I'll try, as much as I understand it (not being a biologist) from my research. Cyanobacteria includes many species, including some that occur in different cell types. One of these, called heterocysts, are specially designed to "fix" nitrogen gas into ammonia, nitrite or nitrates which can then be taken up by plants (aquatic and terrestrial) and converted to proteins nucleic acids; plants cannot biologically take up atmospheric nitrogen.
Cyanobacteria is found in just about all habitats, aquatic and terrestrial. Scientists believe it alone was responsible for converting the original reducing atmosphere of the planet into an oxidating one that led to the formation of algae and life forms beyond that.
Byron.
--- In AquaticLife@yahoogroups.com, SIMMONDS JOHN <simmonds.john@...> wrote:
>
> Thanks Byron,
>
> Very interesting reading, can you explain what you mean by cyanobacteria
> 'fixing' the atmospheric nitrogen please?
>
> John*<o)))<
> *
> On 17 July 2012 15:29, amphibian_ca <bhosking@...> wrote:
>
> > **
> >
> >
> > I carried out a fair degree of research into the question of cleaning or
> > not cleaning the substrate in planted tanks, and I will try to respond to
> > the questions I noted in the threads on this topic.
> >
> > The bacteria responsible for the nitrification process of converting
> > ammonia to nitrite to nitrate are termed nitrifying. But the nitrogen cycle
> > is only complete (in aquaria) when it includes de-nitrification; in this
> > stage, different bacteria that are termed denitrifying convert nitrate into
> > nitrogen gas which is released back into the atmosphere. Another component
> > of the complete nitrogen cycle in nature but not present in our aquaria
> > involves the "fixing" of atmospheric nitrogen by cyanobacteria and other
> > life forms.
> >
> > The denitrifying bacteria are heterotrophic bacteria, of which there are
> > several species; they utilize nitrate by consuming the oxygen within
> > nitrate and releasing nitrogen gas. They do not require free oxygen in the
> > water so they are facultative anaerobes, and generally occur in what we
> > term "dead spots," which occur when water movement is stopped and thus no
> > oxygen is available. These are the good guys among heterotrophs, since
> > de-nitrification is important in a healthy aquarium. And they will
> > naturally occur in the lower level of the substrate as will be explained
> > below.
> >
> > Some species of heterotrophic bacteria break down dead organic matter like
> > fish waste, dead fish or plant matter, uneaten fish food, dead bacteria,
> > etc. Some are aerobic, but many species are facultative anaerobes, able to
> > live with or without oxygen. Like all bacteria, they colonize surfaces [in
> > biofilms], and these are most prevalent in the substrate and the filter
> > media. Many species can survive complete drying, allowing them to remain
> > potent even when filter media that has been previously used is completely
> > dry.
> >
> > These bacteria have only one requirement to appear and live: organics.
> > They compete with autotrophic bacteria for both oxygen and surface area;
> > studies show that even in relatively clean environments, they occupy more
> > than 50% of the available surface area. And given that they can reproduce
> > within 15-60 minutes—compare this to the 12-32 hours required by nitrifying
> > bacteria—you can see how easily these heterotrophic bacteria can overwhelm
> > the system. In a filter, if sludge is allowed to increase, heterotrophic
> > bacteria will multiply so fast they actually smother and kill the
> > autotrophic nitrifying bacteria.
> >
> > The greatest population of bacteria in a healthy balanced aquarium occurs
> > in the substrate, not the filter. The floc or humic compost that collects
> > in the substrate is the host for the biofilms; this is why the substrate in
> > planted tanks should never be disturbed, and many aquarists apply this to
> > non-planted tanks as well.
> >
> > In very general terms, aerobic nitrification takes place in the top 1-2
> > inches of the substrate; anaerobic de-nitrification takes place
> > approximately 2-4 inches down, and anaerobic bacteria producing hydrogen
> > sulfide occurs in substrates deeper than 3-4 inches. In all three cases, it
> > will be deeper in coarse substrates (like pea gravel) and more shallow in
> > finer substrates such as sand. These generalities will also vary with the
> > presence of live plant roots and substrate "diggers" such as snails and
> > worms, since these factors result in more oxygen being made available in
> > the substrate, reducing anaerobic bacteria activity. An oxygen level in the
> > substrate of as little as 1 ppm promotes nitrogen reduction rather than
> > sulfur reduction (hydrogen sulfide). [6]
> >
> > Maintaining a substrate of fine gravel or sand no deeper than 4 inches,
> > having live plants rooted in the substrate, and keeping Malaysian
> > Livebearing snails are the best and safest methods of providing a healthy
> > biological system for aerobic and denitrifying anaerobic bacteria.
> >
> > The above is excerpted from an article I compiled on bacteria in
> > freshwater aquaria, and the source references are included. Those who want
> > to see the sources will find the article here:
> >
> > http://www.tropicalfishkeeping.com/freshwater-articles/bacteria-freshwater-aquarium-74891/
> >
> > Byron.
> >
> >
> >
>
>
> [Non-text portions of this message have been removed]
>
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