Well if there is a survival advantage to concentrating deuterium, for single cell or complex organisms then by using well known techniques of selection and gene modification, one would suspect that the efficiency could increase exponentially over time. One could cover vast quantities of ocean with a blanket of cellular life which could concentrate Deuterium oxide for very low cost. It could possibly be concentrated as a lipid and used to replace gasoline,
In such a situation we would need to re-evaluate technologies which have been written off before as impractical due to cost. For instance deuterated fuels in an automobile engine with the proper catalyst on the piston crown could possibly create LENR reactions in the flame. No one has tried it because no one thought deuterated fuel could be produced in a renewable low cost way. From: Terry Blanton ➢ There are also many papers dating as far back as 1933 on the biological separation of hydrogen isotopes...not necessarily mycelial, however….It certainly is feasible. Here is a 2016 paper showing the longevity of a particular fungi is increased with the uptake of deuterium oxide. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5515009/