Avigad Vonshak

Radically Rethinking Agriculture for the 21st Century

Population growth, arable land and fresh water limits, and climate change have profound implications for the ability of agriculture to meet this century’s demands for food, feed, fiber, and fuel while reducing the environmental impact of their production. Success depends on the acceptance and use of contemporary molecular techniques, as well as the increasing development of farming systems that use saline water and integrate nutrient flows.

EFFECT OF ENVIRONMENTAL CONDITIONS ON FATTY ACID COMPOSITION OF THE RED ALGA PORPHYRIDIUM CRUENTUM: CORRELATION TO GROWTH RATE

The lipid and fatty acid composition of Porphyridium cruentum was determined as a function of light intensity, temperature, pH, and salinity. In cultures cultivated at the optimal temperature under non‐limiting light conditions, eicosapentaenoic acid was the main polyunsaturated fatty acid. When growth rate was reduced by decreased light intensity, increased cell concentration, suboptimal temperature, suboptimal pH, or increased salinity, the content of eicosapentaenoic acid decreased and that of arachidonic acid increased, the latter becoming the major polyunsaturated fatty acid.

Lipid and fatty acid composition of the green oleaginous alga Parietochloris incisa, the richest plant source of arachidonic acid

We have hypothesized that among algae of alpine environment there could be strains particularly rich in long chain polyunsaturated fatty acids (LC-PUFA). Indeed, the chlorophyte (Trebuxiophyceae) Parietochloris incisa isolated from Mt. Tateyama, Japan, was found to be the richest plant source of the pharmaceutically valuable LC-PUFA, arachidonic acid (AA, 20:4omega6). The alga is also extremely rich in triacylglycerols (TAG), which reaches 43% (of total fatty acids) in the logarithmic phase and up to 77% in the stationary phase. In contrast to most algae whose TAG are made of mainly saturated and monounsaturated fatty acids, TAG of P. incisa are the major lipid class where AA is deposited, reaching up to 47% in the stationary phase. Except for the presence of AA, the PUFA composition of the chloroplastic lipids resembled that of green algae, consisting predominantly of C(16) and C(18) PUFAs. The composition of the extrachloroplastic lipids is rare, including phosphatidylcholine (PC), phosphatidylethanolamine (PE) as well as diacylglyceryltrimethylhomoserine (DGTS). PC and PE are particularly rich in AA and are also the major depots of the presumed precursors of AA, l8:3omega6 and 20:3omega6, respectively.

A new tubular reactor for mass production of microalgae outdoors

A novel reactor for outdoor production of microalgae is described. Air-lift is used for circulation of the culture in transparent tubes lying on the ground and interconnected by a manifold. Dissolved O2 is removed through a gas-separator placed 2.0 m above the tubes and water-spray is used for cooling. The manifold permits short-run durations between leaving the gas separator and re-entering it, preventing thereby damaging accumulation of dissolved oxygen. Day temperature control in summer is attained using water-spray. In winter, temperature in the tubes rises rapidly in the morning, as compared to an open raceway even if placed in a greenhouse. The number of hours along which optimal temperature prevails in the culture throughout the year increased significantly. Very high daily productivity computed on a volumetric basis (e.g. 550 mg dry wt l−1 culture) was obtained and preliminary observations indicate that a significantly higher output, e.g. 1500 mg dry wt l−1 d−1 is attainable. Much more research is required to assess the year-round, sustained productivity attainable in this reactor.

Lipid and biomass production by the halotolerant microalga Nannochloropsis salina

The effect of environmental factors on cell-lipid content, on the growth rate and on the overall productivity of Nannochloropsis salina was tested in the laboratory and in outdoor cultures. Under optimum conditions in the laboratory, the maximum growth rate (μmax) was 0·030 h−1, which corresponds to a doubling time of 23 h. Cellular lipid content was affected by the phase of growth and the temperature, but not by nitrogen starvation, pH or the source of sea water. The most important factor affecting the output rate of biomass was the cell concentration. The maximum biomass productivity obtained in outdoor ponds was 24·5 g·m−2·day−1, and the lipid production rate was 4·0 g m−2·day−1.

Mass production of the blue-green alga Spirulina: An overview☆

Progress has been made in the past decade in developing appropriate technology for microalgal mass cultivation. This review details basic requirements required in order to achieve high productivity and low cost of production. There is a need for a wide variety of algal species and strains that will favorably respond to the varying environmental conditions existing outdoors. Another essential requirement is for better bioreactors, either by improving existing open raceway types or developing tubular closed systems. The latter solution seems more promising. These developments must overcome the main limitation confronting the industry today which is the overall low areal yields which fall too short of the theoretical maximum and which are associated with scaling up microalgal culture to commercial size.

