Gleocapsa: Unicellular, Nitrogen Fixer

[Ester]

I've done some browsing on Gleocapsa and found out that it is unicellular. I can find them in wet mounts, ponds, moist soil, damp or wet areas. I also found out that Gleocapsa is a nitrogen fixer.

My question is, since Gleocapsa is surrounded by a clear, gelatinous coating which makes one or more cells clump together within the gelatinous mass, how come we can't consider them multicellular?

My second question is how can we tell that Gleocapsa is a nitrogen fixer? Many sites just say so without any explanation.

 

[Ester]

Does anyone know the answer to the second question?

 

[Moonbear]

I don't know the exact answer, but as with most things in biology, it has probably been experimentally determined in controlled settings. I'm not familiar with how one would test for nitrogen fixation, but I would imagine it would involve in vitro experiments where nitrogen is added to determine what happens to it in these cells.

As for why the would not be considered multicellular, as long as they are just "stuck" together, but don't have specialized structures permitting cell-to-cell signaling (such as gap or tight junctions -- you probably haven't learned about those yet), then they probably are individual organisms living in a colony.

 

[Ouabache]

Does anyone know the answer to the second question?

You could approach this as a biochemist with vessels of nitrogen gas and collect any gases evolved from these organisms in their medium and conduct a chemical anaysis of the medium before and after the experiment.

A less rigid experiment may allow the use of naturally occurring nitrogen in the air.
The fixation reaction for Gloeocapsa takes atmospheric nitrogen and combines with water to produce ammonia and oxygen.
2N2 + 6H2O = 4NH3 + 3O2 ref
The ammonia dissolves in water to form NH4+ (ammonium ion) plus OH- (hydroxyl ion). http://www.fishdoc.co.uk/water/ammonia.htm
If nitrogen is being fixed, the liquid media would become progressively alkaline. (higher pH).
A smell of gaseous ammonia would be another solid clue.

 

[quetzalcoatl9]

testing for reduced nitrogen would be absolute evidence of this.

testing for the presence of enzymes such as FixL would also suggest nitrogen fixing.

not many organisms can fix nitrogen, surprisingly.