IPTEK The Journal for Technology and Science, Vol. 30(3), December. 2019. 2088-2033 (pISSN: 0853-4098) 101 Study of UV-B Mutation Effect on pH Resistance and Lipid Production of Microalgae Botryococcus braunii Thea Prastiwi Soedarmodjo, Fanina Aulia Rachma, Hakun Wirawasista Aparamarta, and Arief Widjaja AbstractMicroalgae Botryococcus braunii is a potential biodiesel producer as an alternative for fossil fuels due to its high lipid content. UV-B mutations were carried out to see the effect in microalgae growth at various pHs (3-8). Reduction of nitrogen levels was carried out to see the effect on the growth and lipid production of microalgae. UV-B mutation increased the ability of growth and resistance of B. braunii against low pH. Under low nitrogen conditions, the growth of B. braunii cells would not continue for a longer time. B. braunii which grow in nitrogen depletion medium produced lipid content greater than normal nitrogen. UV-B light mutation also increased the lipid content of B. braunii. At 7 days of incubation, the mutation not only increased lipid content, but also significantly increased the triacylglycerols (TAG) content of B. braunii lipids. KeywordsMicroalgae, Botryococcus braunii, Nitrogen Depletion, pH, mutation, UV-B. I. INTRODUCTION 1 nergy is now an absolute necessity and must be fulfilled. Almost all facilities and infrastructure supporting human life are driven by energy. Until now, energy as driving force of the human economy is still supplied by fossil fuel. Fossil energy is limited and less environmentally friendly. The combustion process produces unfavorable effects on the environment and health as greenhouse effects, due to the content of carbon dioxide (CO 2 ), Sulphur dioxide (SO 2 ), and nitrogen oxides (NO x ) [1]. Indonesia has been widely known as a maritime country. Two-thirds of its territory is ocean with a 108,000 km coastline [2]. One living thing that grows and thrives in the ocean is algae. Microalgae are one of the producers of oil or lipid as a potential biodiesel feedstock. Microalgae use solar energy and carbon dioxide to produce biomass. Microalgae cells grow in water media that is why microalgae have a high level of efficiency in terms of the use of water, carbon dioxide, and other nutrients [3]. Microalgae have advantages over other oil-producing plants such as jatropha, sunflowers, or palm oil for land growth is not competing with conventional agricultural land, has a very high growth rate and has a better lipid composition as biodiesel feedstock [4]. Some of the common problems encountered in microalgae cultivation as a producer of lipid relate to its resistance to changes in pH. CO 2 is a carbon source for microalgae while the addition of CO 2 will reduce its pH value due to the reaction with H 2 O produce HCO 3 - [5]. Algae are diverse group of photosynthetic organisms ranging from unicellular (microalgae) to multicellular (macro algae) forms. They have chlorophyll as primary photosynthetic pigment and do not have a common ancestor. Commonly, algae population falls under two broad categories, (1) microalgae: microscopic algae that grows in fresh water and marine environment and (2) Thea Prastiwi Soedarmodjo, Fanina Aulia Rachma, Hakun Wirawasista Aparamarta, and Arief Widjaja are Departement of Chemical Engineering, Institut Teknologi Sepuluh Nopember, Surabaya, 60111, Indonesia. E-mail: arief_w@chem-eng.its.ac.id. macro algae: comparatively large, multicellular organisms that grows in marine environment. Microalgae are microscopic, unicellular and phototropic organisms that fall under three categories, namely Diatoms (Bacillariophyceae), Green algae (Chlorophyceae) and Golden algae (Chrysophyceae). Diatoms are the dominant life forms in phytoplankton and probably represent the largest group of biomass producers on earth. Green algae are abundantly found in fresh water than in marine water. Golden algae are similar to diatoms and produce oils and carbohydrates. Microalgae are efficient producers of lipids and other great metabolites that work by utilizing nutrients in the presence of solar energy [6]. One of the microalgae that can be processed into biodiesel is Botryococcus braunii. Microalgae B. braunii are a single-cell green microalga from the Chlorophyceae class that live in freshwater to marine water [1]. B. braunii is one of microalgae with the largest lipid contain, 25-75% dry weight [4]. It contains 41.1% free fatty acids, 2.1% triacylglycerols, 1.8% diacylglycerols, and 1.7% monoacylglycerols [7]. Types of fatty acids found in B. braunii lipids dominated by oleic and palmitic acid [8]. Biodiesel is a mixture of alkali ether and fatty acids obtained from the transesterification process of vegetable or animal oils. Diesel raw materials are hydrocarbons which contain 8-10 carbon atoms per molecule while hydrocarbons contained in vegetable oils on average are 16-20 carbon atoms per molecule so that vegetable oils have a higher viscosity and low combustion as fuel [1]. Through esterification and transesterification process, microalgae lipid can be converted into biodiesel [8]. Mutation in microorganisms is carried out to improve its nature. Research using UV-B mutagen show that irradiated microbes with UV-B ray at the right dose will produce higher activity than native ones. UV radiation will cause changes in gene composition as mutant genes that can cause certain enhancement in microorganisms [9]. Microalgae as one of microorganisms are often investigated for its influence on UV-B radiation. Skerratt et. al. (1998), examined the effect of UV-B ray mutations on the lipid content of Antarctic marine phytoplankton microorganisms. It was found that lipid levels per cell E