Image analysis supported moss cell disruption in photo-bioreactors

Process Engineering of Biopharmaceutical Production in Moss Bioreactors via Model-Based Description and Evaluation of Phytohormone Impact

The moss Physcomitrella is an interesting production host for recombinant biopharmaceuticals. Here we produced MFHR1, a synthetic complement regulator which has been proposed for the treatment of diseases associated to the complement system as part of human innate immunity. We studied the impact of different operation modes for the production process in 5 L stirred-tank photobioreactors. The total amount of recombinant protein was doubled by using fed-batch or batch compared to semi-continuous operation, although the maximum specific productivity (mg MFHR1/g FW) increased just by 35%. We proposed an unstructured kinetic model which fits accurately with the experimental data in batch and semi-continuous operation under autotrophic conditions with 2% CO₂ enrichment. The model is able to predict recombinant protein production, nitrate uptake and biomass growth, which is useful for process control and optimization. We investigated strategies to further increase MFHR1 production. While mixotrophic and heterotrophic conditions decreased the MFHR1-specific productivity compared to autotrophic conditions, addition of the phytohormone auxin (NAA, 10 µM) to the medium enhanced it by 470% in shaken flasks and up to 230% and 260%, in batch and fed-batch bioreactors, respectively. Supporting this finding, the auxin-synthesis inhibitor L-kynurenine (100 µM) decreased MFHR1 production significantly by 110% and 580% at day 7 and 18, respectively. Expression analysis revealed that the MFHR1 transgene, driven by the Physcomitrella actin5 (PpAct5) promoter, was upregulated 16 h after NAA addition and remained enhanced over the whole process, whereas the auxin-responsive gene PpIAA1A was upregulated within the first 2 hours, indicating that the effect of auxin on PpAct5 promoter-driven expression is indirect. Furthermore, the day of NAA supplementation was crucial, leading to an up to 8-fold increase of MFHR1-specific productivity (0.82 mg MFHR1/g fresh weight, 150 mg accumulated over 7 days) compared to the productivity reported previously. Our findings are likely to be applicable to other plant-based expression systems to increase biopharmaceutical production and yields.

Life at the boundary: photosynthesis at the soil-fluid interface. A synthesis focusing on mosses

Mosses are among the earliest branching embryophytes and probably originated not later than the early Ordovician when atmospheric CO2 was higher and O2 was lower than today. The C3 biochemistry and physiology of their photosynthesis suggests, by analogy with tracheophytes, that growth of extant bryophytes in high CO2 approximating Ordovician values would increase the growth rate. This occurs for many mosses, including Physcomitrella patens in suspension culture, although recently published transcriptomic data on this species at high CO2 and present-day CO2 show down-regulation of the transcription of several genes related to photosynthesis. It would be useful if transcriptomic (and proteomic) data comparing growth conditions are linked to measurements of growth and physiology on the same, or parallel, cultures. Mosses (like later-originating embryophytes) have been subject to changes in bulk atmospheric CO2 and O2 throughout their existence, with evidence, albeit limited, for positive selection of moss Rubisco. Extant mosses are subject to a large range of CO2 and O2 concentrations in their immediate environments, especially aquatic mosses, and mosses are particularly influenced by CO2 generated by, and O2 consumed by, soil chemoorganotrophy from organic C produced by tracheophytes (if present) and bryophytes.

The potential of Physcomitrella patens as a platform for the production of plant-based vaccines

The moss Physcomitrella patens has a number of advantages for the production of biopharmaceuticals, including: i) availability of standardized conditions for cultivation in bioreactors; ii) not being part of the food chain; iii) high biosafety; iv) availability of highly efficient transformation methods; v) a haploid, fully sequenced genome providing genetic stability and uniform expression; vi) efficient gene targeting at the nuclear level allows for the generation of mutants with specific post-translational modifications (e.g., glycosylation patterns); and vii) oral formulations are a viable approach as no toxic effects are attributed to ingestion of this moss. In the light of this panorama, this opinion paper analyzes the possibilities of using P. patens for the production of oral vaccines and presents some specific cases where its use may represent significant progress in the field of plant-based vaccine development. The advantages represented by putative adjuvant effects of endogenous secondary metabolites and producing specific glycosylation patterns are highlighted.

