Judul: The Growth of Actinobacteria at Various Concentrations of Iron and Their Ability to Produce Plant Growth Promoting Compounds
Abstrak: Lahan pasang surut merupakan daerah yang mendapatkan pengaruh langsung atau tidak langsung oleh pasang surut air laut di sekitarnya. Permasalahan pada proses pengelolaan lahan pasang surut berupa kandungan besi dan logam Al yang tinggi, pH rendah dan salinitas tinggi. Aktinobakteri mampu menghasilkan senyawa pemacu tumbuh tanaman dan hidup pada kandungan besi tinggi. Penelitian ini bertujuan menguji kemampuan tumbuh aktinobakteri dengan kode isolat Cal31t, Dbi28t, Crc32t dan Cal24h pada berbagai konsentrasi besi dan sebagai penghasil IAA serta penambat nitrogen. Pengamatan morfologi koloni untuk konfirmasi dilakukan setelah isolat ditumbuhkan pada medium ISP4. Pertumbuhan isolat pada kondisi cekaman dilakukan dengan menumbuhkannya di medium ISP2 pada pH 4, NaCl 3%, AlCl3 750 mg.L-1 dan FeCl3 0, 500, 1000, 2000, 4000, 8000, 16000, 32000 mg.L-1. Morfologi isolat menunjukkan kemiripan dengan Streptomyces. Keempat isolat mampu tumbuh hingga konsentrasi FeCl3 32.000 mg.L-1 dengan kemampuan tumbuh bervariasi. Isolat Cal31t dan Dbi28t memiliki berat kering miselium lebih tinggi dibandingkan Crc32t dan Cal24h. Produksi IAA dari keempat isolat terdeteksi hingga konsentrasi FeCl3 4.000 mg.L-1. Keempat isolat mampu tumbuh pada medium bebas N serta memproduksi amonia. Crc32t mampu menghasilkan amonia sebanyak 0,354 mg.L-1. Berdasarkan hasil penelitian, isolat Cal31t dan Crc32t berpotensi dikembangkan sebagai bakteri pemacu tumbuh tanaman pada lahan pasang surut., Tidal land is an area which directly or indirectly affected by the tides. Problems in tidal land cultivation process include high iron and Al content, low pH and high salinity. Actinobacteria can produce plant growth promoting compounds and live at high iron content. This study aimed to test the growth ability of actinobacteria, i.e. Cal31t, Dbi28t, Crc32t and Cal24h at various concentrations of iron, IAA producer, and nitrogen fixing. Confirmation for colony morphology were observed after grown on ISP4 medium. The growth of isolates under stress conditions were determined by cultivating them in ISP2 medium at pH 4, 3% NaCl, AlCl3 750 mg.L-1 and 8 concentrations of FeCl3 0, 500, 1000, 2000, 4000, 8000, 16000, 32000 mg.L-1. Morphology of isolates showed similiarities to Streptomyces. Isolates were able to grow up to FeCl3 32.000 mg.L-1 with varying growth abilities. Cal31t and Dbi28t had higher dry weight mycelium than Crc32t and Cal24h. IAA production still detected up to 4.000 mg.L-1 of FeCl3 concentrations. Isolates were also able to grow on N-free medium and produced ammonia. Crc32t produced ammonia as much as 0,354 mg.L-1. Based on the result, Cal31t and Crc32t have potential to be further developed as plant growth promoting bacteria in tidal fields.
