Molecular Inquires and Research


rRNA sequencing

With regards to distinguishing certain organisms to taxonomic sections, molecular investigations have been done for an evaluation of the Order Gigartinales. Under current classifications, Plocamium cartilagineum has been placed under the Order Gigartinales (Sze 1998).

According to Saunders and Kraft, there is evidence that the Family Plocamiaceae could be more specifically placed under their proposed Order Plocamiales (1994). This is a new Order, and evidence for the proposed Order is based on the rRNA sequencing of the genera Plocamium and Plocamiocolax, which are both under the family Plocamiaceae. These experiments were carried out molecularly, using the small-subunit rRNA gene (SSU). Saunders and Kraft conclude that under SSU sequencing the two genera differ greatly in nucleotide sequence from the Gigartinales genera Sphaerococceae, Phacelocarpaceae, and Nizymeniaceae. Therefore, Saunders and Kraft conclude that Plocamiocolax shares a "sister" relationship with Gigartinales rather than being a member of that order.

The SSU sequencing has been used widely for the grouping of organisms to families and genera, or for the construction of taxonomic trees. The SSU sequencing is a powerful tool for molecular systematics as it adds further analysis in the sequencing classification, which is lead by DNA sequencing. Most of these sequences are available on the World Wide Web.

Natural products of Plocamium cartilagineum

Plocamium cartilagineum is under much research currently because it naturally produces halogenated monoterpenes which can be isolated. Monoterpenes are hydrocarbons and "to be halogenated" means to have a halogen element from the V11 column (Cl, Br, I, etc.) of the periodic table. The biological role of the halogenated monoterpenes is one of cytotoxicity, which means "toxic to cells". According to a study from Chile, the halogenated monoterpenes of seaweed from the family Plocamiaceae produce molecules that are antimicrobial, antifeedant, and antifungal. (Konig, Wright and De Nys 1999).

Bacterial symbiont relationship

Plocamium cartilagineum also produces a biopolymer that is believed to be of bacterial origin. This biopolymer is coded for by a bacterium, which indicates that Plocamium formed a symbiotic associated with a bacterium somewhere in its history. (Abreu, Galindro, Relva, and Ramos 1997)

Antarctic Plocamium cartilagineum

Plocamium cartilagineum can exist and thrive in Antarctic conditions. It is able to adapt to the extreme cold and carry on normal molecular mechanisms. When P. cartilagineum is heat shocked at 5 ºC it displays induction of mRNAs that encode for the heat shock protein, HSP 70, and ubiquitin polyprotein, UBI (Vayda and Yuan 1994). The maximum induction is at 10 ºC, however, at 20 ºC cell death occurs. What is unusual is that even though Antarctic P. cartilagineum never experiences such extremes, it is capable of responding to severe heat shock.


Genetic sequences for the Plocamiales can be found at the Taxonomy Browser.

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© 1999 Nilauro Markus, Marla Ranelletti, Christopher Loo