Lichen | EPFL Graph Search

A lichen (ˈlaɪkən , UKalsoˈlɪtʃən ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship. Lichens are important actors in nutrient cycling and act as producers which many higher trophic feeders feed on, such as reindeer, gastropods, nematodes, mites, and springtails. Lichens have properties different from those of their component organisms. They come in many colors, sizes, and forms and are sometimes plant-like, but are not plants. They may have tiny, leafless branches (fruticose); flat leaf-like structures (foliose); grow crust-like, adhering tightly to a surface (substrate) like a thick coat of paint (crustose); have a powder-like appearance (leprose); or other growth forms. A macrolichen is a lichen that is either bush-like or leafy; all other lichens are termed microlichens. Here, "macro" and "micro" do not refer to size, but to the growth fo

Harvesting of Chlorella sorokiniana by co-culture with the filamentous fungus Isaria fumosorosea: A potential sustainable feedstock for hydrothermal gasification

Christof Holliger, Stephen Mackay, Eduardo Pereira Gomes, Jean-Paul Schwitzguebel

Despite recent advances in down-stream processing, production of microalgae remains substantially limited because of economical reasons. Harvesting and dewatering are the most energy-intensive processing steps in their production and contribute 20–30% of total operational cost. Bio-flocculation of microalgae by co-cultivation with filamentous fungi relies on the development of large structures that facilitate cost effective harvesting. A yet unknown filamentous fungus was isolated as a contaminant from a microalgal culture and identified as Isaria fumosorosea. Blastospores production was optimized in minimal medium and the development of pellets, possibly lichens, was followed when co-cultured with Chlorella sorokiniana under strict autotrophic conditions. Stable pellets (1–2 mm) formed rapidly at pH 7–8, clearing the medium of free algal cells. Biomass was harvested with large inexpensive filters, generating wet slurry suitable for hydrothermal gasification. Nutrient rich brine from the aqueous phase of hydrothermal gasification supported growth of the fungus and may increase the process sustainability.

Elsevier2015

Pelletization of micro-algae by induced lichen formation through co-culture with filamentous fungi

Christof Holliger, Stephen Mackay, Eduardo Pereira Gomes, Pierre Rossi, Jean-Paul Schwitzguebel

The use of micro-algae within industrial applications, such as biofuel production, has several limitations with regard to cost and therefore sustainability. Micro-algae biomass consists of small single cells that stay in suspension making them difficult to harvest, requiring filtration or pelletization methods which contribute to a significant cost of the total biomass production. Recent studies have investigated the use of co-cultivation of fungi and algae to form symbiotic lichen communities as a mechanism of harvesting the micro-algae biomass. Lichens are symbiotic community structures comprised of fungal mycobionts and algal photobionts. Algae, inoculated with fungal biomass are rapidly absorbed from suspension by the mycobiont to form a pellet structure. Pelletization has several beneficial effects for industrial application due with regard to biomass and efficient harvesting by size exclusion. Additional benefits include the application towards agricultural and hydrothermal waste water, where both algal and fungal cultures are have been used for bio-remediation of waste water. The application of the lichen formation in would be to increase biomass, bio-remediate wastewater as well as potentially extract valuable by-products such as carotenoids. In this study, three commercially interesting algal species Chlorella vulgaris, Chlorella sorokiniana and Scenedesmus vacuolatus were investigated for their compatibility with a previously uncharacterized Sordariomycete to form a symbiotic lichen structure. Optimal culture conditions, photobiont-mycobiont interaction and biomass composition were investigated for application in industry.

2013

Microalgae for wastewater treatment, CO2 mitigation and biofuels : dream or sustainable maid for all work?

Christof Holliger, Stephen Mackay, Eduardo Pereira Gomes, Jean-Paul Schwitzguebel

Over the last decade, intensive research has been carried out all over the world to explore the huge potential of microalgae for biofuel production, which could be coupled to the use of industrial flue gas to enhance CO2 fixation as a greenhouse gas mitigation strategy and to remove pollutants from various wastewaters. However, large-scale microalgae production for such purposes is not yet technically and economically feasible. Challenges are thus to increase the efficiency of both algae production and conversion into biofuel. The following parameters are critical for sustainable microalgal biomass cultivation: CO2 concentration; possible use of wastewater streams; light intensity and quality; photobioreactor design; batch, fed-batch or continuous growth conditions. The objective of our research was thus to assess the influence of these parameters on the quantitative and qualitative production of biomass, lipids and added-value chemicals, taking into account the probable antagonism between biomass and lipid production, often depending on the nitrogen supply. Several microalgal species were grown at laboratory scale to compare the yield of biomass and lipid production. In addition to the potential use of oil for biodiesel production, we are currently working towards demonstrating the technical feasibility of an innovative process, for syngas production via hydrothermal processing of microalgae. The process is envisioned as a closed-cycle with respects to nutrients, water and CO2, that are separated and reused for microalgae growth. The possible effect of increasing injection of CO2 in the growth medium was also investigated, with the aim to recycle CO2 from flue gas and enhance biomass production. On the other hand, to achieve the economical and ecological sustainability of algal biofuel production, it will be necessary to integrate it with the extraction of high-value products in a biorefinery process. Carotenoids have been proposed as added-value compounds that could contribute to make microalgal biofuel production economically feasible. Therefore, the viability and sustainability of extracting carotenoids before the hydrothermal treatment of the remaining biomass to produce syngas were investigated. Finally, harvesting and dewatering microalgae cells remains a technical challenge and typically contributes to 20-30% of biomass production costs and can represent up to half of the total cost of algal biofuels. The potential of co-culture of filamentous fungal species with microalgae in a lichenization process as a strategy to reduce the cost and energy consumption of harvesting and of the whole process seems promising and was thus investigated. In submerged cultures, filamentous microorganisms actually aggregate and grow as loosely packed pellets or compact granules. Microalgae cells were immobilized in these pellets and easily removed as an aggregate with the fungal cells. Pellet formation is strain specific and highly dependent on operational conditions during cultivation. This study was especially focused on lichen pellet formation during the co-culture of Chlorella sorokiniana and of an unidentified filamentous fungus, which was eventually characterized. While algae growth was optimal between pH 6 and 10, the highest pellet formation was observed in the pH range of 4-7, thus requiring a strict control of pH during the whole cultivation. The dense formed pellets did sediment in submerged cultures when the agitation was stopped and were easily harvested. The effect of such a co-cultivation on the production of added-value chemicals like carotenoids and on the biofuel potential of the remaining biomass is under evaluation, and will be compared to results obtained with cultivation of microalgae only. The proposed strategies may significantly reduce energy demands with regards to harvesting and dewatering of microalgal biomass and improve the sustainability of the whole process, but should be assessed at larger scale. Acknowledgements: The research was supported by the Swiss Secretariat for Education, Research and Innovation, in the framework of COST Action CM0903 (Utilisation of biomass for sustainable fuels and chemicals).

2014