Moss bioreactor



A moss bioreactor is a photobioreactor used for cultivation and breeding of mosses. Usually it is used for the production of recombinant protein using transgenic moss. This biotechnological process is also referred to as Molecular farming.

Being very frugal, photoautotrophic organisms, mosses have already been kept in vitro for research purposes since the beginning of the 20th century.

In order to come up to safety standards regarding the handling of genetically modified organisms and to gain sufficient biomass for experimental purposes, the first moss bioreactors for the model organism Physcomitrella patens were developed by Ralf Reski in the 1990s.

Functional Principle
The underlying principle of a moss bioreactor is the one of a suspension culture. The moss is cultivated in liquid, agitated and aerated medium. The culture is kept under lighting with temperature and pH-value held constant. The culture medium – often a minimal medium – contains all nutrients and dietary minerals needed for growth of the moss.

To ensure a maximum increase in biomass, the moss is kept at the protonema-stage by continuous mechanical disruption, using e. g. rotating blades. . Once the density of the culture has reached a certain threshold, differentiation of the protonema to “adult moss plants” is caused by a lack of nutrients and the increasing content of phytohormones in the medium. At this point in time, if the culture is intended for further use, it has to be diluted strongly with fresh medium.

According to the intended yield, this functional principle can be realised by various types and sizes of bioreactors. The cultivation chamber can, for example, consist of a column, a tube or even exchangeable plastic bags.

Production of Biopharmaceuticals
Various biopharmaceuticals have already been produced using moss bioreactors. Ideally, the recombinant protein of interest can be purified from the medium directly. One example for this production method is factor H: this molecule is part of the human complement system. Defects in the corresponding gene are associated with human diseases such as severe kidney and retinal disorders. Biologically active recombinant factor H was produced in a moss bioreactor for the first time in 2011.