How vitamins auxotrophy has emerged in evolution?

After a long time off, due to my university commitments, I am really pleased to take my fingers back to the keyboard. As you may notice, I did a radical change in my blog template choosing an easier and cleaner one. Hope you like it, I kinda have a spot for minimalism. Today I am going to explore an issue that is both amazing and, in my opinion, too much understated. Even without a biological education, anyone is pretty aware of the importance of vitamins in daily diet. In biochemistry, vitamins are defined as small molecular weight organic compounds that are necessary for survival, but are not synthetized ex- novo. Basically, their role is linked to enzymatic activity, since they often play a co-factor role in catalyzed reactions. In many cases though, these compounds are not required by Protists, Plants, Bacteria and Archea, since they are able to synthesize them ex-novo. The question is how auxotrophy evolved among the different taxa.

My thesis project had an interesting turn as we realized that we could find some clues about the evolution of auxotrophy in B6 vitamins throughout bacteria. The auxotrophy for the pyridoxal- related compounds seems to emerge in all those ecological conditions that may be favorable to those organisms that need external organic compounds, such as commensalism or symbiosis.

Scanning the literature, we can see that Katherine Helliwell, from Cambridge, addressed specifically this issue several times. In a recent paper, Helliwell describes the general mechanisms underlying the loss of biosynthetic pathways for the most common vitamins, highlighting how the evolution of vitamins auxotrophy and the evolution of ecological interactions (predation, mutualism and commensalism) are interlinked.

In another paper, the Cambridge group explains how auxotrophy could have emerged in microalgae. The focus is on B12 vitamin. Citing the author, ‘Within the algal kingdom, approximately half of all microalgal species need the vitamin as a growth supplement, but there is no phylogenetic relationship between these species, suggesting that the auxotrophy arose multiple times through evolution.‘.

Favorable environmental conditions and the loss of at least one of the genes in the biosynthetic pathway, are usually the main reasons for the establishment of auxotrophy. We need vitamins and we know why, but the evolution of this necessity is still to explore.


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