For each combination of organisms, 8 parallel chemostats were arranged along a gradient of increasing glucose concentration in the reservoirs. Glucose and/or orthophosphate were the limiting nutrients.
(Glucose is for a carbon source.)
In cultures with bacteria alone, exhaustion of the medium for both glucose and phosphate was observed for an extended range of reservoir C:P ratios, in a sense violating ‘Liebigs law of the minimum’.
In cultures with bacteria and flagellates, glucose degradation was stimulated relative to the cultures with bacteria alone, an effect attributed to phosphate remineralization. In these cultures, an increase in reservoir glucose concentration led to increased numbers of bacterial predators, not to increased numbers of bacteria.
It’s interesting to consider the downstream effects like this.
In cultures with bacteria and algae, the bacteria outcompeted algae for phosphate, and algae disappeared from the cultures at high reservoir C:P ratios.
Bacteria vs algae is the magic scenario we hope for when we carbon dose our tanks – that bacteria will “automagically” make the algae go away. We see here that in some cases it does work out. But as we see next, a “balanced system” promotes all three lifeforms.
In mixed cultures with all 3 trophic levels, bacterial degradation of glucose was strongly impeded relative to all the other situations with bacteria present. Consequently, only a minor effect of glucose degradation on ecosystem composition could be discerned. In these 3-species communities, algae maintained themselves in the cultures at all reservoir glucose concentrations. These effects were attributed to the combined pressure of predation and competition on the bacteria, and could not be explained by any of these mechanisms individually.
Just interesting to see how this worked out!
The rest of the article is worth reading too.
Last, just so you know, JSTOR is worth subscribing to even as a hobbyist as you get free access to any 3 docs at once from their library.