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- Fuhrman, J.A., et al.
(författare)
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Diel variations in bacterioplankton, phytoplankton, and related parameters in the Southern California Bight.
- 1985
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Ingår i: Marine Ecology Progress Series. - 0171-8630 .- 1616-1599. ; 27, s. 9-20
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Tidskriftsartikel (refereegranskat)abstract
- The principal objectives of this study were (i) to determine the extent of coupling betweenphytoplankton and microheterotrophs on the shelf off Southern California. (ii) to compare differentmeasures of primary and bacterial secondary production, and (iii) to assess whether sampling timesshould be as strictly controlled for microheterotroph as for autotroph studies. Two diel cycles (May andOctober) were studied by sampling an isotherm as the ship followed paired submerged drogues. Wefound significant die1 changes of chlorophyll, 14C bicarbonate incorporation, bacterial abundance andthymidine incorporation, frequency of dividing bacterial cells (FDC), abundance of non-pigmentedflagellates, particulate organic carbon and nitrogen and their ratios, and dissolved oxygen. Theseparameters all had higher values dunng daylight hours than at night, showing close coupling betweenthe phytoplankton (light-forced) and the microheterotrophs. The ratio of in vivo to extractedchlorophyll a fluorescence, however, displayed a maximum at midnight and minimum at midday,suggesting an endogenous rhythm. Primary production measured by the 14C method was similar to netproduction inferred from in situ oxygen changes. Short-lived peaks in FDC values suggested partlysynchronized bacterial division.
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| 2. |
- Fuhrman, J.A., et al.
(författare)
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Extraction from natural planktonic microorganisms of DNA suitable for molecular biological studies
- 1988
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Ingår i: Applied and Environmental Microbiology. - 0099-2240 .- 1098-5336. ; 54:6, s. 1426-1429
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Tidskriftsartikel (refereegranskat)abstract
- We developed a simple technique for the high-yield extraction of purified DNA from mixed populations ofnatural planktonic marine microbes (primarily bacteria). This is a necessary step for several molecularbiological approaches to the study of microbial communities in nature. The microorganisms from near-shoremarine and brackish water samples, ranging in volume from 8 to 40 liters, were collected on 0.22-,um-pore-sizefluorocarbon-based filters, after prefiltration through glass fiber filters, to remove most of the eucaryotes. DNAwas extracted directly from the filters in 1% sodium dodecyl sulfate that was heated to 95 to 100°C for 1.5 to2 min. This procedure lysed essentially all the bacteria and did not significantly denature the DNA. The DNAwas purified by phenol extraction, and precautions were taken to minimize shearing. Agarose gel electrophoresisshowed that most of the final preparation had a large molecular size (>23 kilobase pairs). The DNA wassufficiently pure to allow complete digestion by the restriction endonuclease Sau3AI and ligation to vector DNA.In a sample in which the extracted DNA was quantified by binding to the dye Hoechst H33258, DNA wasquantitatively extracted, and 45% of the initially extracted DNA was recovered after purification. Final yieldswere a few micrograms of DNA per liter of seawater and were roughly 25 to 50% of the total bacterial DNAin the sample. Alternatives to the initial harvest by filtration method, including continuous-flow centrifugationand thin-channel or hollow-fiber concentration followed by centrifugation, were less efficient than filtration interms of both time and yield, largely because of the difficulty of centrifuging the very small bacteria typical ofmarine plankton. These methods were judged to be less appropriate for studies of natural populations as theyimpose a strong selection for the larger bacteria.
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| 3. |
- Hagström, Åke, et al.
(författare)
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Microbial loop in an oligotrophic pelagic marine ecosystem: Possible roles of cyanobacteria and nanoflagellates in the organic fluxes
- 1988
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Ingår i: Marine Ecology Progress Series. - 0171-8630 .- 1616-1599. ; 49, s. 171-178
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Tidskriftsartikel (refereegranskat)abstract
- In an attempt to quantify the organic fluxes within the microbial loop of oligotrophicMediterranean water, organic pools and production rates were monitored. The production of cyanobacteriaand its dynamics dominated the overall productivity in the system. The largest standing stock wasthat of the bacterioplankton and its growth consumed 8.3 pg C 1-' d-', hence about 60 % of the primaryproduction was required for bacterial growth. Using the MiniCap technique, we measured a predationon bacteria of 2 6 X 104 bacteria ml-' h-'. This was in good agreement with the bacterial production rateof 2.3 X 104 cells rnl-' h-' Thus, growth and predation were balanced for heterotrophic bacterioplankton.Almost all of this predation on bacteria was due to organisms passing a 12 vm Nuclepore filter. Thisraises the question of what mechanisms channel 60 % of primary production into bacteria. We thereforeoutlined a mass-balance model to illustrate routes that could explain this transfer. According to ourmodel the main flux route is cyanobacteria and concomitantly consumed heterotrophic bacteria carboninto bacterivores. A substantial fraction of the bacterivore and the microplankton carbon is released byexcretion and/or cell lysis, to be used by the heterotrophic bacterioplankton. About 86% of theautotrophic production is balanced by respiration due to heterotrophic bacteria and protozoa, leaving6 % of the primary production to higher trophic levels. This scenario should apply to ecosystems wherebacterial production rate is high and comparable to primary production, and the dominant primaryproducers are cyanobacteria. A significant fraction of the photosynthetically fixed carbon will bemineralized within a simple microbial loop, thus rendering it an energy sink in the foodweb.
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