Arana I, Irizar A, Seco C, Muela A, Fernández-Astorga A, Barcina I
Faculdad de Ciencias, Departamento de Inmunología, Microbiología y Parasitología, Universidad del País Vasco, Apdo. 644, E-48080 Bilbao, Spain.
Microb Ecol. 2003 Jan;45(1):29-38. doi: 10.1007/s00248-002-1029-9. Epub 2002 Nov 27.
We have used an Escherichia coli strain DH5a containing pGreenTIR to study the survival of this bacterium in river water. As green fluorescence was maintained throughout survival both in dark and illuminated conditions, gfp-tagged E. coli cells were clearly distinguished from the microbial community of the river Butrón. gfp-tagged E. coli cells were monitored to estimate total density as well as the density of the culturable and viable (active electron transport system, CTC+) cells. Our results indicate that autochthonous bacteria and introduced E. coli are predated by flagellates. The autochthonous bacterial community behaves as predation-escaping prey, showing a tendency to cellular miniaturization and so maintaining the density of the population. In contrast, introduced E. coli behaves as predation-non-escaping prey, so E. coli was eliminated from the system. When comparing the elimination by predation of heat-treated and non-heated gfp-tagged E. coli cells we deduce that the flagellates do not discriminate between live and heat-treated cells. Finally, in the presence of the river microbial community, the E. coli cells appeared to be ingested before cellular deterioration could occur. Thus predation reduces the quantitative importance of the viable but nonculturable (VBNC) population of E. coli in the aquatic systems.
我们使用了含有pGreenTIR的大肠杆菌菌株DH5a来研究这种细菌在河水中的存活情况。由于在黑暗和光照条件下存活过程中绿色荧光一直保持，带有绿色荧光蛋白（gfp）标签的大肠杆菌细胞能够与布特罗河的微生物群落清晰区分开来。对带有gfp标签的大肠杆菌细胞进行监测，以估计其总密度以及可培养和有活力（具有活性电子传递系统，CTC+）细胞的密度。我们的结果表明，本地细菌和引入的大肠杆菌会被鞭毛虫捕食。本地细菌群落表现为逃避捕食的猎物，呈现出细胞小型化的趋势，从而维持种群密度。相比之下，引入的大肠杆菌表现为不逃避捕食的猎物，因此从系统中被消除。当比较经热处理和未经热处理的带有gfp标签的大肠杆菌细胞被捕食的消除情况时，我们推断鞭毛虫不会区分活细胞和热处理过的细胞。最后，在存在河流微生物群落的情况下，大肠杆菌细胞似乎在细胞恶化发生之前就被摄取了。因此，捕食降低了水生系统中大肠杆菌活的但不可培养（VBNC）种群的数量重要性。
