Explore the fundamental features that distinguish Gram-positive bacteria from Gram-negative bacteria, including cell wall structure, staining properties, and biochemical characteristics.
Gain insights into the major genera of Gram-positive bacteria, including Staphylococcus, Streptococcus, Bacil...
Actinobacteria- High GC gram-positive bacteria - over 50%
- Streptomyces
- Corynebacteria
- Mycobacteria
Mycoplasmas - The Mollicutes ('soft skin bacteria')
These bacteria completely lack cell wall and have only plasma membrane.
Therefore they stain gram negative but sequencing of their genes reveal that they are
clearly phylogenetically related to the low GC gram positives (Lactobacillus -
Clostridium branch).
Sensitive to osmotic lysis, plasma membrane is strengthened by inclusion of sterols.
Plasma membrane may also include lipoglycans (heteropolysaccharide linked to the
membrane lipids) and lipoprotein - involved in avoiding the immune response.
Pleomorphic: big, small, long, branched
The coccoid cells 0.12 micrometre - 0.25 micrometre in diameter are probably the
smallest living cells.
Easily deformable cells that can squeeze into different shapes.
Growth of Mycoplasmas
All are parasite of eukaryotes.
Many can be grown outside of cells in lab media.
Mycoplasma can have complex growth factor requirements due to their Limited
biosynthetic capabilities
All require sterols except Archoleplasma, Asteroleplasma and Mesoplasma
Many require a variety of vitamins, fatty acids, amino acids, purines and pyrimidines.
On solid agar they form a fried egg shaped colony and embed into the media.
Mycoplasma Genomics
GC content approx. 25-35% depending on the species.
Mycoplasma genitalium has the smallest known genome of any self-replicating
organism measuring only 580 kbp and encoding 472 genes.
Close to the smallest amount of DNA capable of encoding a living cell.
Because they have evolved to live in such close parasitic association with eukaryotic
hosts and managed to get rid of the genes they don't need over the evolution as they
can gain the nutrients from the host they've invaded, which eventually reduced their
genome size.
Gram Positive Bacteria Page 1
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