Earlier this spring I collected some samples of algae for my botany class to observe and managed a small sample of Chara, also known as muskgrass, to put in the lab. It has been growing well with frequent water changes and has developed lots of the reproductive structures called gametangia (structures that produce gametes, or sperm and eggs). The type of gametangia that produce sperm are called antheridia and are seen as the bright orange structures in image below.
And here is a closeup of an antheridium
Somewhat less abundant are the oogonia, where eggs are produced and where fertilization takes place. The oogonia on this particular specimen have an interesting twist to them, although I do not know if this is typical of all Chara spp. or just this one.
I’ve been watching March Madness on demand (ncaa basketball) and just about every other commercial has been for ExxonMobil’s foray into algal oil research. Having studied algae a bit this subject has peeked my interest. Exxon has partnered with Synthetic Genomics, Inc to study the potential of algae as a source of bio-fuels and is expected to devote in excess of $600 million to this research.
This is not an entirely new concept but it appears to be one of the largest investments in algal oil research to date. A great deal is known about culturing algae for other uses. Algal cultures are used extensively in aquaculture of clams and oysters. About 40% of the costs of producing juvenile bivalve seed in a hatchery is from the production of algae cultures.
Many algae reproduce rapidly when sufficient light, CO2, and nutrients are supplied. Anyone who has kept an aquarium or pond is probably familiar with algae blooms. Commercial ventures must maintain pure stock cultures since eventual contamination with other organisms eventually causes algal populations to crash, and this adds to the cost of culturing algae on a large scale.
It happens that many of the species that my students examine in the classroom have been investigated as possible algal oil sources. These include the filamentous green algae Oedogonium and Spirogyra. These are probably more familiar to people as components of “pond scum”, which makes the potential use of these organisms for bio-fuels all the more interesting.
Algae in the genus Spirogyra are known for their unbranched, filamentous thalli containing long, spirally arranged chloroplasts within each cell.
Sexual reproduction in Spirogyra occurs via conjugation, where two adjacent filaments form connections (conjugation tubes). The contents of the joined cells serve as isogametes (Raven et al., 2007). In the images below the isogametes from one filament can be seen moving into the cells of another filament. Where they meet they form a zygote.
Raven, P.H., Evert, R.F., and S.E. Eichhorn. 2007. Biology of Plants, 7th ed. Worth Publishers, Inc., NY.
It would seem that the subject of my posts keep getting smaller and smaller. These images are of a common green algae (phylum Chlorophyta) commonly known as Water Net. It gets its name from the pentagonal or hexagonal branching pattern of the filaments making up the body (thallus) of the algae. These specimens came in on a sample of Chara, another green algae that is considered to be the closest living relative to plants. I took a sample of the Chara out the other day to photograph and left the sample in a dish of water under some lights. After about a week these little green ‘bubbles’ started appearing and have continued to get progressively larger.
I was really curious what this stuff was but couldn’t really find anything that fit the description. I was already aware that water net was growing in the tank where I am keeping the Chara, but the filaments on these were not visible to the naked eye. It wasn’t until I got out a hand lens that they became apparent.
Apparently they can form these somewhat spherical colonies that just keep expanding as the thallus divides. I got one good closeup showing how each filament is connected to two other filaments, which creates the unique branching pattern and allows the colony to take on a 3-dimensional form.
Algae in the genus Hydrodictyon are isogamous (gametes all alike) and the cells are coenocytic (multinucleate). Dictyo is Greek for net-like, so the genus means the same as the common name.