Photofermentation

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Photofermentation is the fermentative conversion of organic substrate to biohydrogen manifested by a diverse group of photosynthetic bacteria by a series of biochemical reactions involving three steps similar to anaerobic conversion. Photofermentation differs from dark fermentation because it only proceeds in the presence of light.

Contents

For example, photo-fermentation with Rhodobacter sphaeroides SH2C (or many other purple non-sulfur bacteria [1] ) can be employed to convert small molecular fatty acids into hydrogen [2] and other products.

Depicts general process of photofermentation. General process of photofermentation - 12934 2015 324 Fig1.gif
Depicts general process of photofermentation.

Light-dependent pathways

Phototropic bacteria

Phototropic bacteria produce hydrogen gas via photofermentation, where the hydrogen is sourced from organic compounds. [4]

[4]

Photolytic producers

Photolytic producers are similar to phototrophs, but source hydrogen from water molecules that are broken down as the organism interacts with light. [4] Photolytic producers consist of algae and certain photosynthetic bacteria. [4]

(algae) [4]

(photolytic bacteria) [4]

Sustainable energy production

Photofermentation via purple nonsulfur producing bacteria has been explored as a method for the production of biofuel. [5] The natural fermentation product of these bacteria, hydrogen gas, can be harnessed as a natural gas energy source. [6] [7] Photofermentation via algae instead of bacteria is used for bioethanol production, among other liquid fuel alternatives. [8]

Basic principles of a bioreactor. The photofermentation bioreactor would not include an air pathway. Bioreactor principle.svg
Basic principles of a bioreactor. The photofermentation bioreactor would not include an air pathway.

Mechanism

The bacteria and their energy source are held in a bioreactor chamber that is impermeable to air and oxygen free. [7] The proper temperature for the bacterial species is maintained in the bioreactor. [7] The bacteria are sustained with a carbohydrate diet consisting of simple saccharide molecules. [9] The carbohydrates are typically sourced from agricultural or forestry waste. [9]

Variations

Depiction of algae (species not specified) in a bioreactor suitable for bioethanol production. Green algae in a bioreactor.jpg
Depiction of algae (species not specified) in a bioreactor suitable for bioethanol production.

In addition to wild type forms of Rhodopseudomonas palustris, scientists have used genetically modified forms to produce hydrogen as well. [5] Other explorations include expanding the bioreactor system to hold a combination of bacteria, algae or cyanobacteria. [7] [9] Ethanol production is performed by the algae Chlamydomonas reinhardtii , among other species, in cycling light and dark environments. [8] The cycling of light and dark environments has also been explored with bacteria for hydrogen production, increasing hydrogen yield. [10]

Advantages

The bacteria are typically fed with broken down agricultural waste or undesired crops, such as water lettuce or sugar beet molasses. [11] [5] The high abundance of such waste ensures the stable food source for the bacteria and productively uses human-produced waste. [5] In comparison with dark fermentation, photofermentation produces more hydrogen per reaction and avoids the acidic end products of dark fermentation. [12]

Limitations

The primary limitations of photofermentation as a sustainable energy source stem from the precise requirements of maintaining the bacteria in the bioreactor. [7] Researchers have found it difficult to maintain a constant temperature for the bacteria within the bioreactor. [7] Furthermore, the growth media for the bacteria must be rotated and refreshed without introducing air to the bioreactor system, complicating the already expensive bioreactor set up. [7] [9]

See also

Related Research Articles

<span class="mw-page-title-main">Bioreactor</span> System that supports a biologically active environment

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<span class="mw-page-title-main">Hydrogen cycle</span> Hydrogen exchange between the living and non-living world

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<span class="mw-page-title-main">Biohydrogen</span> Hydrogen that is produced biologically

Biohydrogen is H2 that is produced biologically. Interest is high in this technology because H2 is a clean fuel and can be readily produced from certain kinds of biomass, including biological waste. Furthermore some photosynthetic microorganisms are capable to produce H2 directly from water splitting using light as energy source.

<span class="mw-page-title-main">Fermentation</span> Metabolic redox process producing energy in the absence of oxygen.

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<i>Rhodobacter sphaeroides</i> Species of bacterium

Rhodobacter sphaeroides is a kind of purple bacterium; a group of bacteria that can obtain energy through photosynthesis. Its best growth conditions are anaerobic phototrophy and aerobic chemoheterotrophy in the absence of light. R. sphaeroides is also able to fix nitrogen. It is remarkably metabolically diverse, as it is able to grow heterotrophically via fermentation and aerobic and anaerobic respiration. Such a metabolic versatility has motivated the investigation of R. sphaeroides as a microbial cell factory for biotechnological applications.

