Penicillin Fermentation- Microorganisms

Penicillin was active against Gram positive bacteria, Nocardia, and Actinomycetes, but not against most Gram negative bacteria. It interferes with cell wall synthesis of actively growing sensitive organisms. It mainly inhibits the cross linking steps of peptidoglycan synthesis in the cell wall.

Structure of Penicillin

Penicillin is a group of compounds having common basic nucleus, 6-amino penicillanic acid (6-APA).  6-APA contains two rings- β-lactam &semithiazolidine ring.

                               

Penicillin F (2-pentenyl penicillin) was the original Penicillin obtained in more amount with P. notatum. Later, when P. chrysogenum was isolated and employed in fermentation, Penicillin K was obtained majorly along with dihydropenicillin F in the fermentation broth. With the addition of Corn steep liquor (CSL) as precursor, Penicillin G or benzyl penicillin was the major product in the mixture. It had better pharmacological properties and better stability.  

Thus penicillin is a group of compounds and the major compound depends on the microorganism and the media employed for fermentation.

Penicillins are of two different types,

i Natural Penicillin

ii Synthetic Penicillin

Natural penicillin is directly harvested from the Penicillium mold (P. notatum or P. Chrysogenum). 

Synthetic penicillin consists of the basic Penicillin nucleus (6-APA), but with new side chains that change properties of natural penicillin. Eg., Ampicillin, Methicillin, Penicillin V, etc.  These Penicillins could be produced by fermentation (biosynthetic) or chemical treatment (semi-synthetic).

Penicillin Fermentation -Microorganisms

Penicillium species are used in the Penicillin fermentation- P. notatum & P. chrysogenum.

P. notatum was used initially in stationary mat culture, however the strain was highly unstable and the yield variable. Stationary fermentation was replaced by submerged fermentation methods and P. notatum was found unsuitable.

    

                        P. chrysogenum                                     P. notatum

In 1943, P. chrysogenum was isolated from moldy fruit and was found as a high yielding strain and better suited for submerged fermentation. Descendants of P. chrysogenum is now widely used as production strain.

Strain development methods such as mutagenesis (x-ray/uv/alkylating agents, nitrosoguanidine), genetic recombination, protoplast fusion technique were employed to obtain high yielding variety- - P. chrysogenum NRRl 1951 Wis Q176 strain.

Fleming’s isolate, P. notatum gave a yield of around 2 IU/ml whereas P. chrysogenum NRRl 1951 WIS Q176 strain and its descendants yielded around > 85000 IU/ml after strain improvement. Such is the power of strain improvement techniques.

After strain improvement the production strains are carefully maintained by different preservation techniques like,

1. A spore suspension may be mixed with a sterile, finely separated inert support like soil or sand and then desiccated.

2. The spore suspension can be stored under liquid nitrogen (-196°C) i.e. in a frozen state.

3. The spore suspension can be lyophilized in appropriate media.

Along with improved yield, other properties were also modified, such as pigment production. P. chrysogenum produced yellow water soluble pigment which gave a yellow tint to the final preparations. With mutation and selection, strains that do not produce the pigment but produced penicillin in high yields could be selected.