Judul: Isolation and Selection of Bacillus sp. as the Microbial Agent for Ammonia, Nitrite and Nitrate Degradation in Catfish dan Goldfish Rearing Environment.
Abstrak: Intensive fish farming which applying high stocking densities requires a high amount of feed input. This will result in accumulation of organic and inorganic materials (including ammonia, nitrite and nitrate compounds) which are toxic to fish. Those problems can be resolve by the application of probiotics which have the ability for bioremediation as Bacillus sp. The spores of Bacillus sp. have advantages because it is more stable for a long time. The use of probiotic Bacillus sp. involved in nitrification and denitrification processes in aerobic condition will reduce the accumulation of ammonia, nitrite and nitrate in the fish rearing environment, since the compounds will be converted into nitrogen gas. This study aimed to isolate and select Bacillus sp. species as a potential microbial agent which will degradate the toxic metabolites such as ammonia, nitrite and nitrate These research have four stages : (1) the isolation of Bacillus sp. from water, waterplant’s root and sediment in freshwater fish ponds,(2) the selection of bacteria in basal media for nitrification and denitrification,(3) the selection of bacteria in synthetic pond water medium and (4) the selection of Bacillus sp. ability in the in vivo test (. in catfish and goldfish rearing environment). Among collection of our isolates, Bacillus cereus and Bacillus subtilis showed the highest ammonia degradation; as much as 56,60% and 63,18% respectively from the initial concentration of 131 mg/l TAN (Total Ammonia Nitrogen); and nitrate compound as much as 40,97% and 26,51% respectively from the initial concentration 530 mg/l. The mixed of two isolates designated by Bacillus cereus and Bacillus subtilis in synthetic pond water showed the highest capability in oxidizing ammonia (66,32%) from the initial concentration of 30,2 mg/l TAN and the reduction of nitrite (19,77%) from the initial concentration of 0,263 mg/l nitrite and nitrate (28,37%) compounds from the initial concentration of 32,6 mg/l nitrate. In the in vivo experiment, using carp and catfish (4-5 cm) in the aquaria (30 l). Each fish exposed in the control water (without inoculation of bacteria) and treatment water (with a mixture of Bacillus cereus and Bacillus subtilis inoculation, 109 cfu/ml total isolate, 3 ml/aquaria). In the in vivo experiments, TAN and nitrate concentrations in treatments inoculated by isolates were lower compared to that of control (without any isolate inoculation) (statistical tests P <0.05), whereas the nitrite concentration in the control and treatment were not significantly different. The inoculation of Bacillus cereus and Bacillus subtilis Keywords: Bacillus sp., ammonia degradation, degradation of nitrite, nitrate reduction showed ammonia degradation as much as 30% from the initial concentration of 6,12 mg/l TAN, and reduce carp and catfish’s mortality compared to that of control.
Keyword: Bacillus sp, ammonia degradation, degradation of nitrite, nitrate reduction

Judul: Isolasi dan Seleksi Bacillus sp. dari Media Pemeliharaan Air Tawar Sebagai Pendegradasi Amonia, Nitrit, dan Nitrat.
Abstrak: Peningkatan produksi budidaya ikan air tawar secara intensif dapat menyebabkan penurunan kualitas air yang disebabkan oleh faktor kelebihan pemberian pakan (overfeeding) dan hasil metabolisme hewan pemeliharaan. Pemberian probiotik sebagai agen bioremediasi merupakan tindakan antisipatif yang dapat dilakukan untuk mempertahankan kualitas pada media budidaya tersebut. Bacillus sp. merupakan bakteri heterotrof yang mampu melakukan proses bioremediasi sehingga dapat menggunakan amonia, nitrit dan nitrat sebagai substratnya serta mengubahnya menjadi gas nitrogen. Dari hasil isolasi terdapat empat isolat (W1,W2,S1,S2) yang terseleksi dan berpotensi sebagai agen pendegradasi senyawa metabolit toksik amonia, nitrit dan nitrat. Seleksi dalam media nitrifikasi dan denitrifikasi secara in vitro juga memberikan hasil bahwa semua isolat mampu mengoksidasi TAN berkisar antara 11.62-47.91% dan mereduksi nitrat sebanyak 4.89-28.86%. S2, yang teridentifikasi sebagai Bacillus cereus merupakan kandidat probiotik yang memiliki kemampuan terbaik serta tidak termasuk dalam jenis bakteri yang virulen dalam uji patogenisitas. Bacillus cereus juga mampu mengoksidasi TAN sebanyak 10.84 mg L-1 (47.91%) dan mereduksi nitrat sebanyak 15.10 mg L-1 (28.86%).
Keyword: amonia, Bacillus sp., nitrat, nitrit

Judul: : Persamaan Tunggal sebagai Representasi Kurva Komposit
Abstrak: A mathematical method is introduced to represent a composite curve based on an extension of analytic geometry. The representation is given either with a single equation or with two equations, in the case of parametric representation. This method permits the representation of composite curves in similar manner to the conventional representation of non-composite curves. Some mathematical tools, including Heaviside unit step function and periodizer function, are used in the establishment of a single equation. In this paper, regular equations of regular and irregular polygon, as well as composite curves of two dimensions, are implemented using a computer algebraic system, Mathematica.
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