Does anybody have a reliable method of being able to measure increased microbial biomass during a ready biodegradation test (e.g. OECD 301F) between the beginning and the end of the test (or even at intermediate times if the method is not destructive of the entire rep)? Measurement of TOC is not a solution. How do we discriminate living biomass from TOC?
I would measure suspended solids. Biomass is retained by a 0.45 filter, dissolved test substance isn't. If you are using TOC you might separate the biomass by centrifugation so you measure TOC in the sample with and without centrifugation.
If you need something nondestructive, it could be optical density (absorbance at e.g. 600 nm assuming your test substance isn't colored) or turbidity.
Thanks Henrik, but I wasn't referring to test substance when I mentioned TOC, I was referring to non-living organic and inorganic carbon which we need to separate out from living cells.
Any other thoughts?
Thanks
It would seem this non-dissolved, non-living biomass would not change during the experiment so you can find the biomass as the difference in filterable TOC from the beginning of the test.
If not, perhaps you can explain what the matter you refer to is?
Well that's what I thought too, but in fact the microorganisms seem to be using the available OM which comes in with the inoculum in their nutriment cycle process. So for a readily biodegradable mixture we didn't find any real change in TOC of the filterable suspended solids between beginning and end of the 28 d experiment. And I strongly suspect that in reality pretty much all the TS was mineralised so the TS was not itself transformed to biomass in thsi case, but biomass increased and came from the non-living OM that was present at the start of the study, and that's why I want to have a good method to differentiate living OM for non-living.
Paul Christopher Thomas ; I don't remember the test details, but it seems that if your inoculum was smaller you could better control the experiment.
Generally the biomass yield of easily degradable substrates without mineral limitations (N,P) is almost 50 % so your TS should make some biomass.
Henrik Rasmus Andersen I was indeed surprised that there was not a more evident increase in biomass yield after 28 d in the experiments too. It's a 301F so we're a bit limited in the amount we can reduce the inoculum. We could try reducing the inoculum a bit and see what happens. Thanks for your help. If you know of any other way to differentiate living from non-living OC then please let me know.
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