Diel Buoyancy Changes by the Cyanobacterium Aphanizomenon ovalisporum from a Shallow Reservoir |
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Authors: | Porat Ram; Teltsch Benjamin; Perelman Alex; Dubinsky Zvy |
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Institution: | 1 Mekorot National Water CO. Ltd, Jordan District, Nasin Central Laboratory, Pob 610 Nazareth-Illit 17105 And
2 Department Of Life Sciences, Bar-Ilan University, Ramat-Gan 52100, Israel |
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Abstract: | In the summer of 1999, a bloom (11 100 filaments ml1)of the gas vacuolate cyanobacteriumAphanizomenon ovalisporumdeveloped in a shallow (1.7 m deep) reservoir containing nutrient-enrichedwater from Lake Kinneret (Israel). During 4 days, A. ovalisporumshowed a marked diel periodicity in buoyancy: the proportionof floating filaments fluctuated between 7684% from middayto evening and 9498% at the end of the night, in bothsurface and bottom samples. Buoyant filaments were present throughoutthe water column, presumably due to wind-driven vertical mixing.Aphanizomenonfilaments collected from the reservoir were maintained undermean photon irradiances of 15 (LL), 150 (ML) and 1100 (HL) µmolm2 s1 in a computer-controlled set-up, which simulatedthe diel light changes at different depths in the reservoir.In the LL cultures, filament buoyancy showed no diel fluctuationpatterns during the 4 days of incubation, but ML and HL culturesshowed regular diel changes, with a higher proportion of filamentsfloating at the end of the night than during middayevening.There was no evidence for either turgor-driven collapse of gasvesicles or dilution of gas vesicles by cell growth by any ofthe treatments. Gas vesicles of A. ovalisporum had a relativelylow mean critical pressure (pc of 0.57 MPa), but the daytimerise in turgor pressure was too small to cause gas vesicle collapse.The observed diel buoyancy changes may be explained by accumulationof carbohydrate ballast during the day and decrease during thenight. |
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