témavezető: Maróti Gergely
helyszín (magyar oldal): Institute of Biochemistry, HAS BRC helyszín rövidítés: SzBK
A kutatási téma leírása:
Project Summary
Green algae have exceptional metabolic potential, and their exploitation possibilities are highly diverse (food industry, biomass-based energy generation, wastewater treatment, etc.). Green algae thrive in nature in complex communities, even the axenic laboratory cultivation and maintenance represent special challanges. The planned PhD project aims the investigation of various algal-bacterial communities with an emphasis on the algal biohydrogen production. High-throughput genomic approaches will be used to reveal the metabolic background of algal-bacterial interactions, the effects of natural and artificial bacterial partners on the biohydrogen production of Chlamydomonas, Scenedesmus and Chlorella algae will be investigated. The level of interspecies interactions will be analyzed using transcriptomic, metatranscriptomic approaches, while analytical measurements will be performed to identify metabolites playing roles in the development and maintenance of symbiotic functions.
Background
The vast majority of algal hydrogen evolution studies were conducted using pure algae cultures, although algae almost exclusively live in complex ecosystems in nature where they interact with multiple micro- and macroorganisms. The algal FeFe hydrogenases can be activated under proper environmental conditions in certain Chlamydomonas, Scenedesmus and Chlorella species. The FeFe hydrogenases can convert the light energy into biohydrogen with 10 % efficiency. However, they are highly sensitive for the presence of oxygen, which inhibits the continuous photolytic hydrogen production. The indirect photolysis can solve this problem by dissecting the hydrogen evolution and oxygen production phases. First, the energy of the illumination is stored in starch, then the starch is degraded and utilized. Thus, hydrogen evolution is separated from the photosynthetic oxygen production temporally. The most prevalent method of algal indirect photolytic hydrogen productionis based on sulfur deprivation of the culture medium. During sulfur deprivation, the algae cells first accumulate carbohydrates and nutrients, then they start degrading their protein stores to survive the nutrient stress. It causes major reduction in the number of the active D1 proteins of the II. photochemical system (PSII), which finally inhibits further oxygen production of the algae cells. The reduced oxygen evolution and the active cell respiration allow the closed system to become anaerobic, thus enhancing the activation of hydrogenases. The major disadvantage of this method is that the algae cultures must be grown up first, then the original medium must be changed to a sulfur-free medium. This process definitely requires extra time, material and energy, which makes the starting of the industrial application more difficult. The hydrogen production process is an approximately five day-long period. The term of hydrogen evolution can be prolonged by the re-addition of sulfur for a few weeks, but it causes the reduction of the hydrogen production efficiency. The oxygen consumption period takes at least one day, which also reduces the industrial feasibility of the hydrogen production. Besides, the living cell number is continuously decreasing because of the nutritional stress effect.
Current Research
The green alga Chlamydomonas sp. 549 was shown to readily associate with various bacterial species during cultivation. A number of natural bacterial partners were separated and identified, most belonging to Rhodococcus, Brevundimonas, and Leifstonia genera. Each combination was characterized for growth and biomass-yield properties. Rhodococcus partners were shown to be the most abundant and most rapidly growing bacterial participants in the associations. Therefore, this association produced the most hydrogen among the natural combinations. Aside from natural partners, various further bacterial strains were able to efficiently reduce the oxygen level and further enhance hydrogen production. Use of the E. coli pleiotropic hydrogenase mutant strain hypF resulted in the generation of the largest hydrogen amount. The hydrogen evolution characteristics of Chlamydomonas sp. 549 were compared to those of the widely used green alga C. reinhardtii cc124. Comparisons were made with pure algae and mixed algal-bacterial cultures using either full medium (TAP) or the sulfur-deprived method, which is the benchmark method for algae-based hydrogen evolution. Striking differences were observed between the various algae strains in terms of oxygen consumption intensity, starting time, and duration of hydrogen evolution. The complete anaerobiosis in sulfur-deprived pure C. reinhardtii cc124 cultures was established in 96 h under illumination, while the algal-bacterial cultures—either with or without sulfur deprivation—generated fully anaerobic environments in 24 h as measured in the headspace of the bottles.
Fluorescence investigations were used to examine the state of the photosynthetic system in algae during the experiments under illumination. A highly reduced PQ pool was observed in the mixed cultures. Thus, algal PSII remained intact and fully active with respect to hydrogen production by algal-bacterial cultures in contrast to the decreased PSII activity observed in sulfur-deprived ones.
Specific aims
1. Investigation of the hydrogen production of mixed algal-bacterial and axenic algal cultures in dark and under illumination, combined application of the described hydrogen production methods.
