Judul: Diversity of Bacterial Community that Contribute in Nitrogen Cycle at Lake of Situ Sawangan-Bojongsari, West Java.
Abstrak: One of the problems in freshwater management is the declining of water quality due to pollution of nitrogen compound. Mechanisms of nitrogen transformation by indigenous bacteria in water body have been considered to solve this problem. Situ Sawangan-Bojongsari is the largest lake at Depok city, West Java. Antrophogenic activities on the lake have been accused to cause nitrogen pollution. Accordingly, the aim of this research is to investigate the abundance and diversity of bacterial community that contribute in N cycle as well as to study the profile of physical and chemical parameters that influence the bacterial community. Water and sediment samples were collected from three sampling station, each with three replicate. Water samples were collected from the surface of the water column (0 cm), secchi depth (110) and the bottom (230 cm). Sediment samples were collected by sediment core and divided to three section depth (0-2 cm, 2-5 cm, and 5-10 cm). Analysis of physical factors was fermormed at the time of sampling which included temperature, pH, and DO. Wheter analysis of chemical factors from water and pore water sediment covered some parameters: TN, TOM, DOM, TOC, N-NH3, N-NO3, dan N-NO2. Analysis of the bacterial abundance that contribute in N cycle was done using MPN method. The community structure of the bacteria was analyzed using DGGE method. Amplification product of nifH, amoA, and nosZ gene were targeted for DGGE analysis. The most abundance of nitrogen fixing bacteria was found at the sediment in the depth of 2-5 cm (4.43 log cell/mL) and the less abundance was found at the water coloumn in the depth of 0 cm (2.46 log cell/mL). The most abundance of ammonia oxidizing bacteria was found in the depth of 0 cm (270 cell/mL). The less abundance of the bacteria was found in the depth of 230 cm (73 cells/Ml). The most abundance of nitrite oxidizing bacteria was found at the water column in the depth of 0 cm (2.87 log cell/mL) and the less abundance of the bacteria was found in the depth of 230 cm. There was no ammonia and nitrite oxidizing bacteria found in the sediment. The most abundance of nitrate reducing bacteria (denitrification) was found at the sediment in the depth of 2-5 and 5-10 cm (6.04 log cell/mL) and the less abundance of the bacteria was found at the water column in the depth of 0 cm (1.32 log cell/mL). The most abundance of nitrate reducing bacteria (DNRA) was found at the sedimen in the depth of 5-10 cm (4.32 log cell/ml) and the less abundance of the bacteria was found at the water column in the depth of 0 and 110 cm (1.56 log cell/mL). The most abundance of amonifying bacteria was found at the sediment in the depth of 5-10 cm (4.43 log cell/mL) and the less abundance of the bacteria was found at the water column in the depth of 0 cm (1.86 cell/mL). A total of 11 unique bands of nifH gene generated after DGGE analysis. Six of eleven unique bands of the gene selected, sequenced and identified by searching
Keyword: DGGE, nifH, amoA, nosZ

Judul: Keragaman Komunitas Bakteri Pemfiksasi Nitrogen pada Tanah Sawah di Sukabumi
Abstrak: Dinitrogenase is an important enzyme in nitrogen fixation. The enzyme has 2 sub unit proteins, Fe Protein and MoFe protein, each encoded by nifH and nifD. DGGE is one of metagenomic analysis technique that can represent the abundance of specieses in environment, based on melting behavior of amplicones in linearly increasing denaturant in polyacrylamide gel. The aim of this research was to assay diversity of nitrogen fixing-bacteria on rice field. The soil samples of rice field treated with inorganic fertilizer NPK 15:15:15 250 kg/ha (100% dosage) (K), biofertilizer and NPK 62.5 kg/ha (25% dosage) (C), and NPK only 62.5 kg/ha (25% dosage) without biofertilizer application (TC), were extracted for DNA. Those DNA were amplified using primer-GC, hence, analyzed using DGGE. The nifH gene had high variability more than nifD gene. It was expected that there were at least 7 kinds of nifH gene in sample C, 5 in sample TC, and 1 in sample K. High genetic variability of nifH genes was caused evolutionary line. In the other hand, nifD genes tended to be conserved.
Keyword: nitrogen fixation., DGGE, nifD, nifH

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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