Gp. Genoni et al., Complex dynamics of adaptation in a nonaxenic Microcystis culture - 1. Effects of dinitrophenol on population growth, ECOTOX ENV, 48(3), 2001, pp. 235-240
Chronic exposure to toxicants is a selective pressure affecting populations
and also the interactions between populations. Nonaxenic cultures of the b
lue-green alga Microcystis aeruginosa were used to investigate the ecologic
al dynamics and the effect of preexposure to 2,4-dinitrophenol (DNP) on the
tolerance toward subsequent DNP inputs. It was predicted that preexposure
would induce an increased tolerance to further inputs. This should cause a
higher population growth rate under a given DNP exposure, a broader toleran
ce range (the range of concentrations over which population growth can be s
ustained), a higher EC50 and a lesser variability in growth rates, over the
range of experimental exposure concentrations. DNP reduced Microcystis gro
wth proportionally to exposure concentration, Light, inorganic carbon, and
DNP were likely limiting factors for algal growth. Heterotrophic bacteria p
resumably used the dead cells and the exudate of living algae as substrates
, Some unexpected effects occurred, such as an apparent increase in dissolv
ed DNP in the medium following its initial decline and fluctuations of the
bacterial population. The hypotheses were verified as concerns the effect o
f preexposure on tolerance. Changes were apparent in the EC50 and in the br
eadth of the tolerance range, Moreover, the variability of preexposed popul
ations, in terms of algal growth rate, over the range of exposure concentra
tions, was smaller than that of non-preexposed populations. Such a decrease
in variability may reduce the potential of a population to resist further
stresses, (C) 2001 Academic Press.