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Three basic prokaryote shapes: cocci,
spiral and bacilli.
- Cocci are roughly spherical to oval shaped.
- Bacilli are shaped like a prolate ellipsoid, but can appear
filamentous or spindly.
- Spiral shaped prokaryotes.
- There are some variations of these shapes but these are
predominant.
Cell arrangements:
- The final arrangement that the cells take depends on plane
in which the cell divides. In binary fission the planes in which
the cell divide determine arrangement.
- Diplococci are cocci pairs that remain attached create long
chains called streptococci.
- Cocci that divide in two planes and stay attached form
tetrads.
- Division in three planes form cuboidal packets called
sarcinae.
- Clusters of cocci are called staphylococci and they resemble
a bunches of grapes.
- Bacilli have less variability in arrangement because they
divide perpendicular to the long axis.
- The diphtheriae bacteria divide by snapping and they form a
V shape or side by side stacking called palisade.
- In hostile environments some bacteria can form Endospores.
Endospores are not the same as reproductive spores.
Steps of endospore formation:
- DNA is replicated.
- DNA aligns with the long axis of the cell.
- The cytoplasmic membrane invaginates forming the forespore.
- The cell membrane continues to grow and the forespore is
enveloped within a second membrane. The DNA of the vegetative
cell disintegrates.
- A spore coat is formed around the endospore.
- The endospore matures by the completion of the spore coat.
- The endospore is released.
Extremophiles
- Microbes that need extreme conditions of: temperature, pH,
salinity or atmosphere to survive.
DNA Facts
- The DNA of a cell is made up of guanine, cytosine, thymine
and adenine. Guanine pairs with cytosine in DNA. The G+C ratio
refers to the amount, in percent, of guanine and cytosine in a
cells DNA. G+C ratio below 50% are considered log G+C
bacteria. Above 50% G+C ratio is considered high.
Gram-positive bacteria with low G+C ratios have similar 16s rRNA
sequences and those with high G+C have rRNA sequences in common.
- Taxonomists have used the G+C ratio as a criteria for
placing bacteria in phyla.
- Gram positive high G+C bacteria include bacteria that have
rod shaped cells and filamentous bacteria. The latter look like
fungi in how they grow and reproduce and sporulate.
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