I am studying a strange culture of the genus Nostoc (I am quite sure that it is Nostoc by the morphology, ecology, sequencing and phylogeny) which as a natural sample showed branched appearance (yes it did show branched appearance!) but on being grown in the lab in BG11 without nitrogen the branching has been lost. The thing is that we intend to describe it as a new species of Nostoc (it clusters very nicely in the Nostoc sensu stricto clade; quite away from Desmonostoc, Aliinostoc, Mojavia or Halotia) but I suppose the loss of branching is something that needs to be discussed.
Has anyone experienced the same phenomenon?
Dear Prashant, did you observed real branching or polyseriality at some places of the trichome? Can you provide some pictures?
Best regards,
Tomáš
Dear Dr. Singh,
First there is a need to ascertain the nature of branching observed by you in the natural samples; they might have been a case of polyseriality as Dr. Hauer put forward.
To know whether the extra-trichome appendages are truly that and not something else one has to focus on the presence of a septum or pseudo-septum at the point of origin of the so-called branch, always. If affirmative then they are branches or negation means they are anything but.
Now to answer your query, as you have grown the culture in a specific nutrient deficient medium in order to accentuate the nitrogen fixation among the cultured algae, the algae to my opinion have simply responded to that by shedding or forgoing any accessory investment that would be a luxury to them in that environment.
And also to decrease the surface area so that they minimize the effect of the formation of the circumfering zone of nutrient depletion in absence of considerable turbulence. This probably enabled them to sink faster as the consequent shift in the surface area to biovolume ratio rendering the trichomes less buoyant and aids in the fixation of nitrogen through nitrogenase activity even better away from the most oxygenically exposed surface, in spite of specialized cellular chamber to maintain oxygen free environment surrounding nitrogenase.
While in nature none of the limitations were imposed on the trichomes and they could produce branches or similar appendages to increase buoyancy so as to maximize their chances of optimum photosynthesis in a decently or highly turbid productive environment conducive enough to attenuate available PAR. Extra cells on the branches would have allowed for extra chlorophylls to use the circumscribed PAR to the fullest.
With regards,
Dr. Abhishek Mukherjee
Please, send some photos of the branching. It´s very important to be sure how it is. Célia sant´Anna
Hello all:
I am interested in this conversation about true branching in Nostoc, because I see it from time to time. So, according Dr. Mukherjee, facultative branching could occur in Nostoc, and it does not have any taxonomic significance, but it is environmentally induced advantage, correct? I think that there is a paper speculating that branching is response to toxins in the water. Please share your observations an opinion. Thank you!
Hello All,
Great to see this question being brought up again!
As I mentioned in the question itself, the branching was evident clearly in the natural samples and it was lost while sub-culturing in the lab. I think it is more related to the environmental factors, though it has also been induced in the lab too. This particular sample under study was from the Czech Republic.
Branching has been reported previously too by few workers.
We eventually described the isolated cyanobacterium as a new species of Nostoc using a polyphasic approach (so definitely not a new species on the basis of branching!). I attach the published work herein as it does have detailed story.
In our case, we could not attach taxonomic importance to this character simply because it was lost in the lab. Strong and consistent morphological traits should be given weightage in the polyphasic approach but then unique observations like this too can find just a mention appropriately. It will be great if the branching aspect could be studied in detail in Nostoc's. I do not think anyone tried some detailed study with particular focus on this occasional branching.
-PS
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