Azolla for the circular economy
Research profile Henriette: https://orcid.org/0000-0001-6171-3029
Please see also: https://www.azollahs.com
For a movie on the Azolla project click the following Link
Since 2013, we research promising novel crops suited to the needs of a circular economy, in particular the fern/cyanobacterium symbioses from the genus Azolla. Azolla ferns fix both CO2 and N2 and grow at high rates. We determined their yield potential at 50 t dry weight biomass per ha annually in a continuous harvesting process; the biomass contained some 20% w/w protein.
Their use as a bio-fertilizer is ancient yet they were never domesticated, possibly because they are not seed plants: the life cycle of Azolla ferns is characterized by a diploid sporophyte afloat on the water surface; upon transition to sexual reproduction sporophytes form micro- and megasporocarps which are then shed; the microsporocarp disintegrates releasing massulae which contain microspores and attach to megaspores by way of their glochidia. In the ditch sediment, the flagellate male gametes released from the massulae fertilize the egg cells in the archaegonia of the megagametophyte inside the megasporocarps, initiating sporeling development; as the sporeling (young sporophyte) grows, it displaces the megasporocarp indusium cap and its shoot apical meristem gets infected by the symbiotic filamentous cyanobacteria, the Nostoc azollae. N. azollae are maintained in all shoot apices of the sporophytes from where they are dispatched into forming leaf cavities of the leaf initials, and in reproductive organ initials. Once inside the leaf cavities N. azollae differentiate heterocysts at high rates and fixate N2 at rates that cover the nitrogen needs of the symbiosis even at its highest growth rates.
We established cryopreservation, crossing and sporeling germination protocols for reliable storage of Azolla filliculoides and its cyanosymbiont. We currently investigate the induction of the sexual reproduction in this heterosporous fern, aiming to control dissemination in all Azolla species. Sexual reproduction in A. filiucloides could be reliably induced with far-red light which allowed simultaneous profiling of pro and eukaryote RNA (Dual RNAseq) and therefore an initial characterization of the developmental transition.
Our recent publications explore diverse subjects related to Azolla domestication: sexual reproduction (Brouwer et al., 2014; Dijkhuizen et al., 2020), productivity and independence from N2 fertilizer (Brouwer et al., 2017), suitability of Azolla lipids as fuels and specialty chemicals (Brouwer et al, 2015), protein yields in simple processing schemes, polyphenol content and biosynthesis pathways (Brouwer PhD Thesis 2017; Brouwer 2018, 2019) and the Azolla metagenome (Dijkhuizen et al., 2018) as part of a larger effort to sequence and assemble a first fern reference genome of good quality (Li et al., 2010).
We are further looking into ways to genetically modify Azolla and its symbionts. Any help with this would be greatly appreciated to open up Azolla as a model system for research on questions related to
1) the evolution of the fern lineage, a sister lineage to seed plants with some 12 k species,
2) the symbiotic cross-talk with Nostoc cyanobacteria that permit such a high dinitrogen fixing rates and productivity of Azolla fern species without nitrogen fertilizer,
3) adaptations required for colonization of the water surface,
4) molecular breeding and agro-system development.
The Azolla Project in Utrecht has enjoyed the help from many collaborators in the Netherlands and abroad. We thank in particular:
Dr. Klaas G. Nierop (Utrecht University, Netherlands); Dr. Adrie van der Werf (Wageningen Research, Netherlands); Dr. Ingrid van der Meer (Wageningen Research, Netherlands). Prof. Fons Smolders (B-WARE/Radboud University, Netherlands); Dr. Henk Bolhuis (Royal Netherlands Institute for Sea Research-NIOZ, The Netherlands); Prof. Andrea Bräutigam (Bielefeld University, Germany); Prof. Andreas Weber (Heinrich Heine University Düsseldorf, Germany); Prof. Kathleen Pryer (Duke University, USA); Dr. Fay-Wei Li (Boyce Thompson Institute, USA; Dr. Josh P. Der (California State University Fullerton, USA); Prof. Sandra Nierzwicki-Bauer (Rensselaer Polytechnic Institute, USA); Prof. Peter Lindblad (Uppsala University, Sweden).