Uppsala Universitet
Evolutionsbiologiskt Centrum
Avdelningen för Limnologi
Bacterial growth efficiency on different concentrations of
natural dissolved organic matter
by Alexander Eiler
Abstract
Batch cultures of natural bacterial assemblages and lake water dissolved organic matter were used to
examine the impact of carbon source concentration on bacterial growth, cell volume, the maximal
bacterial biomass, the bacterial growth and the bacterial growth efficiency. An aged concentrate of
dissolved organic matter from a humic lake was diluted with artifical organic-free lake water
containing excess inorganic nutrients to achieve a range of concentrations from 0.5 to 30 mg dissolved
organic carbon (DOC) per liter.
The volume of cells developing in the cultures was independent of DOC concentration, except at the
lowest DOC concentration, where cells were smaller. Bacterial biomass produced in the cultures
increased linearly with DOC concentration, indicating that the maximal bacterial biomass was limited
by the supply of carbon. However, the bacterial growth rate (BGR) during exponential phase exhibited
a hyperbolic response to increasing DOC concentration, which suggests that the maximal attainable
growth rate was increasingly constrained with decreasing concentration of substrate.
The bacterial growth efficiency (BGE), which was calculated from increments in biomass and the CO 2
production or the DOC decrease, ranged from 0.4 % to 8 %. BGE increased exponentially with
increasing DOC concentration, and it increased with increasing BGR until reaching a plateau. Hence,
it is only at low concentrations of DOC that BGE may be limited by the substrate supply. In
environments where the concentration of DOC is high, variations in BGE may be due variability in the
quality, rather than the quantity of substrate.
Master Thesis in Biology
Examensarbete i biologi, 20p
Evolutionary biology centre
Department of Limnology
Supervisor: Lars Tranvik
Scripta
Limnologica
Upsaliensia
2002 B:7