Dark fermentation is the fermentative conversion of organic substrate to biohydrogen. It is a complex process manifested by diverse groups of bacteria, involving a series of biochemical reactions using three steps similar to anaerobic conversion. Dark fermentation differs from photofermentation in that it proceeds without the presence of light.

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References

  1. ↑ Redwood MD, Paterson-Beedle M, Macaskie LE (June 2009). "Integrating dark and light bio-hydrogen production strategies: towards the hydrogen economy" (PDF). Reviews in Environmental Science and Bio/Technology. 8 (2): 149–185. doi:10.1007/s11157-008-9144-9. S2CID   83562378.
  2. ↑ Tao Y, Chen Y, Wu Y, He Y, Zhou Z (February 2007). "High hydrogen yield from a two-step process of dark-and photo-fermentation of sucrose". International Journal of Hydrogen Energy. 32 (2): 200–6. doi:10.1016/j.ijhydene.2006.06.034.
  3. ↑ Gabrielyan, Lilit; Sargsyan, Harutyun; Trchounian, Armen (2015-09-04). "Novel properties of photofermentative biohydrogen production by purple bacteria Rhodobacter sphaeroides: effects of protonophores and inhibitors of responsible enzymes". Microbial Cell Factories. 14 (1): 131. doi: 10.1186/s12934-015-0324-3 . ISSN   1475-2859. PMC   4558839 . PMID   26337489.
  4. 1 2 3 4 5 6 Ghimire A, Frunzo L, Pirozzi F, Trably E, Escudie R, Lens PN, Esposito G (April 2015). "A review on dark fermentative biohydrogen production from organic biomass: Process parameters and use of by-products" (PDF). Applied Energy. 144: 73–95. doi:10.1016/j.apenergy.2015.01.045.
  5. 1 2 3 4 Corneli E, Adessi A, Olguín EJ, Ragaglini G, García-López DA, De Philippis R (December 2017). "Biotransformation of water lettuce (Pistia stratiotes) to biohydrogen by Rhodopseudomonas palustris". Journal of Applied Microbiology. 123 (6): 1438–1446. doi:10.1111/jam.13599. hdl: 2434/837874 . PMID   28972701. S2CID   4312887.
  6. ↑ Laurinavichene T, Tekucheva D, Laurinavichius K, Tsygankov A (March 2018). "Utilization of distillery wastewater for hydrogen production in one-stage and two-stage processes involving photofermentation". Enzyme and Microbial Technology. 110: 1–7. doi:10.1016/j.enzmictec.2017.11.009. PMID   29310850.
  7. 1 2 3 4 5 6 7 Uyar B (September 2016). "Bioreactor design for photofermentative hydrogen production". Bioprocess and Biosystems Engineering. 39 (9): 1331–40. doi:10.1007/s00449-016-1614-9. PMID   27142376. S2CID   31956368.
  8. 1 2 Costa RL, Oliveira TV, Ferreira J, Cardoso VL, Batista FR (April 2015). "Prospective technology on bioethanol production from photofermentation". Bioresource Technology. 181: 330–7. doi:10.1016/j.biortech.2015.01.090. PMID   25678298.
  9. 1 2 3 4 Zhang Q, Wang Y, Zhang Z, Lee DJ, Zhou X, Jing Y, Ge X, Jiang D, Hu J, He C (April 2017). "Photo-fermentative hydrogen production from crop residue: A mini review". Bioresource Technology. 229: 222–230. doi:10.1016/j.biortech.2017.01.008. PMID   28108074.
  10. ↑ Chen CY, Yang MH, Yeh KL, Liu CH, Chang JS (September 2008). "Biohydrogen production using sequential two-stage dark and photo fermentation processes". International Journal of Hydrogen Energy. 33 (18): 4755–4762. doi:10.1016/j.ijhydene.2008.06.055.
  11. ↑ Keskin T, Hallenbeck PC (May 2012). "Hydrogen production from sugar industry wastes using single-stage photofermentation". Bioresource Technology. 112: 131–6. doi:10.1016/j.biortech.2012.02.077. PMID   22420990.
  12. ↑ Chandrasekhar K, Lee YJ, Lee DW (April 2015). "Biohydrogen production: strategies to improve process efficiency through microbial routes". International Journal of Molecular Sciences. 16 (4): 8266–93. doi: 10.3390/ijms16048266 . PMC   4425080 . PMID   25874756.
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