Oedogonium

Oedogonium is a genus of filamentous, free-living green algae, first discovered in the freshwaters of Poland 1860 by W. Hilse and later named by German scientist K.E. Hirn. The morphology of Oedogonium is unique, with an interior and exterior that function very differently from one another and change throughout the life cycle. These protists reside in freshwater systems above and below the equator and are both benthic and planktonic in nature. Forming algal patches on water's surface, they interact closely with a multitude of other algae. These filamentous cell's life cycles include both sexual and asexual reproduction depending on life cycle stage. Although quite common, Oedogonium is difficult to identify since key I.D. factors are only present during reproduction; an uncommon life stage among this genus. Oedogonium has been found to be important in the fixation of heavy metals in fresh water ecosystems. Although K.E. Hirn was the first to publish concerning Odeogoniales, it is not clear as to whether he was the first to discover this new genus. First named Oedogoniaceen (German), Hirn used his knowledge of the Latin language to describe and name the green algal genus; oedos meaning swelling/tumor, and gonos meaning offspring/seed. This name was meant to describe the morphology during sexual and asexual reproduction which he saw and described within his publication, “Monographie und iconographie der Oedogoniaceen”. Oedogonium species were first reported in the late 19th century by Hilse (1860), Gołowin (1964), Kirchner (1878), Kozłowski (1895) and Gutwiński (1897). Hilse was a Polish phycologist who studied freshwater systems in hopes of learning more about microorganisms and how they interacted with their environment. Along with Oedogonium, Hilse is also credited with the discovery and classification of many diatoms. Mrozińska was the first to exam this group in terms of morphology, ecology and distribution and in his time described more than 400 species – mainly from southern Poland. In 1900, German scientist K.E. Hirn wrote a monograph concerning his finding of a new taxon, to which he promptly gave the name Oedogoniaceen – now Oedogonium. This paper was published and translated 60 years later. Hirn discovered Oedogonium in a ditch, appearing from June – October, but not much else is known as this was his only published contribution and he died in 1907 (7 years following his discovery). Since this 1900 monograph, this taxon has been vital in ongoing studies regarding biosorption of heavy metals – particularly lead – from fresh water ecosystems. Identification of species within Oedogonium is extremely difficult since I.D. factors are mainly based on reproductive characters, and very rarely are species in this genus discovered in their reproductive state. For the most part they exist in a filamentous form. In 1991 a paper by Mrozińska presented a new taxonomic classification of the genus Oedogonium and a proposed division into two sections: I. Monospermatozoideae and II. Dispermatozoideae. These sections were based on the different number of spermatozoids the antheridial (male sex organ containing) cell expresses. This classification is not widely accepted, as it still requires support through further studies. Cells of the genus Oedogonium are narrow and cylindrical in shape. The algal body consists of green, un-branched, and multi-cellular filaments, arranged end to end. Every cell of the filamentous algal body (called the thallus) is similar in shape apart from the apical cell (the uppermost) and the holdfast cell (the lowermost). The apical cell is wider and always rounded at its tip (having a cap) relative to the other cells of the thallus. The holdfast cell, however, produces elongated growths from both unattached sides which aid in firmly attaching the filament to substrate. The holdfast is also the only colourless cell of the filament. All other cells in the filament exist as green structures very similar in nature, with only some cells having caps. The number of caps per cell illustrates the number of times that cell has divided. Every cell of the filament has a cell wall consisting of three layers – the innermost is made of cellulose, the middle of pectose, and the outermost is made of chitin. These three layers provide rigidity and protection for these benthic species. Most cells are attached to the substrate by the holdfast and are vegetative cells, although some are free-floating.Species of Oedogonium are divided into two major groups based on distribution of the sex organs: macrandous and nannandrous species. Macrandous species have a male sex organ (the antheridia) and female sex organ (the oogonia) produced on filaments of normal size. This group is further subdivided into macrandous monoecious and macrandous dioecious. In macrandous monoecious species, the antheridia and oogonia are always found on the same filament. In contrary, in macrandous dioecious species, the antheridia and oogonia are produced on different filaments. Although filaments bearing antheridia and oogonia are morphologically similar, they differ physiologically. In nannandrous species, filaments producing antheridia and oogonia show morphological distinction. The antheridia, which are much smaller than the oogonia, are called dwarf male. Nannandrous species are always dioecious; i.e. antheridia and oogonia are always produced on different filaments. Small male filaments are likely to be attached to a female filament, near an oogonium. The protoplasm of Oedogonium is contained by a plasma membrane, and consists of a single nucleus, reticulate chloroplasts, cytoplasm and a central vacuole. Cell sap (contained by the central vacuole) is made up of inorganic compounds, excretions and secretions. Between the innermost cell wall and the central vacuole is a thin layer known as the protoplast. The single nucleus is large and oval shaped and sits in the centre of the cell – usually along the membrane and internal to the chloroplast. This large nucleus contains 1-2 nucleoli and elongated chromosomes. The reticulate, parietal chloroplast extends over the whole interior of the cell, enveloping the protoplast. Whether these networked strands are narrow or broad varies between species, but with most species these reticula are parallel to the long axis of the cell. At the strand junctions are pyrenoids, covered in starch plates. Cells of Oedogonium also contain very typical Golgi bodies, mitochondria, and endoplasmic reticulum.