title: Exploitation of algal-bacterial associations in a two-stage biohydrogen and biogas generation process.
abstract: BACKGROUND
  The growing concern regarding the use of agricultural land for the production of biomass for food/feed or energy is dictating the search for alternative biomass sources. Photosynthetic microorganisms grown on marginal or deserted land present a promising alternative to the cultivation of energy plants and thereby may dampen the 'food or fuel' dispute. Microalgae offer diverse utilization routes.
  
  
  RESULTS
  A two-stage energetic utilization, using a natural mixed population of algae (Chlamydomonas sp. and Scenedesmus sp.) and mutualistic bacteria (primarily Rhizobium sp.), was tested for coupled biohydrogen and biogas production. The microalgal-bacterial biomass generated hydrogen without sulfur deprivation. Algal hydrogen production in the mixed population started earlier but lasted for a shorter period relative to the benchmark approach. The residual biomass after hydrogen production was used for biogas generation and was compared with the biogas production from maize silage. The gas evolved from the microbial biomass was enriched in methane, but the specific gas production was lower than that of maize silage. Sustainable biogas production from the microbial biomass proceeded without noticeable difficulties in continuously stirred fed-batch laboratory-size reactors for an extended period of time. Co-fermentation of the microbial biomass and maize silage improved the biogas production: The metagenomic results indicated that pronounced changes took place in the domain Bacteria, primarily due to the introduction of a considerable bacterial biomass into the system with the substrate; this effect was partially compensated in the case of co-fermentation. The bacteria living in syntrophy with the algae apparently persisted in the anaerobic reactor and predominated in the bacterial population. The Archaea community remained virtually unaffected by the changes in the substrate biomass composition.
  
  
  CONCLUSIONS
  Through elimination of cost- and labor-demanding sulfur deprivation, sustainable biohydrogen production can be carried out by using microalgae and their mutualistic bacterial partners. The beneficial effect of the mutualistic mixed bacteria in O2 quenching is that the spent algal-bacterial biomass can be further exploited for biogas production. Anaerobic fermentation of the microbial biomass depends on the composition of the biogas-producing microbial community. Co-fermentation of the mixed microbial biomass with maize silage improved the biogas productivity.
authors: Department of Biotechnology, University of Szeged, Közép fasor 52, H-6726 Szeged, Hungary.
authors: Roland
authors: R
authors: Wirth
authors: Institute of Biochemistry, Biological Research Center, Hungarian Academy of Sciences, Temesvári krt. 62, H-6726 Szeged, Hungary.
authors: Gergely
authors: G
authors: Lakatos
authors: Institute of Biochemistry, Biological Research Center, Hungarian Academy of Sciences, Temesvári krt. 62, H-6726 Szeged, Hungary.
authors: Gergely
authors: G
authors: Maróti
authors: Department of Biotechnology, University of Szeged, Közép fasor 52, H-6726 Szeged, Hungary.
authors: Zoltán
authors: Z
authors: Bagi
authors: Department of Oral Biology and Experimental Dental Research, University of Szeged, Tisza L. krt. 64, 6720 Szeged, Hungary.
authors: János
authors: J
authors: Minárovics
authors: Department of Oral Biology and Experimental Dental Research, University of Szeged, Tisza L. krt. 64, 6720 Szeged, Hungary.
authors: Katalin
authors: K
authors: Nagy
authors: Institute of Biochemistry, Biological Research Center, Hungarian Academy of Sciences, Temesvári krt. 62, H-6726 Szeged, Hungary.
authors: Éva
authors: É
authors: Kondorosi
authors: Department of Biotechnology, University of Szeged, Közép fasor 52, H-6726 Szeged, Hungary.|Institute of Biophysics, Biological Research Center, Hungarian Academy of Sciences, Temesvári krt. 62, H-6726 Szeged, Hungary.
authors: Gábor
authors: G
authors: Rákhely
authors: Department of Biotechnology, University of Szeged, Közép fasor 52, H-6726 Szeged, Hungary.|Institute of Biophysics, Biological Research Center, Hungarian Academy of Sciences, Temesvári krt. 62, H-6726 Szeged, Hungary.|Department of Oral Biology and Experimental Dental Research, University of Szeged, Tisza L. krt. 64, 6720 Szeged, Hungary.
authors: Kornél L
authors: KL
authors: Kovács
keywords: Algal bacterial co-culture; Biogas; Biohydrogen; Metagenomics; Microalgae