Judul: Phosphate-solubilizing Activity of  Actinobacteria Isolated from Soil and Plant as Endophytes
Abstrak: Aktinobakteri memiliki kemampuan meningkatkan ketersediaan fosfat di tanah yang tersedia untuk tanaman melalui mekanisme pelarutan dan mineralisasi fosfat. Aktinobakteri dari beragam kondisi lingkungan telah diisolasi dan dikoleksi di Laboratorium Mikrobiologi IPB, namun belum diketahui kemampuannya dalam melarutkan fosfat. Penelitian ini bertujuan mengkarakterisasi dan menguji aktivitas pelarutan fosfat isolat aktinobakteri asal tanah dan endofit tanaman. Tahapan penelitian meliputi, pengujian aktivitas pelarutan fosfat secara kualitatif dan kuantitatif pada periode inkubasi 7, 10, dan 14 hari pada media Pikovskaya yang mengandung trikalsium fosfat, pengukuran pH filtrat kultur, penapisan potensi isolat serta karakterisasi morfologi koloni isolat terpilih. Sembilan isolat aktinobakteri mempunyai aktivitas pelarutan fosfat yang beragam. Uji kualitatif menunjukkan nilai IPF terbesar dimiliki XGS 4. Hasil uji konsentrasi fosfat anorganik terlarut oleh XGS 7 lebih tinggi dibandingkan XGS 4 yang memiliki nilai IPF lebih besar. Filtrat kultur mengalami penurunan pH dari netral ke arah masam (4-5). Empat isolat terpilih memiliki karakteristik morfologi yang mirip genus Streptomyces. Studi ini menunjukkan aktinobakteri asal tanah dan endofit tanaman memiliki kemampuan melarutkan fosfat anorganik., Actinobacteria can increase the availability of phosphorus (P) in the soil through phosphate solubilizing and mineralization activities, and the available P will be absorbed by the plants. Actinobacteria have been isolated from various environments and collected in Microbiology Laboratory IPB, but their capability in solubilizing phosphate is still unknown. This study aimed to characterize and examine the phosphate-solubilization activity of actinobacteria isolated from soil and plant as endophytes. The activity of actinobacteria in solubilizing-phosphate was measured both qualitatively and quantitatively. Phosphate solubilization assay was conducted after incubation periods of 7, 10, and 14 days on Pikovskaya media containing tricalcium phosphate. To predict the mechanism of phosphate solubilization, the pH of the culture filtrate was measured throughout the experiment. Morphological characterization was conducted for the selected isolates. Various phosphate solubilization activities were found for the nine actinobacteria isolates examined. Qualitative tests revealed that XGS 4 had the highest IPF values. Meanwhile, based on dissolved inorganic phosphate concentration, XGS 7 showed to have higher activity than XGS 4 which was previously known to have a greater IPF value. Over the period of incubation, the pH of the culture has changed from neutral to acidic (4-5). The four selected isolates had morphological characteristics similar to the Streptomyces genus. This study shows that actinobacteria from soil and plant as endophytes can solubilize inorganic phosphate.
Keyword: organic acid, inorganic phosphatase, Streptomyces, tricalcium phosphate

Judul: Morphological Characterization and Ability of Actinobacteria as Nitrogen Fixer In Vitro
Abstrak: Aktinobakteri ditemukan hidup sebagai endofit dan rizosfer berpotensi sebagai pemacu tumbuh tanaman. Nitrogen merupakan unsur utama yang diperlukan tanaman untuk pertumbuhannya. Informasi tentang aktinobakteri penambat N2 masih jarang dilaporkan, sedangkan keberadaan aktinobakteri di lingkungan sangat banyak. Penelitian ini bertujuan mengkarakterisasi morfologi aktinobakteri endofit dan rizosfer serta mengkaji kemampuannya dalam menambat N2 secara in-vitro. Tahapan penelitian meliputi peremajaan isolat aktinobakteri, karakterisasi morfologi, pertumbuhan pada media bebas nitrogen, uji produksi amonia, serta pola produksi amonia. Delapan isolat aktinobakteri asal endofit dan rizosfer dikarakterisasi secara makroskopis dan mikroskopis berdasarkan morfologi koloni, penataan rantai spora, warna miselium aerial dan substrat pada empat media berbeda. Hasil karakterisasi morfologi menunjukkan delapan isolat yang diamati memiliki kedekatan dengan Streptomyces spp.. Delapan isolat aktinobakteri mampu menambat N2 berdasarkan pertumbuhan pada media bebas nitrogen dan menghasilkan amonia berkisar antara 4,851 ± 0,100 - 9,474 ± 0,136 ppm. Tiga isolat diantaranya menghasilkan amonia paling baik berasal dari endofit tanaman padi, yaitu IPBCC.b.14.1531, IPBCC.b.14.1534, dan IPBCC.b.14.1535 dengan amonia sebesar 9,474 ppm; 8,587 ppm; dan 6,083 ppm. Pola produksi amonia ketiga isolat terus meningkat seiring makin lamanya masa inkubasi dengan amonia paling tinggi dihasilkan pada hari ke-15. Tiga isolat aktinobakteri tersebut berpotensi menjadi PGPB yang dapat dikembangkan sebagai bakteri pemacu tumbuh tanaman. Kata kunci: aktinobakteri, amonia, morfologi koloni, Streptomyces., Endophytic and rhizosphere actinobacteria have the potential to promote plant growth. Nitrogen is the main element needed by plants for growth. Information about N2-fixing actinobacteria still rarely reported, while the presence of actinobacteria in environment is abundant. This study aimed to characterize the morphology of endophytic and rhizosphere actinobacteria and to study their ability to fix N2 in vitro. The research stages included rejuvenation of isolates, morphological characterization, growth on nitrogen-free media, ammonia-production test and patterns. Eight actinobacteria isolates origin were characterized macroscopically and microscopically based on colony morphology, spore chain arrangement, aerial and substrate mycelium color on four different media. The results of morphological characterization showed that eight isolates observed were close to Streptomyces spp.. Eight isolates were able to fix N2 based on growth on nitrogen-free media and produced ammonia in range of 4.851±0.100 - 9.474±0.136 ppm. The three best ammonia-producing isolates from rice plant endophytes, namely IPBCC.b.14.1531, IPBCC.b.14.1534, and IPBCC.b.14.1535 with ammonia level i.e. 9.474; 8,587; 6.083 ppm respectively. The ammonia production pattern of three isolates continued to increase along with the longer incubation period and the highest ammonia produced on the 15th day. Three isolates have potential to become PGPB which can be developed further as plant growth-promoting bacteria. Keywords: actinobacteria, ammonia, colony morphology, Streptomyces.
Keyword: actinobacteria, ammonia, colony morphology, 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.
Keyword: