Thank you Sandipan.

It's a nice explanation. I'm so convinced.

Best regards

Attached an image of dried salted agar

I agree with Sandeepan. We often see this with dried agar plates. they are salt crystals in the media which take up this filamentous structures on drying.

Thanks a lot Padmapriya and Abdelraouf

You're right. It's logical.

Bests regards

O yes, this is due to dryness under low temperature, medium components (salts) appear like that if plates are placed for longer time period in fridge.

Some bacteria can produce struvite crystals (NH4MgPO4 • 6H2O) in agar with different morphologies (prismatic, platy, raphidic etc.). It is still a phenomenon due to dehydration and media saturation with some salts, but also some abilities of the bacteria in concentrating biogenic compounds or acting as nucleation sites can have a role. In the case of struvite, bacterial production has been reported as the consequence of the combination of ammonium ions produced by the metabolism of nitrogenous compound with phosphate and Mg present in the growth environment. See papers by Sánchez-Román and Rivadeneyra, M (i.e. FEMS Microbiology Ecology, v. 61, p. 273–284). The picture you posted is not clear, but the minerals are not dendritic, they look more localised in the colony.

All the best,

Flavia

Really interesting explanation, Flavia. I'll read papers. Thanks a lot.

I too had always found crystals formed in agar media in petri plates or broth in conical flasks after prolonged incubation at room temperature as well as in the refrigerator. However I had also read articles on morphological variations in bacterial colony formation with different media, temperature and other environmental conditions. So it would fine to check all possible reasons to come to a conclusion.

Yes during prolong incubation salt crystals are formed.