Multiplication

Bacteria (unlike viruses) can reproduce independently. This is achieved by a simple asexual division, usually by transverse division, budding or budding. The two newly formed cells then each grow into a full-fledged bacterium.

However, since this multiplication is asexual, i.e. two clones identical to the previously existing bacterium are always created, bacteria must use other mechanisms to achieve gene transfer. A distinction is made here between three forms. On the one hand there is conjugation, which is especially used by Gram-negative bacteria (see below).

This type is used by bacteria that possess so-called “sexpili”. These proteins can be used to form a bridge between two bacteria, through which DNA can be transferred directly from one bacterium to the other. Gram-positive bacteria tend to practice transduction, a method in which the bacteria make use of certain viruses, the bacteriophages.

These take up bacterial DNA and then pass it on to another bacterium. However, this transformation, which can only be found very rarely, is based on the direct uptake of naked DNA. Bacteria can be classified according to different aspects.

1: On the basis of their external shape (morphology). On the one hand there are spherical bacteria, the cocci. These can either be present individually or clustered together.

Most frequently, cocci are found in large numbers clustered together like grapes (staphylococci), arranged in a long row (streptococci) or in pairs of two (diplococci, e.g. gonocococci). More rarely, cocci also occur once in groups of four (tetrad) or eight (sarcines). In addition to the cocci, there are also the rods.

These bacteria are elongated or cylindrical or clumsy (coccoid) and have rounded, pointed or rectangular ends. The helical bacteria or spirals (e.g. the spirochetes) can be identified under the microscope thanks to their many clearly visible coils. Lastly, there are the filamentous bacteria such as streptomycetes.

2: In addition, the bacteria can be distinguished by their staining behaviour. The so-called Gram staining is used for this purpose. In this method, the bacteria are first treated with a blue dye, which is then washed out with an alcohol preparation.

Bacteria that do not succeed in doing so have a thick cell wall in which the blue dye has practically settled. These now blue bacteria are called Gram-positive. After the decolouration with alcohol another, this time a red, dye is used.

The bacteria without a cell wall, from which the blue dye was previously washed out, now stain red and are called Gram-negative. 3: In addition, the different bacteria also show different behaviour towards oxygen. Some bacteria can only exist in the presence of oxygen, as they need it for consumption.

These bacteria are called aerobic bacteria or aerobic beers. The opposite is the case with the so-called anaerobic bacteria or anaerobes, which can only survive in an oxygen-free environment. In between are the facultative anaerobes.

These facultative anaerobic bacteria do not need oxygen, but they can tolerate it (there is another subgroup here, namely the microaerophilic bacteria, which prefer a very low concentration of oxygen in their environment). 4: Last but not least, the different types of bacteria can be classified according to their endowment with goats (flagella). Some bacteria have no flagella at all, some have only one flagellum (they are monotrich), others have exactly two flagella at opposite poles (amphitrich), several flagellums but only at one pole of the cell (lophotrich) and others are occupied by flagella all around (peritrich).

These spores are resistant permanent forms of the bacteria, which can be formed under poor living conditions to ensure survival. Spores reduce their metabolism to the bare minimum, enabling them to withstand extreme conditions such as heat or cold, drought, radiation, chemicals or food shortages. As soon as the external conditions become more friendly again, the spores can transform back into their normal, “active” bacterial form.