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Caroline D. Perkins A.Michael Davidson Martin J. Day John C. Fry 《FEMS microbiology ecology》1994,15(1-2):33-44
Abstract The kinetics of conjugation, retrotransfer and mobilisation were studied at 5–15 min intervals between strains of Pseudomonas putida using plasmid pQKH6, isolated from river epilithon, and R300B. Transconjugants from the direct conjugation of pQKH6 and mobilisation of R300B by pQKH6 appeared rapidly, reaching maximum densities within 30–60 min of the start of both filter and liquid mating experiments. However, retrotransconjugants only appeared after a delay. This delay was short (approx. 45–60 min) in filter mating and much longer (2–5 h) for liquid mating experiments. Attempts at predicting the time course of retrotransconjugant development from (1) numbers of transconjugants from the conjugation and mobilisation experiments and (ii) mathematical models based on a mass action approach, both failed to reproduce the observed delay. It was concluded that retrotransfer did not proceed by either a one-step mechanism occuring early in conjugation or two separate conjugation and mobilisation steps. The clear demonstration of a delay in retrotransconjugant formation implies that a new mechanism must be sought. The likely importance of retrotransfer in the environment is discussed. 相似文献
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Kai Piirsoo Sirje Vilbaste Jaak Truu Peeter Pall Tiiu Trei Arvo Tuvikene Malle Viik 《Aquatic Ecology》2007,41(2):183-194
Information on the structure of microalgal assemblages in the epiphyton and epilithon is necessary to understand the origin
of phytoplankton in lowland rivers. To this end, we carried out concurrent investigations on phytoplankton, epiphyton and
epilithon in 18 reaches of three Estonian rivers during the midsummers of 2002 and 2003. A total of 251 taxa was recorded,
of which 192 were epiphyton species, 158 were epilithon species and 150 were phytoplankton species. Canonical correspondence
analysis (CCA), based on the 31 most abundant taxa, indicated differences in the structure of the algal assemblages between
the different biotopes (phytoplankton, epiphyton and epilithon) as well as between the studied rivers. The composition of
the phytoplankton clearly differed from that of the other biotopes, with prevailing small flagellates, a chrysophyte (Synura uvella) and cryptophytes (Rhodomonas lacustris and Cryptomonas erosa). The epiphyton was characterized by a large number of diatoms, while the epilithic community contained filamentous cyanobacteria
(Phormidium tergestinum and Planktolyngya sp.) and a green alga (Stigeoclonium tenue) in addition to diatoms. Based on redundancy analysis (RDA), phosphorous was the most relevant parameter determining the
distribution of species in the phytoplankton assemblages. Shading by trees on the river bank, dissolved oxygen concentration
and water temperature as well as river width determined the distribution of species in the epiphyton. The data set on the
epilithon did not reveal any significant relationships between species distribution and the measured environmental parameters. 相似文献
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The selection and ingestion of epilithic algae byNais elinguis (Oligochaeta: Naididae) 总被引:4,自引:4,他引:0
The gut contents ofNais elinguis in an organically polluted river were dominated by epilithic chlorophycean unicells and pennate diatoms with an average cell volume of 1.3 × 103 µm3. The worm unselectively and opportunistically ingested unicellular algae up to a maximum length of 196 µm and a maximum volume of 24 × 103 µm3, but colonial and filamentous algae were discriminated against. The morphometry of the pharynx ofN. elinguis probably determined the maximum size of algal cells which could be ingested. 相似文献
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