Judul: Cultivation and characterization of active compound and nutrients of marine microalgae Chaetoceros gracilis
Abstrak: Chaetoceros gracilis is a genera of marine microalgae that can be found in Indonesian waters. The aims of this research were: 1) to grow Chaetoceros gracilis in NPSi medium and to get the extract of Chaetoceros gracilis which contained antibacterial compound, 2) to investigate activity and stability of Chaetoceros gracilis extract, 3) to investigate the effect of Chaetoceros gracilis extract against bacteria, and 4) to determine the chemical composition of Chaetoceros gracilis biomass. The Chaetoceros gracilis was grown in nitrogen phosphate silica (NPSi) medium, continously aerated and illuminated by a 20 watt tube lamp (2500 lux). The cultivation was maintained at 25-26 oC, and harvested on the 7th day of cultivation. The biomass was separated using ceramic filter pore 0,3 μm and then freezed dried. They were extracted by methanol. Antibacterial activity of extract was tested against Gram positive and negative bacteria by agar diffusion method, compared to commercial antibiotic (chloramphenicol, tetracycline, oxytetracycline and ampicillin). The stability was tested during storage. Mechanism of inhibition was determined by analyzing cell damage. The content of Chaetoceros gracilis biomass such as amino acid, fatty acid, and minerals was determined using HPLC, GC and AAS respectively. The result showed that Chaetoceros gracilis grew well in NPSi medium. Extract of Chaetoceros gracilis showed antibacterial activity against Vibrio harveyi, Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 25923, dan Bacillus cereus ATCC 13091 at the concentration of 300 μg/disc. Antibacterial activity of Chaetoceros gracilis extract at concentration of 300 μg/disc was lower than antibacterial at the same concentration of chloramphenicol, tetracycline, oxytetracycline and ampicillin. After being storaged for 6 months, the extract still showed the same antibacterial activity. The extract of C. gracilis cause damage by leakage of the cell. Chaetoceros gracilis contained essential amino acids (threonine, valine, methionine, leucine, isoleucine, lysine, phenylalanine, histidine), and non essential amino acids (aspartic acid, glutamic acid, serine, glycine, arginine, alanine, tyrosine); saturated fatty acid such as caprilic acid, (C8:0), myristic acid, (C14:0), palmitic acid (C16:0), lauric acid, (C12:0), pentadecanoic acid, (C15:0), stearic acid (C18:0), arachidic acid, (C20:0), heneicosanoic acid (C21:0), behenic (C22:0), and unsaturated fatty acid such as palmitoleic acid (C16:1), heptadecanoic acid (C17:1), myristoleic acid (C14:1), pentadecanoic acid (C15:1), oleic acid (C18:1n9), linoleic acid (C18:3n3), arachidonic acid (C20:4n6), g-linolenic acid (C18:3n6), docosadienoic acid (C22:2), eicosapentaenoic acid (C20:5n3) and docosahexaenoic acid (C22:6n3). Biomass of Chaetoceros gracilis contained minerals such as phosphor (P), magnesium (Mg), ferrum (Fe), zink (Zn), calcium (Ca), and silicate. The biomass also containted alcalloid, steroid, carbohydrate, amino acid, and 0,1 % nucleic acid. It need further study on toxicity.
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Judul: Ektraksi senyawa antibakteri dari mikroalga laut jenis chaetoceros gracilis dan uji aktivitasnya terhadap beberapa bakteri
Abstrak: Penelitian terhadap Chaetoceros gracilis, salah satu jenis mikroalga yang dominan pada perairan lepas pantai Indonesia, bertujuan untuk menentukan pola pertumbuhan mikroalga tersebut pada suliu ruang, mengekstrak senyawa antibakterinya, dan menguji aktivitas antibakteri tersebut terhadap beberapa bakteri. C. gracilis dikultivasi dalam medium Guillard pada suhu ruang dengan kepadatan awal l,0xl0⁴ sel/ml, pengaturan aerasi, dan pemberian cahaya sebesar 1500 luks dari lampu TL 20 watt. Penentuan pola pertumbuhan dilakukan dengan metode hitungan langsung di bawah mikroskop, mengkonversi nilai kepadatannya ke dalam log, dan memplotkannya pada milimeter blok sehingga diperolah kurva pertumbuhan. Ekstraksi senyawa antibakteri ekstraseluler dan intraseluler dilakukan dengan memodifikasi prosedur umum dari metode Quinn (1988) dan Pratt (1945). Setelah diperoleh ekstrak kasar intraseluler dan ekstraseluler antibakteri, dilakukan uji aktivitasnya terhadap bakteri Gram negatif (E. coli dan Pseudomonas sp.) dan Gram positif (B. subtilis dan S. aureus) dengan memodifikasi metode Caliberated Dichotomous Sensitivity (CDS) test. Antibiotik streptomycin dan aquadest steril digunakan sebagai kontrol positif dan negatif.
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Judul: Pemodelan Nilai Tukar Rupiah Terhadap US Dollar Menggunakan Deret  Waktu Hidden Markov Dua Waktu Sebelumnya
Abstrak: Nilai tukar Rupiah terhadap US Dollar mengalami perubahan setiap waktunya dalam periode yang panjang dan perubahan yang terjadi mungkin terjadi kembali di masa mendatang. Jika penyebab kejadiannya tidak diamati secara langsung dan membentuk suatu rantai Markov maka perubahan nilai tukar Rupiah dapat dimodelkan dengan model deret waktu hidden Markov. Untuk menggambarkan perilaku nilai tukar Rupiah terhadap US Dollar, dalam karya ilmiah ini digunakan model deret waktu hidden Markov dua waktu sebelumnya. Model ini mengasumsikan bahwa nilai tukar Rupiah terhadap US Dollar bergantung pada rantai Markov yang merupakan penyebab kejadian yang tidak diamati dan nilai tukar Rupiah dua waktu sebelumnya.
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