INBIOTEC   24408
INSTITUTO DE INVESTIGACIONES EN BIODIVERSIDAD Y BIOTECNOLOGIA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Promotion of the dominance of filamentous bloom-forming cyanobacteria by environmental factors
Autor/es:
A. ANABELLA; R. ECHENIQUE; G.L. SALERNO; L. AUBRIOT
Lugar:
Mar del Plata
Reunión:
Congreso; X Congreso Argentino de Microbiología General; 2014
Institución organizadora:
Sociedad Argentina de Microbiología General
Resumen:
Raphidiopsis
mediterranea and Planktothrix agardhii are planktonic, filamentous
cyanobacteria belonging to the Nostocales and Oscillatoriales, respectively.
Both are of great concern due to their ability to produce toxins harmful to
humans and animals. In eutrophic freshwater lakes, these two bloom-forming
cyanobacteria occur regularly, but the causes that lead to the dominance of either species are still
unknown. it is not completely known what leads to the
dominance of either species. Studies have pointed out that P. agardhii
is a resilient, shade-tolerant species, favored by turbid conditions with
elevated phosphorus concentrations, while the abundance of R. mediterranea has
been related to less turbid warmer waters.
The
aim of the present work was to investigate the response of P. agardhii and R.
mediterranea to changes in light
and phosphate availability. The approach was done in field and under
controlled laboratory conditions.
A part of the study was
carried out in Los Patos shallow lake, a small eutrophic shallow lake placed in
Buenos Aires province, Argentina (34º 50´ 44´´S, 57º 57´ 26´´W) where dense cyanobacterial blooms performed by both
species have been observed during the past decades. In situ environmental measurements,
nutrient and phytoplankton samples taken were fortnightly
over two years
(April 2012 to April 2014).
In field, although R.
mediterranea and P. agardhii co-occurred and dominated the
phytoplankton during the study, the abundances of the two species were negatively
related: R. mediterranea abundance increased when P. agardhii population
decreased. Regression analyses showed that these species responded differently
to environmental variables such as light and temperature.
The
second approach was carried out at the laboratory, investigating the coexistence
of P. agardhii and R. mediterranea in co-cultures growing in MLA media. Two light intensities
(40 and 80 µmol photon m-2 s-1, low and high
light, respectively) and two phosphate concentrations (5 µM and 10 mM K2HPO4)
were tested in batch cultures over 18 days. The variation in morphology,
abundance and biomass of the two strains growing together were evaluated daily by optical density
(750 nm) and trichome counting by optical microscope.
Before starting the
experiment, the co-culture was dominated by P
agardhii, (83%). After 7 days, there was a shift in the dominances of these
species under high light, which was more pronounced in the of 5 µM treatment.
After 18 days, P. agardhii population
collapsed and the co-culture was dominated completely by R. mediterranea, accounting for the 98% and 96% in the 5 µM and 10
mM treatment, respectively. Under low light, R. mediterranea population increased, but at the end of the
experiment the species co-dominated in both phosphorus conditions. In regards
to the morphology, most of the trichomes of R.
mediteranea counted were straight. A higher proportion of coiled trichomes (approximately
15%) were observed under high light and 10 mM K2HPO4.
These results supported
the conclusion that both species have different environmental preferences. A better
understanding of the environmental conditions that promote the dominance of R. mediterranea or P. agardhii is needed to characterize the niches of these two
bloom-forming species, which will useful to improve water management practices.