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Release of Organic Carbon
by Cells of Microcystis aeruginosa (Cyanobacteria)
in Culture under Different Irradiances
BITTAR1,
T.B; COLOMBO1, V. & VIEIRA1, A.A.H.
1
Laboratório de Ficologia - Departamento de Botânica -Universidade
Federal de São Carlos, Via Washington Luís, km 235 – São Carlos – SP
CEP: 13 565-905
thais_bittar@yahoo.com.br
ABSTRACT:
Microcystis aeruginosa is, nowadays, one of the most studied
cyanobacteria due to its potential of toxic bloom formation and
production of great quantities of organic matter in the water column.
Once a bloom is formed, cells of M. aeruginosa, due to the
presence of gas vesicles, can float reaching the water surface, becoming
exposed for long periods to high irradiances. This exposure can injure
the cells, inducing the release of dissolved organic matter (DOM), this harm being even more accentuated with aging
of the cells. The aim of this work was to investigate the effect of
exposure to different irradiances in cells of M. aeruginosa,
isolated from Barra Bonita Reservoir, Tietê River - SP. The relationship
between the photosynthetic rate and light intensities were obtained for
cultures at two ages (8 and 20 days),
using the 14C method. Also, the rates of total fixation and release
(absolute and relative) of carbon, and analysis of
released carbohydrates and molecular weight distribution of DOM as a
function of the irradiances were performed. Carbon fixation by M.
aeruginosa as a function of the irradiances were quantified (as DPM) showing that there was no photoinhibition,
even when the cells were exposed to high irradiances as 2000 mmol m-2s-1.
The rates of DOM released, even in the older culture cells, were
surprisingly low and directly proportional to the photosynthesis rates
in all irradiances tested. Older cells released higher quantities of
high-molecular-weight compounds, including carbohydrates, whereas the
younger ones released low-molecular weight compounds, including
carbohydrates. Chlorophyll-a concentrations indicated a slight
photooxidation or photoaclimatation in the cells at the beginning of the
stationary growth phase of the culture.
Key-words:
Microcystis aeruginosa, irradiance, fixation and release of
carbon, extracellular carbohydrates. |
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