Planctomycetes

Planctomycetes are an orderof obligately aerobic[requires atmospheric oxygen for growth] aquatic bacteria and are found in field samples of brackish and marine as well as freshwater samples. They reproduce by budding. In structure, the organisms of this group are ovoid and have a holdfast at the nonreproductive end that helps them to attach to each other during budding, called the stalk.

Structure

The organisms belonging to this group lack mureinin their cell wallMurein is an important heteropolymer present in most bacterial cell walls that serves as a protective component in the cell wall skeleton. Instead their walls are made up of glycoproteinrich in glutamate. Planctomycetes have internal structures that are more complex than would be typically expected in prokaryotes. While they don't have a nucleusin the eukaryoticsense, the nuclear material can sometimes be enclosed in a double membrane. In addition to this nucleoid, there are two other membrane-separated compartments; the pirrellulosome or riboplasm, which contains the ribosomeand related proteins, and the ribosome-free paryphoplasm (Glockner, 2003).

Genome

RNA sequencing shows that the planctomycetes are distantly related to the eubacteria. A number of essential pathways are not organised as operons, which is unusual for bacteria (Glockner, 2003). A number of genes have been found (through sequence comparisons) that are similar to genes found in eukaryotes. One such example is a gene sequence (in Gemmata obscurioglobis) that was found to have significant homology to the integrinalpha-V, a protein that is important in transmembrane signal transduction in eukaryotes (Jenkins et al., 2002).

Life cycle

The life cycle involves alternation between sessile cells and flagellatedswarmer cells. The sessile cells bud to form the flagellated swarmer cells which swim for a while before settling down to attach and begin reproduction.

References

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This article is licensed under the GNU Free Documentation License.
It uses material from the http://en.wikipedia.org/wiki/Planctomycetes Wikipedia article Planctomycetes.