproteobacteria and demonstrated a close phylogenetic relatedness to bacteria previously detected by culture-independent methods in river biofilms and lake snow aggregates. Both strains showed a very weak sensitivity to flagellate predation, and both formed planktonic microcolonies that exceeded the upper size limit for ingestion by flagellates, and were thus protected from predation. These microcolonies consisted of cells embedded in a common exopolymeric matrix, yet lacked direct cell-to-cell contact between neighbouring cells. The structure of the exopolymeric matrix of the microcolonies was visualized by electron microscopy, while detection of exopolysaccharides by several fluorescently labeled lectins failed. The matrix possessed a complex 3-dimensional structure with strain-specific characteristics. Currently, it is not clear whether the 2 isolates possess a planktonic life strategy or whether they switch between sessile (biofilm or lake snow aggregates) and planktonic dispersal stages. In both cases, however, a low sensitivity of the planktonic stages to protistan predation is ecologically advantageous. The ability to form an exopolymeric matrix enabling the formation of predation-protected microcolonies is assumed to play a key role in the ecology of these bacteria.