School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand.
Appl Environ Microbiol. 2011 Jul;77(13):4564-72. doi: 10.1128/AEM.02421-10. Epub 2011 May 20.
Protozoa are important components of microbial food webs, but protozoan feeding preferences and their effects in the context of bacterial biofilms are not well understood. The feeding interactions of two contrasting ciliates, the free-swimming filter feeder Tetrahymena sp. and the surface-associated predator Chilodonella sp., were investigated using biofilm-forming bacteria genetically modified to express fluorescent proteins. According to microscopy, both ciliates readily consumed cells from both Pseudomonas costantinii and Serratia plymuthica biofilms. When offered a choice between spatially separated biofilms, each ciliate showed a preference for P. costantinii biofilms. Experiments with bacterial cell extracts indicated that both ciliates used dissolved chemical cues to locate biofilms. Chilodonella sp. evidently used bacterial chemical cues as a basis for preferential feeding decisions, but it was unclear whether Tetrahymena sp. did also. Confocal microscopy of live biofilms revealed that Tetrahymena sp. had a major impact on biofilm morphology, forming holes and channels throughout S. plymuthica biofilms and reducing P. costantinii biofilms to isolated, grazing-resistant microcolonies. Grazing by Chilodonella sp. resulted in the development of less-defined trails through S. plymuthica biofilms and caused P. costantinii biofilms to become homogeneous scatterings of cells. It was not clear whether the observed feeding preferences for spatially separated P. costantinii biofilms over S. plymuthica biofilms resulted in selective targeting of P. costantinii cells in mixed biofilms. Grazing of mixed biofilms resulted in the depletion of both types of bacteria, with Tetrahymena sp. having a larger impact than Chilodonella sp., and effects similar to those seen in grazed single-species biofilms.
原生动物是微生物食物网的重要组成部分，但原生动物的摄食偏好及其在细菌生物膜背景下的影响还不太清楚。本研究使用遗传修饰表达荧光蛋白的细菌生物膜形成菌，研究了两种截然不同的纤毛虫（自由游动滤食者 Tetrahymena sp. 和表面附着捕食者 Chilodonella sp.）的摄食相互作用。根据显微镜观察，两种纤毛虫都很容易消耗 Pseudomonas costantinii 和 Serratia plymuthica 生物膜中的细胞。当在空间上分离的生物膜之间进行选择时，每种纤毛虫都表现出对 P. costantinii 生物膜的偏好。用细菌细胞提取物进行的实验表明，两种纤毛虫都使用溶解的化学线索来定位生物膜。 Chilodonella sp.显然将细菌化学线索用作优先摄食决策的基础，但尚不清楚 Tetrahymena sp. 是否也这样做。活生物膜的共焦显微镜观察显示，Tetrahymena sp.对生物膜形态有重大影响，在 S. plymuthica 生物膜中形成孔和通道，并将 P. costantinii 生物膜减少为孤立的、放牧抗性微菌落。 Chilodonella sp. 的放牧导致 S. plymuthica 生物膜中出现不太明确的轨迹，并使 P. costantinii 生物膜成为细胞的均匀散射。尚不清楚在空间上分离的 P. costantinii 生物膜相对于 S. plymuthica 生物膜的观察到的摄食偏好是否导致对混合生物膜中 P. costantinii 细胞的选择性靶向。混合生物膜的放牧导致两种类型的细菌都耗尽，Tetrahymena sp. 的影响大于 Chilodonella sp.，并且与在放牧的单一物种生物膜中观察到的效果相似。
