Vampirovibrio chlorellavorus (Gromov et Mamkaeva, 1980) is a member of the phylum cyanobacteria that has been described as an obligate pathogen of several of the green microalga, Chlorella. It utilizes as yet unknown functions to access the contents of individual Chlorella sp. host cells, which results in cell death. Its presence in a cultivated Chlorella sorokiniana culture was first discovered using polymerase chain reaction (PCR) to amplify the 16S ribosomal DNA gene, followed by DNA sequencing. Its continued routine detection throughout much of the cultivation season suggested it was an endemic member of the phycosphere community in this open cultivation system, located in Tucson, Arizona. Ultimately, its presence resulted in rapid death of C. sorokiniana in open pond systems and reduced biomass harvest. PCR analysis of total DNA isolated from sand and soil layers removed from a nearby riverbed indicated that V. chlorellavorus resides naturally in the riverbed. The ability to manage this bacterial pathogen in cultivated Chlorella host species is hindered by the limited information available in the literature regarding the biological and genomic characteristics of V. chlorellavorus. The objective of this study was to identify environmental factors that trigger the apparent increased growth rate of V. chlorellavorus and rapid algal death during the cultivation cycle. In laboratory experiments, V. chlorellavorus was shown to cause death of C. sorokiniana when the temperature exceeded 28°C, whereas, algal death was not observed when the temperature was 24°C or lower, among the temperatures tested. Also, the bacterium was more pathogenic to C. sorokiniana, grown in open cultivation systems during the summer months, compared to the cooler season months. Futhermore, when C. sorokiniana and V. chlorellavorus were co-cultivated in the presence of sodium chloride ranging from 0-10 g per liter, the growth of the bacterium was not impeded to any extent that might suggest C. sorokiniana was rendered less susceptibility to pathogen attack. Future work involves examining more triggers and ways to inhibit V. chlorellavorus growth.

Unicellular microalgae are a renewable bioresource that can meet the challenge forfood and energy in a growing world population. Using sunlight, CO2, nutrients,and water, algal cells produce biomass in the form of sugars, proteins and oils, allof which carry commercial value as food, feed and bioenergy. Flue gas CO2 andwastewater nutrients are inexpensive sources of carbon and fertilizers. Microalgaecan mitigate CO2 emissions and reduce nutrients from waste streams whileproducing valuable biomass.My focus was on some of the challenging aspects of cultivating microalgae ascrop: the response of biomass production and quality to seasonality, nutrients andbiological interactions. Approach spans from laboratory experiments to large-scaleoutdoor cultivation, using single microalgal strains and natural communities insouthern (Portugal) and northern (Sweden) Europe.Half of the seasonal variation in algal oil content was due to changes in light andtemperature in outdoor large-scale cultures of a commercial strain (Nannochloropsisoculata). Seasonal changes also influence algal oil composition with more neutrallipids stored in cells during high light and temperature. Nitrogen (N) stress usuallyenhances lipid storage but suppresses biomass production. Our manipulationshowed that N stress produced more lipids while retaining biomass. Thus,projecting annual biomass and oil yields requires accounting for both seasonalchanges and N stress to optimize lipid production in commercial applications.Baltic Sea microalgae proved to be a potential biological solution to reduce CO2emissions from cement flue gas with valuable biomass production. A multi-speciescultivation approach rather than single-species revealed that natural or constructedcommunities of microalgae can produce equivalent biomass quality. Diversecommunities of microalgae can offer resilience and stability due to more efficientresource utilization with less risk of contamination, less work and cost for culturemaintenance.Stable algal biomass production (annual basis) was achieved in outdoor pilot-scale(1600 L) cultivation of Baltic Sea natural communities using cement flue gas as aCO2 source. Results indicate favorable algal oil content at northern Europeanlatitudes compared to southern European latitudes.My thesis establishes the potential of cultivating microalgae as a bioresource inScandinavia, and using a community approach may be one step towardssustainable algal technology.

Ulva intestinalis är en fotoautotrof grönalg som är utspridd i stora delar av världen och har ett flertal användningsområden, däribland som matråvara samt som biobränsle. Matindustrin står idag för en fjärdedel av världens utsläpp av växthusgaser. För att FN:s globala mål ska uppnås innan år 2030 måste dessa utsläpp minska. Ett sätt att bidra till att målen nås är att ändra vilka livsmedel som produceras, där alger kan vara en del av den framtida mera hållbara maten. Syftet Med detta arbete var att undersöka möjligheterna för en hållbar algodling för matkonsumtion.Målet var att genom en litteraturstudie hitta en parameter som potentiellt kan påverka tillväxten av Ulva intestinalis och planera ett experiment i en odlingsanläggning på norra Öland som undersöker den valda parametern. I litteraturstudien undersöktes det vilken parameter som skulle kunna testas i en framtida odlingsanläggning. Resultatet som erhölls från litteraturstudien var att substrat är viktigt för algens sporsättning och i kombination med projektets begränsande faktorer blev substrat den parameter som bör testas i experimentet. Utifrån att substrat valdes som parameter lades ett förslag på ett experiment fram. Slutligen diskuterades potentiella felkällor samt så gavs det förslag på eventuella fortsatta studier. / Ulva intestinalis is a photoautotroph green algae that is found in large parts of the world, and has a variety of uses, for example as food and as biofuel. The food industry is responsible for one fourth of the world’s green gas emissions, and for the United Nations’ Sustainable Development Goals to be reached before the year 2030, these emissions must be reduced. One way to contribute to the achievement of these goals is to change what kind of food is being produced,and algae could be part of the more sustainable future food. The purpose with the project was to examine the possibilities for a sustainable land-based algal cultivation for food use. The goal was to find a parameter that could potentially influence the growth of Ulva intestinalis, and to plan an experiment in a cultivation plant in northern Öland that examines the selected parameter. The method that was selected to fulfill the goal of the project was a literature study, in which some potential growth parameters were identified, so a conclusion of which parameter should be tested in a future experiment could be made. The result from the study was that substratum is important for the settlement of the spores, and in combination with the limits of the project it was chosen to be the parameter to be tested in the planned experiment. On the basis of substratum as the selected parameter, a proposal for an experiment was presented. Finally, potential sources of error were discussed, and suggestions for future studies were made.