Penicillium isolation from citrus fruit

Natural product discovery is such an attractive field because it offers someone the chance to discover a new compound, not yet known to science, with potentially life saving medicinal properties.  Even most non-scientists will know about penicillin, its use as an antibiotic during World War II, and the numerous lives it has saved since then.  There are guaranteed to be many as yet undiscovered antimicrobial or antifungal compounds out there somewhere in nature, and our goal is to one day be able to find them.  The process of identifying and purifying an unknown compound can be a daunting task, so to gain experience, we’ve decided to start with isolating a well known compound.

The basic goals are to isolate a Penicillium strain, culture it, do a liquid/liquid extraction to try to isolate penicillin, then do disc diffusion assays and check for rings of inhibition.  If all goes well and we can get a really pure sample with some separation techniques, it’d be great to run an NMR or LC-MS and see if we could elucidate its structure, pretending it was an “unknown new bio-active compound”.

The lemon piece may have been sampled too late, as the normally olive green Pencillium strain was replaced and covered with vegetative white mycelia.  Time will tell if it is a different species or not.




Above are some pictures taken at different stages of the experiment.  The lemon covered in white is the end of the experiment, the olive green was half way through.  The microscope pictures were taken from the olive green mold sample, and show Penicillium’s tell-tale fan shaped conidia.

Read more about Penicillium at


Below are some videos of me finally transferring some samples into liquid growth flasks, aka plastic coffee cups, to see if we can get more growth, perhaps of a semi-pure culture – and the secondary metabolites of said strain.



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  1. […] is an update post on the quest to isolate a Penicillium strain from citrus fruit, in the hopes of at some point along the journey finding some penicillin. […]

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