Bacterioplankton groups involved in the uptake of phosphate and dissolved organic phosphorus in a mesocosm experiment with P-starved Mediterranean waters
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Sebastián M, Pitta P, González JM, Thingstad TF, Gasol JM
Bacteria, phosphate turnover time, oligitrophic, Mediterrranean, Crete, Greece, land-based, 3 m3
The use of inorganic phosphate (Pi) and dissolvedorganic phosphorus (DOP) by different bacterialgroups was studied in experimental mesocosms ofP-starved eastern Mediterranean waters in theabsence (control mesocosms) and presence of additionalPi (P-amended mesocosms). The low Pi turnovertimes in the control mesocosms and theincrease in heterotrophic prokaryotic abundance andproduction upon Pi addition confirmed that the bacterialcommunity was originally P-limited. The bacterioplanktongroups taking up Pi and DOP wereidentified by means of microautoradiography combinedwith catalysed reporter deposition fluorescencein situ hybridization. Incubations with leucinewere also performed for comparative purposes. Allthe probe-identified groups showed a high percentageof cells taking up Pi and DOP in the control,P-limited, mesocosms throughout the experiment.However, in response to Pi addition two contrastingscenarios in Pi use were observed: (i) on day 1 ofthe experiment Pi addition caused a clear reductionin the percentage of SAR11 cells taking up Pi,whereas Gammaproteobacteria, Roseobacter andBacteroidetes showed similar percentages to theones in the control mesocosms and (ii) on day 4 of theexperiment, probably when the bacterial communityhad fully responded to the P input, all the probeidentifiedgroups showed low percentages of cellstaking up the substrate as compared with the controlmesocosms. These differences are likely related todifferent P requirements among the bacterial groupsand point out to the existence of two contrastingstrategies in P use.
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