Quantitative assessment of the major limitations on productivity ofSpirulina platensis in open raceways

This work represents an attempt to assess the relative contribution of the factors limiting productivity ofSpirulina platensis in open raceways throughout the year. Temperature of the culture during daylight exerted the predominant effect on productivity and elevating the temperature resulted in a significant rise in productivity even in summer. Photoinhibition had a decisive role in summer in determining productivity ofSpirulina in open raceways in that growth almost ceased after mid-day. Contamination by other microorganisms, particularlyS. minor andChlorella sp. was estimated to reduce the net biomass yield by at least 15 to 20%, but measures to curtail the establishment of these species in the raceway have been devised. The effect of harvest time during the day on the yield of dry mass was examined: no conclusion could be drawn except in mid-summer, when evening harvesting resulted in a significant increase in the output rate of dry weight over morning harvesting.It was estimated that in a subtropical climate with little cloudiness, it should be readily possible to obtain an annual output rate of dry mass of ca. 60 to 70 t ha−1. Such output, however, which would reduce very substantially the cost of production to-date, is possible only if the optimal temperature forSpirulina can be maintained throughout daylight, photoinhibition essentially controlled, harvesting in summer performed in the evening, and night-loss of dry mass as well as the extent of contamination by other cyanobacteria or microalgae can be kept low. The pronounced daily fluctuations in the output rate at peak productivity in summer suggest that when environmental limitations of growth are minimal, other limitations become dominant. These should be identified to facilitate an even greater increase in the productivity ofSpirulina in outdoor cultures.

Enhancement and determination of astaxanthin accumulation in green alga Haematococcus pluvialis

Publisher Summary This chapter discusses the enhancement and determination of astaxanthin accumulation in green alga— Haematococcus pluvialis. Astaxanthin is also found in algae, such as Chlamydomonas nivalis and Haematococcus pluvialis, Euglena rubida, and Acetabularia mediterranea. There has been a growing interest in the use of this pigment as a colorant for egg yolk in the poultry industry and in aquaculture, where it is used as a feed supplement in the production of salmon and shrimp. In addition, the carotenoids are lipophilic oxygen quenchers with potential anticancer activities, and it has been shown that this carotenoid possesses a higher antioxidant activity than β -carotene. Research has been done on the conditions favoring accumulation of this ketocarotenoid by the unicellular alga H. pluvialis. It has been suggested that nitrogen deficiency and high light intensity cause massive accumulation of this red pigment in H. pluvialis. Other hypotheses concerning astaxanthin production in H. pluvialis argue either that it is favored by agents that prevent cell division without impairing the ability of the alga to assimilate carbon or the carbon–nitrogen balance in the medium determines the degree of carotene formation. This chapter defines the conditions favoring astaxanthin accumulation in H. pluvialis.

Fatty acid composition of Spirulina strains grown under various environmental conditions

Abstract The fatty acid distribution in 19 strains of Spirulina was studied. All but one contained γ-linolenic acid (GLA). No GLA was found in S. subsalsa, which had a very high content of palmitoleic acid. The fatty acid content of all but one of the tested strains increased with cultivation temperature and the relative amount of polyunsaturated fatty acid decreased. The highest content of GLA was found at 30–35° for most strains. High light intensities at a high temperature (38°), while not affecting the fatty acid composition, had a drastic effect on the fatty acid content, reducing it by as much as 46 %.

MIXOTROPHIC GROWTH MODIFIES THE RESPONSE OF SPIRULINA (ARTHROSPIRA) PLATENSIS (CYANOBACTERIA) CELLS TO LIGHT

Spirulina (Arthrospira) platensis (Nordstedt) Geitler cells grown under mixotrophic conditions exhibit a modified response to light. The maximal photosynthetic rate and the light saturation value of mixotrophic cultures were higher than those of the photoautotrophic cultures. Dark respiration and light compensation point were also significantly higher in the mixotrophically grown cells. As expected, the mixotrophic cultures grew faster and achieved a higher biomass concentration than the photoautotrophic cultures. In contrast, the growth rate of the photoautotrophic cultures was more sensitive to light. The differences between the two cultures were also apparent in their responses to exposure to high photon flux density of 3000 μmol·m−2·s−1. The light‐dependent O2 evolution rate and the maximal efficiency of photosystem II photochemistry declined more rapidly in photoautotrophically grown than in mixotrophically grown cells as a result of exposure to high photon flux density. Although both cultures recovered from the high photon flux density stress, the mixotrophic culture recovered faster and to a higher extent. Based on the above results, growth of S. platensis with a fixed carbon source has a significant effect on photosynthetic activity.