Ulva growth, development and applications

Ghaderiardakani, Fatemeh (2019). Ulva growth, development and applications. University of Birmingham. Ph.D.

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Abstract

The green marine macroalgae Ulva (Ulvophyceae) are common algae distributed worldwide, which play a key role in aquatic ecosystems. Ulva species are a potentially valuable resource for food, feed, fertiliser and fuel but can also cause massive nuisance blooms if they grow unchecked.
For correct growth and development, Ulva requires the presence of a combination of regulatory morphogenetic compounds released by associated epiphytic bacteria in addition to nutritional parameters. The first results chapter examines the extent of specificity or generality of bacteria-induced morphogenesis in Ulva, by cross-testing bacteria isolated from several Ulva species on Ulva mutabilis and Ulva intestinalis. We show that pairs of bacterial strains isolated from Ulva species can fully rescue U. mutabilis or U. intestinalis morphology.
In the second results chapter, activity of algal growth- and morphogenesis-promoting factors (AGPFs) derived from bacteria were estimated in a land-based integrated multitrophic aquaculture system (IMTA) of fish and macroalgae (located at the coastal lagoon Ria de Aveiro, Portugal), using a standardised bioassay with axenic cultures of Ulva. Nutrient availability was also assessed in this IMTA system. The study thus informs aspects of the various potential aquaculture-environment interactions. It was observed that both the water from the lagoon (external to the farm system) and the water from the fish pond (input for algae cultures) could completely restore the normal growth and morphology of the macroalga under axenic conditions. The results highlight the presence of a sufficient chemical cocktail of AGPFs in this IMTA system required for growth and morphogenesis of Ulva. In addition, the water of fish farming increases the nutrient availability (nitrate and ammonium) needed for macroalgae production. The conclusion of this chapter is that Ulva´s sustainable growth and development can benefit from multitrophic aquaculture systems and shallow water systems, due to the naturally enriched AGPFs and their in-situ production by bacteria in intensive algal aquacultures.
In the final results chapter, the effects of U. intestinalis extracts on germination and root development in the model land plant Arabidopsis thaliana were examined. Ulva extract concentrations above 0.1% inhibited Arabidopsis germination and root growth. Ulva extract <0.1% stimulated root growth. All concentrations of Ulva extract inhibited lateral root formation. An abscisic-acid insensitive mutant showed altered sensitivity to germination- and root growth-inhibition. Ethylene- and cytokinin-insensitive mutants were partly insensitive to germination-inhibition. This suggests that different mechanisms mediate each effect of Ulva extract on early Arabidopsis development and that multiple hormones contribute to germination-inhibition.
Taken together, the results of this thesis highlight: (i) Specific Ulva-associated bacterial functions (promoting cell division, or cell differentiation) that cannot be assigned to a specific genus/taxonomic group of bacteria, (ii) an IMTA system ensuring an adequate supply of nutrients and a sufficient chemical mixture of AGPFs for reliable Ulva cultivation and (iii) the first-characterised mechanisms to date by which Ulva extract can impact germination and growth in Arabidopsis.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):