L. johnsonii is a bacterium belonging to the family of lactobacillaceae. Next to nearly 500 other microbial species it is part of the human intestinal flora which is located in the gastro-intestinal tract. L. johnsonii, like all lactobacilli, is gram-positive, anaerobic and has a rod-like shape without spore formation. It’s main aid for the human body is to digest polysaccharides and proteins. Apart from this, L. johnsonii is capable of producing short-fatty acids and vitamins, that can make up to 15% of the human caloric intake. Due to its capability to undergo fermentation, it also provides help in preserving food, such as cheese, milk and vegetables, by producing lactic acid. We choose L. johnsonii as part of the “acidophilus complex” for our project, because it helps the human body in a probiotic way and is capable of undergoing certain transformations.
Pathology and Application in Biotechnology
L. johnsonii is part of the human intestinal tract. Therefore it is not known to have a pathogenic effect in humans. It is mostly known to work in a probiotic way. Apart from some cases, where patients had previous diseases, there are no known pathogenic effects caused by any lactobacilli strain.
There are many possible ways lactobacilli can be used due to its capability to undergo fermentation and the production of acid. First, L. johnsonii can be used to preserve fresh food, i.e. dairy products, meat and vegetables. Second, L. johnsonii can be used directly as a probiotic, cultivated for example in yoghurt. This can be seen in the human stomach, where L. johnsonii has a regulating effect on Helicobacter pylori, which resides in the gastrum. Apart from the human body, L. johnsonii is used in poultry industry by reducing diseases caused by Escherichia coli. This can significantly reduce the usage of antibiotics.
L. johnsonii in our project
In our project we used the Lactobacillus johnsonii strain ATCC33200, purchased from DSMZ (Deutsche Sammlung von Microorganismen und Zellkulturen), because this strain is certified for its harmlessness. Handling Lactobacillus johnsonii in lab, however, was very difficult. Firstly, L. johnsonii didn’t grow very well on MRS plates. Therefore liquid cultures and glycerol stocks were mainly used for cultivation. Secondly, growth was not reliable and if grown, bacteria left log phase after 6 hours of incubation at 37°C and died rather quickly. For this reason, passaging and transformation experiments were only possible during a small window of time in the log-phase, not afterwards.