Keyword: bobot kering miselium, konsentrasi besi, penambat nitrogen, produksi IAA

Judul: Formulasi Aktinomiset Rizosfer Pemacu Tumbuh dengan Menggunakan Bahan Pembawa Gambut
Abstrak: Aktinomiset yang hidup di sekitar perakaran (rizosfer) merupakan salah satu kelompok bakteri Gram-positif yang dapat berperan penting sebagai agen pemacu pertumbuhan tanaman atau Plant Growth Promoting Rhizobacteria (PGPR). Penelitian ini bertujuan memformulasi aktinomiset rizosfer pemacu tumbuh menggunakan bahan pembawa berupa gambut, serta mengetahui kemampuannya dalam memproduksi IAA, melarutkan fosfat, dan tumbuh pada media bebas nitrogen. Pengamatan morfologi isolat ARJ 16, ARJ 28, ARJ 32, dan ARJ 34 memperlihatkan keragaman warna miselium aerial dan tipe miselium yang sama, yaitu spiral. Berdasarkan pengamatan tersebut keempat isolat termasuk ke dalam genus Streptomyces. Keempat isolat tersebut mampu tumbuh pada medium bebas nitrogen (N-free medium) yang ditandai dengan tumbuhnya koloni aktinomiset pada media tersebut. Isolat-isolat tersebut juga mampu melarutkan fosfat dengan indeks pelarutan fosfat tertinggi ditunjukkan oleh isolat ARJ 34. Berdasarkan uji secara kolorimetri, keempat isolat diketahui mampu menghasilkan IAA dengan konsentrasi tertinggi yaitu 30,43 ppm yang ditunjukkan oleh isolat ARJ 28, dan konsentrasi terendah yaitu 21,93 ppm yang ditunjukkan oleh isolat ARJ 16. Identifikasi isolat aktinomiset berdasarkan gen 16S rRNA menyatakan bahwa keempat isolat tersebut termasuk ke dalam genus Streptomyces. Keempat Streptomyces tersebut telah berhasil diformulasi menggunakan bahan pembawa utama yaitu gambut. Streptomyces di dalam bahan pembawa mampu mempertahankan viabilitas selnya sebesar 108 CFU g-1 setelah masa penyimpanan selama lima minggu pada suhu ruang., Actinomycetes that live in the area around roots (rhizosphere) are a group of Gram-positive bacteria that can play an important role as plant growth promoters or Plant Growth Promoting Rhizobacteria (PGPR). This study aims to formulate growth-promoting rhizosphere actinomycetes using peat as a carrier, and to determine their ability to produce IAA, solubilizing phosphate, and grow on nitrogen-free media. Morphology of isolates ARJ 16, ARJ 28, ARJ 32, and ARJ 34 varied in color diversity of aerial mycelia and the same type of mycelium, namely spiral. Based on the four isolates included in the genus Streptomyces. The four isolates were able to grow on nitrogen-free medium which was characterized by the growth of actinomycete colonies on the media. These isolates were also able to solubilize phosphate with the highest phosphate solvent index shown by isolate ARJ 34. Based on colorimetric tests, all four were known to be able to produce IAA with the highest concentration of 30.43 ppm indicated by isolate ARJ 28, and the lowest concentration of 21 93 ppm indicated by ARJ 16 isolate. The identification of actinomycete isolates based on the 16S rRNA gene stated that the four isolates belonged to the genus Streptomyces. The four Streptomyces were successfully formulated using the main carrier material, namely peat. Streptomyces in the carrier material was able to maintain cell viability of 108 CFU g-1 after five weeks of storage at room temperature.
Keyword: IAA, phosphate solubilization, PGPR, Streptomyces

Judul: Truncated Stop Loss as a Optimal Solution of Reinsurance Agreement in One-Period Model
Abstrak: Reinsurance is one of risk management efforts of an insurance company, which is called the cedent. Similar with insurance, reinsurance constitutes the cedent to pay the premium. We consider one-period reinsurance model and derive a rule which minimizes the ruin probability of the cedent for a fixed reinsurance premium. Therefore, it is needed to construct an optimal reinsurance agreement for the cedent. The premium is calculated according to four different principles, i.e. economic, generalized zero-utility, Esscher, and mean-variance principles. Stop loss is a reinsurance contract which protect the insurance company for losses that exceed a certain amount. The result of this research shows that a truncated stop loss is an optimal agreement in the class of all reinsurance contracts with various premiums calculated using above mentioned principles.
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