Judul: Isolated Populations of Nitrifying and Denitrifying Bacteria in Seagrass Ecosystems on Pramuka Island, Jakarta
Abstrak: Bakteri mengambil peran penting pada ekosistem lamun, salah satu contohnya peran bakteri nitrifikasi dan denitrifikasi yang berperan dalam siklus nitrogen pada ekosistem lamun. Nitrogen adalah nutrien esensial yang sangat dibutuhkan oleh tanaman dan organisme hidup lainnya. Tujuan penelitian ini untuk mengisolasi bakteri asosiasi sedimen lamun yang berperan dalam siklus nitrifikasi dan denitrifikasi di ekosistem lamun Pulau Pramuka, Kepulauan Seribu, Jakarta. Penelitian yang dilakukan meliputi isolasi bakteri menggunakan media spesifik nitrifikasi dan denitrifikasi dari sampel sedimen lamun, karakterisasi bakteri secara morfologi koloni, bentuk sel dan pewarnaan Gram, uji oksidatif/fermentatif, katalase, oksidase, selulase, motilitas, serta dilakukan pengukuran kualitas perairan, kualitas sedimen, dan komposisi lamun. Jenis lamun yang ditemukan pada lokasi pengamatan yaitu, Thalassia hemprichii, Cymodocea rotundata, Halophila ovalis, dan Enhalus acoroides. Jenis lamun Thalassia hemprichii mendominasi pada kedua Stasiun penelitian. Isolat bakteri yang berhasil diisolasi menggunakan media spesifik nitrifikasi berjumlah 16 isolat dan isolat bakteri yang berhasil diisolasi menggunakan media denitrifikasi berjumlah 23 isolat. Karakteristik isolat bakteri pada kedua Stasiun penelitian didominasi tepian licin, bentuk bundar, elevasi cembung, pigmen putih, dan dominan masuk kedalam golongan Gram negatif dengan bentuk basil. Uji oksidatif mendapatkan hasil 8 isolat oksidatif, oksidase positif ditemukan pada 29 isolat, pengujian katalase ditemukan 39 isolat positif, dan uji motilitas positif pada bakteri jenis nitrifikasi dan negatif pada bakteri jenis denitrifikasi. Hasil dari uji terhadap seluruh isolat selanjutnya dilakukan identifikasi dan memperoleh hasil 5 genus bakteri yaitu, Pseudomonas, Corynebacterium, Achromobacter, Moraxella, dan Brucella. Jumlah isolat bakteri yang terisolasi dikaitkan dengan kerapatan lamun perjenis dengan menggunakan analisis Pearson Correlation yang menunjukkan hasil adanya hubungan isolat bakteri terhadap kerapatan jenis lamun, Bacteria play an important role in seagrass ecosystems, one example being the role of nitrifying and denitrifying bacteria in the nitrogen cycle of seagrass ecosystems. Nitrogen is an essential nutrien required by plants and other living organisms. The objective of this research is to isolate sediment-associated bacteria that play a role in the nitrification and denitrification cycles in the seagrass ecosystem of Pramuka Island, Thousand Islands, Jakarta. The research includes isolating bacteria using specific nitrification and denitrification media from seagrass sediment samples, characterizing bacteria based on colony morphology, cell shape and Gram staining, oxidative/fermentative tests, catalase, oxidase, cellulase, motility, as well as measuring water quality, sediment quality, and seagrass composition. The seagrass species found at the observation site are Thalassia hemprichii, Cymodocea rotundata, Halophila ovalis, and Enhalus acoroides. Thalassia hemprichii dominates at both research stations. A total of 16 bacterial isolates were successfully isolated using specific nitrification media, and 23 bacterial isolates were successfully isolated using denitrification media. The characteristics of the bacterial isolates at both research stations are predominantly smooth edges, round shape, convex elevation, white pigment, and predominantly fall into the Gram-negative group with bacillus shape. The oxidative test resulted in 8 oxidative isolates, positive oxidase was found in 29 isolates, catalase testing showed 39 positive isolates, and motility test was positive for nitrifying bacteria and negative for denitrifying bacteria. Further identification of all isolates resulted in the discovery of 5 bacterial genera: Pseudomonas, Corynebacterium, Achromobacter, Moraxella, and Brucella. The number of isolated bacteria is associated with the density of seagrass
Keyword: bacteria, denitrification, nitrification, seagrass, sediment

Judul: Laju Peluruhan Bakteri Fosfat oleh  Bakteri Sedimen Pada Ekosistem Lamun di Pulau Pramuka, Kepulauan Seribu, DKI Jakarta
Abstrak: Lamun (seagrass) adalah tumbuhan tingkat tinggi berbunga yang dapat tumbuh dengan baik pada lingkungan laut dangkal. Pertumbuhan lamun dipengaruhi oleh beberapa faktor salah satunya nutrien yaitu fosfat. Fosfat di sedimen biasanya tidak bisa digunakan langsung oleh lamun dikarenakan terikat dengan mineral lain sehingga dibutuhkan organisme lain untuk membantu mineralisasi fosfat di alam dan salah satunya adalah bakteri. Penelitian dilakukan untuk mengisolasi bakteri peluruh fosfat pada sedimen serta mengetahui pengaruh laju peluruhan fosfat terhadap kerapatan lamun yang berada di Pulau Pramuka. Hasil isolasi bakteri peluruhan fosfat menggunakan media Pikovskaya diperoleh 28 isolat. Hubungan antara bakteri peluruh fosfat dengan kerapatan lamun dilakukan menggunakan analisis persen korelasi, uji one way ANOVA, regresi linier sederhana serta uji fisiologis untuk mengetahui genus dari bakteri peluruh fosfat. Hasil uji menunjukkan bahwa pengaruh peluruhan fosfat oleh bakteri dengan kerapatan lamun memiliki keterikatan sebesar 16% dan 14%. Korelasi jenis lamun Thallasia hemprichii dan Enhalus acoroides memiliki nilai korelasi yang rendah sementara Cymodocea rotundata serta Halophila ovalis memiliki korelasi kuat. Hasil uji fisiologis diketahui bakteri termasuk dalam genus Pseudomonas dan Actenobacter., Seagrass is a flowering higher plant that can grow well in shallow marine environments. Seagrass growth is influenced by several factors, one of which is nutrients, namely phosphate. Phosphate in sediments usually cannot be used directly by seagrasses because it is bound with other minerals so that other organisms are needed to help mineralize phosphate in nature and one of them is bacteria. The research was conducted to isolate phosphate-degrading bacteria in the sediment and determine the effect of phosphate decay rate on seagrass density in Pramuka Island. The results of isolation of phosphate decay bacteria using pikovskaya media obtained 28 isolates. The relationship between phosphate decay bacteria and seagrass density was carried out using percent correlation analysis, One Way ANOVA test, Simple linear regression, and physiological test to determine. the genus of phosphate decay bacteria. The test results show that the effect of phosphate decay by bacteria with seagrass density has an attachment of 16% and 14%. The correlation of seagrass species Thallasia hemprichii and Enhalus acoroides has a low correlation value while Cymodocea rotundata and Halophila ovalis have a strong correlation. The results of physiological tests showed that the bacteria belonged to the genus psedumonas and actenobacter.
Keyword: Actenobacter, phosphate, phosphate decaying bacteria, physiological, Pseudumonas, seagrass

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: