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Hallo Oilgae friends,

just in another group "Algae to Growdiesel" the following question popped up:
How many photons does it take to make one gram of Nannochloropsis Oculata in an optimal concentration PBR setting?

A tricky question!? Yes indeed, and after the experience we made can this only be soled with practical experience.

 

The light used for the cultivation of phototrophic micro-organisms has to be in the spectral range of ~, 400 to 700 nm to activate the photosynthesis pigments [Heath, in 1972; Lawlor, in 1992]. An optimum irradiation strength (number of photons per surface needed and time [μE m-2 s-1], the photo synthetic photon flux density (PPFD) is different from specie to specie and can be derived from the light saturation curve.

Below minimum irradiation strength a photosynthetic driven micro-organism will use more energy for his (preservation) metabolism than it could get from the irradiated light (measurable photosynthesis rate and total oxygen balance negative).

The minimum necessary irradiation strength for a measurable positive photosynthesis rate will show in the light saturation curve and be market as light compensation point [Goldmann, in 1979; Kohl and Nicklisch, in 1988]. A growing PPFD rate will result in the production of oxygen until it reaches a constant maximum level of oxygen saturation. In the linear area of the light saturation curve every photon will be photo-chemical absorbed by photosynthesis pigments thus enabling the photosynthesis process. The photon exploitation at this level is at its maximum (maximum quantum yield); however, the growth rate of photosynthesis-active organisms is limited due to low a light intensity. We are now in the transition area of the light saturation curve when the photosynthesis rate is at its highest level but the amount of photons used for the photosynthesis are at a minimum. The light saturation is based on the limited reaction rate of plastoquinone or the oxidation of NADPH (Nicotinamide adenine dinucleotide phosphate) molecules in the Calvin cycle [Matthijs et al., 1996]. A part of the electrons animated in the PS II (photo synthesis system II/Calvin curve) can not be used, but this energy is being converted into warmth and fluorescence. Raising the light intensity may now result in a photo inhibition (reducing the photosynthesis rate) and may destroy photosynthesis receptors, light-absorbent pigments and the thylakoid membran [Hopkin

and H?ner, in 2004].

The density of cells during cultivation will lead to an increasing shading effect which will have to be compensated by an adjustment of light entry. As a result this limitation of light during the growths will not leave enough protons available for an optimal supply. Contradictory too much light entry in the beginning of cell cultivation would cause cell damage (photo inhibition). Another parameter which influences the light entry is the upper surfaces /

Volume (A/V) - relation of the photo bioreactor.

A homogeneous irradiation of all cells combined with an ideal A/V-relation, this in connection with a sufficient mixing would prevent a continuous change of light conditions from the unlit centre of the reactor to the illuminated surface.

 

If light is so vitally important for algae, - as much as too much light is damaging, - just how much light do we need for algae breeding in a PBR system?

And what can we learn from all this?
They need light, off course, but are shy of direct solar radiation. How can we measure how much light? We use a patented Model-Reactor (Pat.Nr. 202007013 401.1) with an LED light source to find out the optimum growth level of algae species. Here we can simulate the light conditions of
Germany, Spain, Australia or even India. Also different nutrition requirements can be tested. It has shown for us that here in Central Europe only 10% of solar radiation is necessary to achieve an optimum growth rate. Thus algae cells are converting 5% of the given light into bio energy (something that i.e. the sugar cane can only do with 1% effectiveness). We are able to boost the productivity of algae up to 100 gram per m? per day with this method of finding the right specie. But we even learned more. In a compact algae culture which is mixed up by streaming water, some algae will come into the (light) surface, some will return into the dark. From the view of an algae cell it might appear as if the light is flickering. This Disco-light effect was researched as well. Surprisingly the algae liked it very much! They are able to store the captured light and will use it later, in the dark, for their growth.

 

So how could you measure your light intensity compared to what you have as equipment (type of reactor), and to find out with the help of a light saturation curve just how much light you may need (that you will be able to find out just how much photons you may need per cell I may have the freedom not to believe?.. this was a joke, wasn?t it?) for optimum growth.

You would need a good photo meter (Quantum Sensor to measure photo synthetically active radiation (PAR ? LI-COR Biosiences) and at least 6 til 12 month time to go through all possible light conditions with your PBR. Good Luck!

You may see the ?Specification ?bio reactor? which you will find on my profile. You may notice that we are working with a continuous harvesting system that gives an excellent control over the cell density in our reactor model. Thus we can keep productivity high do not have to stress with light limitation factors through shading. And we work with greenhouses, - not only because of  our northern Europe climate! ? no, we even shade our cultures up here in the north.. Andreas-Algae Nova

NB. Just one little question I have, - if you have an optimal PBR setting, why do you want to count photons?
It`s a waste of time than.......
Fri October 08 2010 02:59:29 PM by AlgaeNova photons  |  light  |  cell cultures  |  PBR  |  photosynthesis 1913 views

Comments - 4

  • Fri October 08 2010 06:34:28 PM

    Andreas, this is an excellant post!!!

