Physiology and Cultivation of
Algae and Cyanobacteria
6.
Culture methods
• Batch cultures
– common, simple, low cost, closed system, volume-limited
– any flow of nutritions & products
– Erlenmeyer flasks, tubes, Petri dishes
– growth curve phases – lag, acceleration, exponential, retardation,
stationary, decline
Culture methods
• Continuous cultures
– resources are potentially infinite
– cultures are maintained at chosen point on the growth
curve by regulated addition of fresh medium
– air pump – CO2 source, mixing
– categories of contin. cult.:
• turbidostat cultures
• chemostat cultures
• Semi-continuous cultures
– periodic fresh medium addition & harvesting
Culture methods
• Commercial-scale cultures
– volume of cca. 102 – 109 l
– large open ponds, circular ponds with rotating arm, raceway
ponds, large bags, tube system
– factors to be considered:
• biology of alga; the cost of land; labor; energy; water; nutrients; climate (if outdoors);
type of product
• light utilization efficiency (PBR & open ponds, surface-to-volume ratio 20-200 vs 5-10m-
1, orientation, inclination); ability to control temp.; hydrodynamic stress (mixing); oxygen
accumulation; ability to maintain culture unialgal or axenic (photobioreactors vs. open
ponds)
-scale up ability
• Harvesting (20-30%cost) – species specific
– Flocculation -↑pH, cationic polymers (Chitosan, Zetag)
– Centrifugation & filtration
• Dehydrating – sun-drying, spray-drying, drum-drying, freeze-drying
• Cell disruption – mechanical (homogenizers, bead mills, ultrasound), chemical
• Product isolation and purification
– Chlorella, Spirulina, Dunaliella, Nannochloropsis
Methods used for
algal culture growth evaluation
• direct
– fresh/dry mass determination
– counting – number of cells (colonies)
– cell volume, PCV
– protein content
– calorific value
– flow-cytometry & epifluorescence microscopy
• indirect
– turbidity; optical density
– chlorophyll content
Algae & Men
• macroalgae (commerce - 42 countries)
• food
– Laminaria (China, N.,S.Korea, Japan, Philipines, Chile, Norway,
Indonesia, U.S., India)
– Porphyra, Kappaphycus, Undaria (Wakame), Euchema, Gracilaria,
Caulerpa lentillifera (green caviar)
– Nori (Porphyra yezzoensis) – 13mil. t/y
• microalgae
• carotenoids, pigmenst, proteins, vitamins, …
– Dunaliella, Haematococcus, Arthrospira, Chlorella
– nutraceuticals, pharmaceuticals, animal feed additives, cosmetics, fertilizers
– N2-fixing cyano.-biofertilizers in rice fields
– Wastewater oxidation, bioremediation
• Microalgae – platform for recombinant proteins (e.g. hGH in Chlorela)
Algae & energy
• Biodiesel
– Algal fatty esters or vegetable oils or animal fats
– "B" factor (biodiesel in fuel)
• Oil Extraction
– 1. Expeller/Press; 2. Hexane solvent oil extraction; 3. Supercritical
Fluid extraction; Enzymatic extraction; Osmotic shock; Ultrasonicassisted
Extraction
• Ethanol from algae
– high carbohydrate content (Sargassum, Glacilaria, Prymnesium
parvum, Euglena gracilis)
• Cultivation of algae for CO2 capture
– can absorb over 2 million tons of Co2 a year per acre
Endogenous rhythms
• Chronobiology
– free-running vs. entrained (synchronized)
• circadian rhythms
• molecular feedback loop ~ 24h~ environmental light-dark
cycles ~ positive/negative phase shifts according to phaseresponse
curve of particular response
• necessity to transfer sunlight-sensitive processes into the night
(cell division in night)
• lost under certain conditions (e.g. constatnt light, bright light,
growth of Euglena on organic medium)
– phototaxis
– timing of cell division
– photosynthetic capacity
– bioluminiscence
– gene expression
– sensitivity to UV
Endogenous rhythms
• biweekly (circa-semilunar) rhythms
• wave action (sea may reduce gamete concentration of marine org.
with external fertilization)
• e.g.:brown alga Dictyota dichotoma releases eggs twice a month in
the field; synchronization signal every second full-moon light
• day-length effect (photoperiodism)
• circadian timer measures length of night and triggers photoperiodic
response
• LD (12:12~light:dark) – induce upright thali formation
• SD (8:16)– induce reproductive organs formation
• circannual rhythmicity
• sequence of short and long days over the years results cyclic
reproductive stages formation (e.g. Ascophyllum, Laminaria)
• signal probably temporal sequence of different physiological stages
Documetation
• Microscopy (light & fluorescence)
– drawings
– photography – classic & digital
• algal culture collections
• Web pages of culture collections in the world:
https://www.eccosite.org/
• macroalgae ~ herbarium