Biofilm formation by designed co-cultures of Caldicellulosiruptor species as a means to improve hydrogen productivity

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Background: Caldicellulosiruptor species have gained a reputation as being among the best microorganisms to
produce hydrogen (H2) due to possession of a combination of appropriate features. However, due to their low
volumetric H2 productivities (QH2), Caldicellulosiruptor species cannot be considered for any viable biohydrogen
production process yet. In this study, we evaluate biofilm forming potential of pure and co-cultures of
Caldicellulosiruptor saccharolyticus and Caldicellulosiruptor owensensis in continuously stirred tank reactors (CSTR)
and up-flow anaerobic (UA) reactors. We also evaluate biofilms as a means to retain biomass in the reactor and
its influence on QH2. Moreover, we explore the factors influencing the formation of biofilm.
Results: Co-cultures of C. saccharolyticus and C. owensensis form substantially more biofilm than formed by C.
owensensis alone. Biofilms improved substrate conversion in both of the reactor systems, but improved the QH2
only in the UA reactor. When grown in the presence of each other’s culture supernatant, both C. saccharolyticus
and C. owensensis were positively influenced on their individual growth and H2 production. Unlike the CSTR, UA
reactors allowed retention of C. saccharolyticus and C. owensensis when subjected to very high substrate loading
rates. In the UA reactor, maximum QH2 (approximately 20 mmol · L−1 · h−1) was obtained only with granular sludge
as the carrier material. In the CSTR, stirring negatively affected biofilm formation. Whereas, a clear correlation was
observed between elevated (>40 μM) intracellular levels of the secondary messenger bis-(3′-5′)-cyclic dimeric
guanosine monophosphate (c-di-GMP) and biofilm formation.
Conclusions: In co-cultures C. saccharolyticus fortified the trade of biofilm formation by C. owensensis, which was
mediated by elevated levels of c-di-GMP in C. owensensis. These biofilms were effective in retaining biomass of both
species in the reactor and improving QH2 in a UA reactor using granular sludge as the carrier material. This concept
forms a basis for further optimizing the QH2 at laboratory scale and beyond.


Enheter & grupper

Ämnesklassifikation (UKÄ) – OBLIGATORISK

  • Industriell bioteknik


TidskriftBiotechnology for Biofuels
StatusPublished - 2015
Peer review utfördJa


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