Question

1) Describe the types of bacterial cell arrangements and how the different planes of cell division determine their arrangements. Why Bacilli are less varied in arrangement than cocci? 2) Mycoplasmas are classified as Low G + C Gram-Positive Bacteria in the textbook. However their staining phenotype indicates they are gram negative. What is the basis for classification as gram positive bacteria? 3) Make a dichotomous key to distinguish among the orders of Gammaproteobacteria

Answer 1

Answer:-

1. There are various kind of shapes are found in bacterial cell such as cocci, bacilli, spiral. It's the cell division which determine the arrangement of cells in bacteria at different plane of axis. In case of cocci ( spherical in shape), different arrangement of cells have been identified which include Diplococcus(occur in the form of pair like 2,4 due to single plane of division),Streptococcus( occur due division in single plane just like diplococcus and results in chain like arrangement), Tetrad(means four cocci are arranged due to the division in two planes), Staphylococcus( division at random planes results in cluster of grapes like arrangement). In case of bacilli ( rod in shape), different arrangement takes place through single plane cell division which results in Bacillus, Streptobacilli( bacilli are arranged in chains),coccobacilli(similar to coccus). In case of spiral, there are three different forms include in it such as vibrio( comma shaped rod ), spirillum (thick and rigid), spirochete ( thin and flexible and having helically coiled cells). Bacillus are less varied in arrangement than cocci because Bacillus can only divide end to end in single plane of division and lead to the formation of chain like arrangements whereas, cocci can form different type of arrangement of cells as they can divide in various plane of division.

2. Mycoplasmas are classified as low G+C gram positive bacteria in textbook. It is due to the fact that it belong to the family of gram positive group of bacteria known as Fermicutes which have lost their cell wall during evolution or Mycoplasmas are evolved due to degenerative evolution of gram positive bacteria group. Mycoplasmas share common evolutionary history with the group which include low guanine and cytosine content than adenine and thymine in their DNA. They doesn't even have cell wall. Gram positive bacteria stain purple on the account of staining which helps in determining the peptidoglycan cell wall. Since Mycoplasma lacks the cell wall and appear as gram negative bacteria during staining.

3. Dichotomous key to distinguish among the orders of Gammaproteobacteria.

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