eng Oriental Scientific Publishing Company Biosciences Biotechnology Research Asia 0973-1245 2016-03-31 13 1 109 114 10.13005/bbra/2011 6659 article Eko Agus Suyono 1 Sri Nopitasari 1 Muhammad Zusron 1 Pretty Khoirunnisa 1 Dinda Ayu Islami 1 Cakra Buana Prabeswara 1 Laboratory of Biotechnology, Faculty of Biology, Universit as Gadjah Mada Jl. Teknika Selatan, Sekip Utara, Yogyakarta, Indonesia 55281 Microalgae is one organism that can be used as raw material for bioethanol production. Growth and composition of microalgae cells affected by strain and environmental conditions, including temperature, pH and nutrients. Nutrients are used for the growth of one of silica, except that the silica used to form frustule on diatoms. This study aimed to determine the effect of silica on growth, dry weight, and carbohydrate produced from mixed cultures Phaeodactylum sp. and Chlorella sp. Cultivation is carried out for 21 days on a laboratory scale using a medium F / 2. Culture growth was measured by counting cell density. The dry weight is calculated every 7 days to obtain a biomass productivity. Carbohydrate content was measured by the phenol-sulfuric method. samples were taken on days 0, 7, 14 and 21. It could be concluded that the highest quota of carbohydrate per cell was obtained on Si 90 ppm, accounted for 0.03977 mg / cell. Furthermore, total carbohydrate content and the highest percentage in the mixed culture Phaeodactylum sp. and Chlorella sp. were found in treatment of 30 ppm and 6 ppm,  amount of  289.93 mg / L and 40.45%, respectively. Thus the mixed culture was prospective as bioethanol feed stock. https://www.biotech-asia.org/vol13no1/effect-of-silica-on-carbohydrate-content-of-mixed-culture-phaeodactylum-sp-and-chlorella-sp/ mixed culture; Phaeodactylum sp.; Chlorella sp.; carbohydrate; bioethanol