The studied bacterial strains grew and evolved hydrogen utilizing orange peel as the sole
carbon and nitrogen source, as much as their respective controls grown in R€AH media only.
Noticeably, orange peel inhibited the uptake hydrogenase (Hup) activity and simultaneously
enhanced the cumulative hydrogen evolution levels. The cumulative hydrogen
was enhanced as hydrogen oxidation/recycling (through the electron transport chain), that
is catalyzed by Hup has been inhibited. Therefore, the role played by orange peel surpassed
its intended role as a source of nutrients. Rather, it seems to act as a specific inhibitor of
Hup activity. Orange peel, in the literature, is famous for its oils and pharmaceutical
components rather than nutritional value. Conversion efficiency of orange peel to
hydrogen was not proportional with its reducing sugars content; it has been inhibited by
high concentrations most probably due to pharmaceutical compounds in orange peel.
The studied strains are purple non-sulfur bacteria (PNS), which have been newly isolated
from local sewage water samples at Assiut and Sohag cities (Upper Egypt). Orange
peel together with PNS, in this respect, is unique. PNS generally cannot use biowastes for
growth, as they do not release exozymes to hydrolyze large molecules (e.g. cellulose, starch
or proteins) into absorbable molecules (sugars, organic acids, amino acids, etc.).
Copyright © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights
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