Bacterioplankton groups involved in the uptake of phosphate and dissolved organic phosphorus in a mesocosm experiment with P-starved Mediterranean waters
ABSTRACT The use of inorganic phosphate (Pi) and dissolved organic phosphorus (DOP) by different bacterial groups was studied in experimental mesocosms of P-starved eastern Mediterranean waters in the absence (control mesocosms) and presence of additional Pi (P-amended mesocosms). The low Pi turnover times in the control mesocosms and the increase in heterotrophic prokaryotic abundance and production upon Pi addition confirmed that the bacterial community was originally P-limited. The bacterioplankton groups taking up Pi and DOP were identified by means of microautoradiography combined with catalysed reporter deposition fluorescence in situ hybridization. Incubations with leucine were also performed for comparative purposes. All the probe-identified groups showed a high percentage of cells taking up Pi and DOP in the control, P-limited, mesocosms throughout the experiment. However, in response to Pi addition two contrasting scenarios in Pi use were observed: (i) on day 1 of the experiment Pi addition caused a clear reduction in the percentage of SAR11 cells taking up Pi, whereas Gammaproteobacteria, Roseobacter and Bacteroidetes showed similar percentages to the ones in the control mesocosms and (ii) on day 4 of the experiment, probably when the bacterial community had fully responded to the P input, all the probe-identified groups showed low percentages of cells taking up the substrate as compared with the control mesocosms. These differences are likely related to different P requirements among the bacterial groups and point out to the existence of two contrasting strategies in P use.
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ABSTRACT: The effect of the addition of a limiting nutrient to the composition and structure of bacterial communities in oligotrophic environments remains an interesting question. We conducted a mesocosm experiment to study short-term effects of phosphorus addition on bacterioplankton communities in the Eastern Mediterranean, which is a phosphorus-starved ecosystem. Inorganic phosphorus was added to 10 m deep pelagic water which was transported from offshore Crete, Greece, to mesocosms to yield a final concentration of 100 nM. Using 454 16S amplicon sequencing, we found that phosphorus addition during the first 72 h of the experiment had a minimal effect on bacterioplankton community composition and structure, affecting mostly the abundance of the ‘non-unique’ members of the community.Aquatic Microbial Ecology 07/2014; 72(2). DOI:10.3354/ame01693 · 1.90 Impact Factor
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ABSTRACT: Root phosphatase mediated mineralisation of organic phosphorus (P) can affect P availability in agricultural and forest landscapes. Phosphatases hydrolyse organic P into inorganic P that can be taken up by plants. We developed a method to determine mineralisable organic P by phosphatases exuded by excised live roots/microbial systems. We used excised greenhouse- and field-grown roots with para-nitrophenylphosphate, glucose-1-phosphate and phytic acid as sources of organic P. Experimental variables were analysed including linearity of the reaction, presence of inorganic P, organic P exuded from roots, possible abiotic degradation of organic P, and background inorganic/organic P. Organic P mineralisation by root-phosphatase complexes was found to be linear through 6 h. Phosphorus contaminants into the system were found to be within 10% of mineralised organic P. We used this technique to answer questions about organic P bioavailability, including effect of organic P sources, plant species, plant variety, plant stress and root conditions. Overall, this method was sensitive to organic P source and plant stress of greenhouse and field-grown roots, plant species and root physiological conditions. Unlike other methods used to determine phosphatase activity, this method is not limited by lengthy preparation to develop model plants, nor is there any restriction on the choice of organic P or plant species. Our results suggest that this is an attractive method for determining organic P mineralisation specificity among and within plant species, and it can be easily integrated into routine laboratory analyses.Soil Research 01/2014; 52(2):193. DOI:10.1071/SR13198 · 1.24 Impact Factor
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ABSTRACT: Multiple anthropogenic disturbances to bacterial diversity have been investigated in coastal ecosystems, where temporal variability in bacterioplankton community has been considered as ubiquitous processes. However, far less is known about the temporal dynamics of bacterioplankton community responding to pollution disturbances such as toxic metals. We used coastal water microcosms perturbed with 0, 10, 100, and 1000 μg L(-1) of cadmium (Cd) for two weeks to investigate temporal variability, Cd-induced patterns, and their interaction in coastal bacterioplankton community and to reveal whether bacterial community structure would reflect Cd gradient in temporal varying system. Our results showed that bacterioplankton community structure shifted along the Cd gradient consistently after 4-day incubation, although it exhibited some resistance to Cd at low concentration (10 μg L(-1)). Arm race between temporal variability and Cd exposure was observed, and the temporal variability overwhelmed Cd-induced patterns in bacterial community. Temporal succession of bacterial community was correlated with pH, dissolved oxygen, NO3 (-)-N, NO2 (-)-N, PO4 (3-)-P, dissolved organic carbon, and chlorophyll a, and each of these parameters contributed more to community variance than Cd did. However, elevated Cd levels did decrease the temporal turnover rate of community. Furthermore, key taxa, affiliated to family Flavobacteriaceae, Rhodobacteraceae, Erythrobacteraceae, Piscirickettsiaceae, and Alteromonadaceae, showed high frequency of being associated with Cd level during two weeks. This study provides direct evidence that specific Cd-induced patterns in bacterioplankton community exist in highly varying manipulated coastal system. Future investigations on ecosystem-scale across longer temporal scales are needed to validate the observed pattern.Applied and Environmental Microbiology 10/2014; DOI:10.1128/AEM.02562-14 · 3.95 Impact Factor