    Alan Schaefer

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  • Fri October 08 2010 11:15:36 PM

    " They are able to store the captured
    light and will use it later, in the dark, for their growth."

    Do they absorb CO2 in the nights with the stored light ?

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  • Emily wrote:
    Sat October 09 2010 03:11:08 AM

    Not long ago Andreas Abhram posted this in a blog.

    "
    As long as you are not in arctic regions, where there is no light at all during winter month, - don`t bother about additional light for algae growing.

    All you achieve with artificial light sources in or around tanks is, that the algae tries to orientate itself towards the light.

    As it is in nature the stronger will get all the light and than it is just like in the good old song about Mac the Knive:

    "And some are in the darkness
    And the others in the light
    But you only see those in the light
    Those in the darkness you don't see"

    - and they won`t grow that much either.
    Believe me, - we have tried it.........
    (see the articel about light management).

    Good mixing and possibly constant, warm temperatures and adequate nutrition are much more importand than exagerated light shows.

    "

    No comments from me.

    Awaiting comments from AA and others:-)

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  • AlgaeNova wrote:
    Wed October 13 2010 07:19:51 AM

    In case something should not be clear by now, please read this articel:

    Researchers show how algae make surplus light energy harmless

    Light is of vital importance. However, excessive sunbathing causes sunburn - and not only in people and animals. Intensive exposure to sunlight can be harmful for plants, too. A team of scientists from M?nster and the USA have now been able to show for the first time how green algae protect themselves against such damage. The journal "Nature" carries a report on this in the issue published on 26 November 2009.
    Plants are dependent on sunlight for growth. With the aid of light energy they produce sugar molecules which are converted into components of their cells and act as suppliers of energy. In this process plants extract carbon dioxide from the atmosphere and release oxygen. This process - called photosynthesis - is the basis of all life on earth. "Photosynthesis provides the vegetable biomass - and thus the basis of food supply - for people and animals," says Prof. Michael Hippler from the Institute of Biochemistry and Plant Biotechnology at M?nster University.

    However, using light energy to produce biomass is a tricky business for plants. The absorption of light through cellular pigment molecules, e.g. through chlorophyll, can lead to the production of oxygen radicals in plants and thus damage them. "In order to protect themselves from such oxidative destruction - 'sunburn', so to speak," says Prof. Hippler, "plants have developed mechanisms for converting the surplus light energy into heat energy. Although algae produce a large share of the biomass generated worldwide, very little was known up to now about this protective mechanism in algae - in contrast to flowering plants." An international team of scientists led by Prof. Hippler and Prof. Kris Niyogi from the University of California in Berkeley, USA, have now thrown light on this sun protection mechanism in the unicellular green alga Chlamydomonas reinhardtii.

    The sun protection factor is a certain light-harvesting protein (LHCSR3). "In general," explains Prof. Hippler, "such proteins harvest light - as their name suggests - and they make it available for photosynthesis. In this particular case, however, the protein permits the conversion of light energy to heat energy and in the process it renders the surplus light energy harmless." In comparison to traditional light-harvesting proteins, LHCSR3 has very old origins, probably stemming directly from the 'forebear' of all light-harvesting proteins. If there is any obstacle to the production of this protein, the algae are no longer able to dissipate harmful excess energy. They then get 'sunburn', which can in fact result in the alga cells dying.

    "Interestingly, flowering plants have lost these protein molecules during their evolution and have developed another sun protection mechanism in which light is also converted into heat energy," says Prof. Hippler. "The discovery of the 'sun protection factor' in algae makes it possible for us to have deep insights into the regulation of aquatic photosynthesis, which is responsible for 50 percent of the primary production of biomass worldwide." Moreover, he says, the insights could be used to optimize the culture of micro-algae in bio-reactors. In this way the biotechnological production of biomass from algae could be improved, e.g. for the production of bio-fuels.

    Reference:
    Peers G. et al. (2009): An ancient light-harvesting protein is critical for the regulation of algal photosynthesis. Nature 462, 518-521; doi: 10.1038/nature08587
    Weitere Informationen:
    http://www.nature.com/nature/journal/v462/n7272/full/nature08587.html literature
    http://www.uni-muenster.de/hippler/ AG Hippler
    URL dieser Pressemitteilung: http://idw-online.de/pages/de/news346073
    Merkmale dieser Pressemitteilung:
    Biologie
    ?berregional
    Forschungsergebnisse, Wissenschaftliche Publikationen

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