Reannotation and extended community resources for the genome of the non-seed plant Physcomitrella patens provide insights into the evolution of plant gene structures and functions

Background

The moss Physcomitrella patens as a model species provides an important reference for early-diverging lineages of plants and the release of the genome in 2008 opened the doors to genome-wide studies. The usability of a reference genome greatly depends on the quality of the annotation and the availability of centralized community resources. Therefore, in the light of accumulating evidence for missing genes, fragmentary gene structures, false annotations and a low rate of functional annotations on the original release, we decided to improve the moss genome annotation.

Results

Here, we report the complete moss genome re-annotation (designated V1.6) incorporating the increased transcript availability from a multitude of developmental stages and tissue types. We demonstrate the utility of the improved P. patens genome annotation for comparative genomics and new extensions to the cosmoss.org resource as a central repository for this plant “flagship” genome. The structural annotation of 32,275 protein-coding genes results in 8387 additional loci including 1456 loci with known protein domains or homologs in Plantae. This is the first release to include information on transcript isoforms, suggesting alternative splicing events for at least 10.8% of the loci. Furthermore, this release now also provides information on non-protein-coding loci. Functional annotations were improved regarding quality and coverage, resulting in 58% annotated loci (previously: 41%) that comprise also 7200 additional loci with GO annotations. Access and manual curation of the functional and structural genome annotation is provided via the http://www.cosmoss.org model organism database.

Conclusions

Comparative analysis of gene structure evolution along the green plant lineage provides novel insights, such as a comparatively high number of loci with 5’-UTR introns in the moss. Comparative analysis of functional annotations reveals expansions of moss house-keeping and metabolic genes and further possibly adaptive, lineage-specific expansions and gains including at least 13% orphan genes.

Glycoprotein production in moss bioreactors

Complex multimeric recombinant proteins such as therapeutic antibodies require a eukaryotic expression system. Transgenic plants may serve as promising alternatives to the currently favored mammalian cell lines or hybridomas. In contrast to prokaryotic systems, posttranslational modifications of plant and human proteins resemble each other largely, among those, protein N-glycosylation of the complex type. However, a few plant-specific sugar residues may cause immune reactions in humans, representing an obstacle for the broad use of plant-based systems as biopharmaceutical production hosts. The moss Physcomitrella patens represents a flexible tissue-culture system for the contained production and secretion of recombinant biopharmaceuticals in photobioreactors. The recent synthesis of therapeutic proteins as a scFv antibody fragment or the large and heavily modified complement regulator factor H demonstrate the versatility of this expression system. A uniquely efficient gene targeting mechanism can be employed to precisely engineer the glycosylation machinery for recombinant products. In this way, P. patens lines with non-immunogenic optimized glycan structures were created. Therapeutic antibodies produced in these strains exhibited antibody-dependent cellular cytotoxicity superior to the same molecules synthesized in mammalian cell lines.

Moss bioreactors producing improved biopharmaceuticals

Plants may serve as superior production systems for complex recombinant pharmaceuticals. Current strategies for improving plant-based systems include the development of large-scale production facilities as well as the optimisation of protein modifications. While post-translational modifications of plant proteins generally resemble those of mammalian proteins, certain plant-specific protein-linked sugars are immunogenic in humans, a fact that restricts the use of plants in biopharmaceutical production so far. The moss Physcomitrella patens was developed as a contained tissue culture system for recombinant protein production in photo-bioreactors. By targeted gene replacements, moss strains were created with non-immunogenic humanised glycan patterns. These were proven to be superior to currently used mammalian cell lines in producing antibodies with enhanced effectiveness.