Physiology of aquatic microorganisms from the perspective of bioprocess development

Industrial biotechnology is gradually transforming the landscape of chemical production. The driving force that promotes the application of industrial biotechnology includes the increasing concerns of climate change and sustainability of chemical production. Microorganisms and enzymes, as the key catalysts of industrial biotechnology, have been increasingly examined for their suitability in bioprocesses. Currently, most industrial microbial strains have terrestrial origin. Aquatic microorganisms, though believed to be tremendously diverse, have not been extensively used by the existing bioprocesses. One reason is that the physiology of most aquatic microorganisms has not been investigated from the perspective of bioprocess development. Aiming to bring more aquatic microorganisms to industrial application, by improving the physiological understanding of them, case studies were conducted, characterising eight diverse aquatic microorganisms at different readiness levels of bioprocess development. Neutral lipid production from a green alga, Chlorella protothecoides, was analysed in various levels of nitrogen limiting conditions. The result found that nitrogen limitation, which triggers lipid accumulation, can be achieved in continuous cultivations with constant nitrogen feed. C. protothecoides conducts photosynthesis to maximise the utilisation of available light in mixotrophic conditions. This makes it suitable for stable continuous mixotrophic cultivations for lipid production. Another photosynthetic aquatic microorganism, Euglena gracilis was studied in more detail interms of cell composition in response to cultivation conditions. The confirmed cellular composition of E. gracilis makes it ideal material for whole cell utilisation as food or feed. Six marine fungi were characterised for hydrolytic activities. Their abilities of hydrolysing several polymers usually found in macroalgae were confirmed. This suggest the existence of enzymes with unique substrate specificity in some of these marine fungi. Marine fungi produce novel compounds of various bioactivities beyond hydrolytic enzymes. The production of an antibacterial macrocyclic polyester, calcaride-A, from Calcarisporium sp. was characterised. A preliminary cultivation process was developed that can produce enough calcaride-A material for further bioactivity research. The case studies demonstrated that physiological characterisation from the perspective of bioprocess development is crucial for bioprocess development. Though this is not unique to aquatic microorganisms, expanding the physiological characterisation of aquatic microorganisms will hopefully attract more investment to the utilisation of aquatic microorganism.