2. Analysis of the algal photosynthetic system, investigation of the hydrogen metabolism and connected metabolic pathways of the model algae.
3. Molecular investigation of the algal-bacterial interaction (combined genomic, transcriptomic and analytical approaches).
Methods to be used
Cultivation of algae and bacteria
Analytical measurements, gas chromatography
Investigation of the photosynthetic system
Molecular biology techniques (DNA manipualtion, protein analysis, purification, NGS-based transcriptome analysis, etc.)
Suggested literature
Beer L. L. et al. Engineering algae for biohydrogen and biofuel production. Curr. Op. Biotech. 20, 264-271. (2009).
Doebbe A. et al. The interplay of proton, electron, and metabolite supply for photosynthetic H2 production in Ch. reinhardtii. J. Biol.Chem. 285, 30247-30260. (2010).
Forestier M. et al. Expression of two [Fe]‐hydrogenases in Ch. reinhardtii under anaerobic conditions. European J. Biochem. 270, 2750-2758. (2003).
Ghirardi M. L. et al. Hydrogenases and Hydrogen Photoproduction in Oxygenic Photosynthetic Organisms. Annu. Rev. Plant Biol., 58, 71-91. (2007).
Happe T. et al. Biological activation of hydrogen. Nature, 385, 126-126. (1997).
Kovács K. L. et al. A novel approach for biohydrogen production. Int. J. Hydrogen Energy, 31, 1460-1468. (2006).
Kruse O. et al. Improved photobiological H2 production in engineered green algal cells. J. Biol.Chem.280, 34170-34177. (2005).
Melis A. Photosynthetic H2 metabolism in Ch. reinhardtii (unicellular green algae). Planta, 226, 1075-1086. (2007).
Posewitz M. C. et al. Discovery of two novel radical S-adenosylmethionine proteins required for the assembly of an active [Fe] hydrogenase. J. Biol. Chem. 279, 25711-25720. (2004).
Winkler M. et al. Isolation and molecular characterization of the [Fe]-hydrogenase from the unicellular green alga Chlorella fusca. BBA-Gene Structure and Expression, 1576, 330-334. (2002).
Wu S. et al. Increased hydrogen production in co-culture of Ch. reinhardtii and Bradyrhizobium japonicum. Biores.Tech. 123, 184-188. (2012).
SNAPSHOT OF THE HOST LABORATORY
Selected publications
Boboescu I. Z. et al. Revealing the factors influencing a fermentative biohydrogen production process using industrial wastewater as fermentation substrate. Biotech. Biofuels, 7:139, doi: 10.1186/s13068-014-0139-1. (2014)
Lakatos G. et al. Bacterial symbionts enhance photo-fermentative hydrogen evolution of Chlamydomonas algae. Green Chemistry 16 (11), 4716 - 4727. (2014)
Maróti G. and Kondorosi É. Nitrogen-fixing Rhizobium-legume symbiosis: Are polyploidy and host peptide-governed symbiont differentiation general principles of endosymbiosis? Front. Microbiol. doi: 10.3389/fmicb.2014.00326. (2014)
Farkas A. et al. The Medicago truncatula symbiotic peptide NCR247 contributes to bacteroid differentiation through multiple mechanisms. PNAS 111:5183-88. (2014)
Pap B. et al. Temperature-dependent transformation of biogas-producing microbial communities points to the increased importance of hydrogenotrophic methanogenesis under thermophilic operation. Biores. Technol. doi: 10.1016/j.biortech.2014.11.021. (2014)
Selected grants
SYMBIOTICS (ERC Advanced Grant to Éva Kondorosi), ERC (EU), 2011-2016
ALGOLABH: Development of an algae-based hydrogen producing system, NKTH (Hungary), 2010-2013
BIOSIM: Simultaneous biohydrogen production and wastewater treatment by selectively enriched anaerobic mixed microbial consortium, UEFISCDI (Romania), 2012-2015
Gergely Lakatos, PhD student, 2011-2015, Algal-bacterial communities for biohydrogen production
Ildikó Nagy, PhD student, 2011- Fuction and regulation of hydrogenase enzymes in photosynthetic bacteria
Bea Dorogházi, BSc student, 2013-2015, Development of a next-generation algae-based biohydrogen generation approach
előírt nyelvtudás: angol felvehető hallgatók száma: 1
Jelentkezési határidő: 2015-10-13
2024. IV. 17. ODT ülés Az ODT következő ülésére 2024. június 14-én, pénteken 10.00 órakor kerül sor a Semmelweis Egyetem Szenátusi termében (Bp. Üllői út 26. I. emelet).
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