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footloose nitrifiers

> >Karen wrote:
> >
> >> Nitrifying bacteria colonize substrates.  They are not free floating.
> Cynthia wrote:
> >AFAIK this is incorrect.   Nitrifiying bacteria are ubiquitous in aquaria;
> >on the substrate, ornaments, plants and in the water.
> I don't believe this is correct.  Ornaments and plants _are_ substrates for
> nitrifying bacteria.  Someone correct me if I'm wrong, but my understanding
> is that they are _not_ free floating in the water column.

I was about to respond to Cynthia much as Karen did, then stopped and
reread my source on nitrifying and nitratifying bacteria (which I don't
have on hand as I write this).  What it said was that nitrifying and
nitratifying bacteria are motile - they can be and sometimes are free
swimming.  But our filters, the larger-scale biofilters used in
aquaculture and even the *really* large scale reactors used in municipal
and industrial water treatment systems depend on the bacteria adhering to
surfaces, which they often do.

The authors believe that the nitrifying bacteria attach themselves to a
substrate when they are stressed by predatory interaction or by low
availability of ammonia and nitrite.  They claim those conditions normally
prevail in bioreactors.

So in a sense, both Cynthia and Karen are right.  The nitrifying and
nitratifying bacteria can be free swimming and under some conditions will
be free swimming, but under aquarium conditions they normally live
attached to surfaces.

Roger Miller