Arsenite toxicity and tolerance in three microalgae, synechococcus leopoliensis, oscillatoria limnetica and Chlorella pyrenoidosa
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Date
1988-12Author
Njoroge, Norman C
Type
ThesisLanguage
enMetadata
Show full item recordAbstract
The cyanobacteria Oscillatoria limnetica and Synechococcus leopoliensis
manifested concentration-dependent growth lags in presence of arsenite above
200pM. There were no detectable growth lags in the Chlorophyte Chlorella
pyrenoidosa in presence of arsenite concentrations above ImM and arsenite
affected the log rate of growth. C. pyrenoidosa was less sensitive to
arsenite than the two cyanobacteria.
Arsenite toxicity in ~ leopoliensis was affected by pH of the medium.
It decreased with an increase in pH. ImM potassium acetate also alleviated
toxicity' in cells grown in presence of 200}lM arsenite. Acetate did not
alleviate toxicity of ~ pyrenoidosa grown in presence of 3mM arsenite.
Cells of the two cyanobacteria grown in presence of 10pM arsenite for up
to 12 hours became tolerant to 200pM arsenite with growth being similar to
that of normal cells. 1.OpM,--arseni te was also adequate to induce arsenite
tolerance but not 0.lpM arsenite. ~l.'re-exposureof C. pyrenoidosa to SOOpM
arsenite for 12 hours indpced some "tolerance" to arsenite concentration of up
to 4mM.
The amounts of arsenic in wnole air-dried tolerant and sensitive cells of
s. leopoliensis,were similar after exposure to 200pM arsenite for 8 or 9
hours. The cyanobacteria accumulated arsenic to about 18-40 times the medium
concentration. The relative amounts of arsenite ~~and arsenate in ice-cold
water extract from tolerant cells were the same as in sensitive cells.
However in recovered cells (after a 30-hour growth lag) almost all arsenic in
the ice-cold water extract was in"form of arsenate. The me cha ni sm of
tolerance in this culture was apparently due to conversion of arsenite to
arsenate. C. pyrenoidosa grown in non-toxic concentration of arsenic (SOOpM)
accumulated a"rsenic to about 80 times the medium concentration after 11 hours.
Possible mechanisms of arsenite tolerance in S. leopoliensis were
investigated. The data did not support a tolerance mechanism based upon
exclusion of arsenite, decreased uptake of arsenite, external or internal
conversion of arsenite to the less toxic arsenate form, (except in recovered
cells), or increase in any identified sulfhydryl compounds. An alternative
pathway for synthesis of acetyl-CoA in which pyruvate dehydrogenase complex is
not involved should be considered.
Citation
MScPublisher
Department of Biology, Queen's University Kingston, Ontario, Canada
Description
Master of Science