Nitrogen removal efficiency of some bacterial strains isolated from seawater in Thua Thien Hue, Vietnam

Background: Nitrifying bacteria in aquaculture environments are capable of removing toxic nitrogen compounds such as ammonium and nitrite. Using these indigenous microbial resources can improve shrimp production.Methods: Screening method was used to isolate aerobic strains of nitrifying bacteria. Species identification for these isolates was done by biomolecular method based on 16S rDNA gene sequence. Ammonium, nitrite and nitrate concentrations from the culture were determined by spectrophotometry at the appropriate wavelength. Temperature, pH, dissolved oxygen and salinity were measured by specialized equipment. Formation and development of flocs during shrimp culture were determined based on their volume and weight. A trial of shrimp nursery was carried out on a small scale with 0.5 m3 tanks containing diluted seawater to 16-18‰ salinity at a density of 400 individual/m3 for 24 days on April 2019. Results: This study isolated two strains of Pseudomonas (BF01 and BF03) and one strain of Cupriavidus oxalaticus BF02 from seawater in Thua Thien Hue province, Vietnam. These bacterial isolates have shown ability to remove nitrogen compounds such as ammonium, nitrite and nitrate in culture medium. Formation and development of flocs were found in trials of shrimp nursery with diluted seawater containing the isolates. Some water quality parameters (temperature, pH, dissolved oxygen, salinity, ammonium and nitrite) were kept at a safe level and juvenile shrimp grown normally during culture.Conclusion: The observations on the water quality and basic growth parameters of juvenile shrimp in the two treatments, diluted seawater and diluted seawater with commercial microbial products, showed that there were no significant differences between them with p = 0.05. This proves that three isolates have played an important role in shrimp nursery.   Keywords: Cupriavidus oxalaticus; Floc; Litopenaeus vanamei; Nitrifying-denitrifying bacteria; Pseudomonas sp.

THỬ NGHIỆM TẠO BIOFLOC TỪ NGUỒN VI SINH TỰ NHIÊN CHO ƯƠNG GIỐNG TÔM THẺ CHÂN TRẮNG TẠI TỈNH THỪA THIÊN HUẾ

This study was conducted to investigate the formation of biofloc in maintaining the stability of the water quality in the white-leg shrimp nursery system. A treatment unit using microorganisms from natural water was conducted to compare with a control supplemented with commercial probiotics. Shrimp were cultured under the conditions of limited sunlight for 24 days without water exchange and with daily molasses addition as a carbon source (the C/N ratio is 15:1). The resulting biofloc complex could control the increase of NH4+ and NO2– via heterotrophic assimilation and nitrification. During the experiments, the N–NH4 and N–NO2 concentrations of the biofloc system maintain a safe range for the juveniles at 0.99 ± 0,02 and 0.49 ± 0.08 mg·L–1, respectively. At the culture density of 400 shrimp/m3, the shrimp weight increases from 0.01 g to 0.59 g per shrimp on the 24th day of culture for all culture tanks with a survival rate of 82.5%.Nghiên cứu này được thực hiện nhằm tìm hiểu khả năng hình thành biofloc để duy trì sự ổn định của môi trường nước trong hệ thống ương giống tôm thẻ chân trắng. Một tổ hợp vi sinh phát triển từ nguồn nước tự nhiên được sử dụng để so sánh với đối chứng có bổ sung chế phẩm vi sinh công nghiệp. Tôm được nuôi trong điều kiện hạn chế ánh sáng mặt trời trong 24 ngày, không có sự trao đổi nước và có bổ sung rỉ mật hàng ngày để làm nguồn carbon (tỷ lệ C/N ở mức 15:1). Tổ hợp biofloc hình thành đã kiểm soát lượng NH4+ và NO2– bằng quá trình đồng hóa dị dưỡng và nitrate hóa. Trong suốt quá trình thí nghiệm, hàm lượng N–NH4 và N–NO2 của hệ thống biofloc được duy trì ở mức an toàn đối với tôm con, lần lượt là 0,99 ± 0,02 mg·L–1 và 0,49 ± 0,08 mg·L–1. Ở mật độ nuôi 400 con·m–3, khối lượng tôm tăng từ 0,01 đến 0,59 g·con–1 sau 24 ngày nuôi ở tất cả các bể với tỷ lệ sống đạt 82,5%

Aetiologies of central nervous system infection in Viet Nam: a prospective provincial hospital-based descriptive surveillance study.

Infectious diseases of the central nervous system (CNS) remain common and life-threatening, especially in developing countries. Knowledge of the aetiological agents responsible for these infections is essential to guide empiric therapy and develop a rational public health policy. To date most data has come from patients admitted to tertiary referral hospitals in Asia and there is limited aetiological data at the provincial hospital level where most patients are seen.We conducted a prospective Provincial Hospital-based descriptive surveillance study in adults and children at thirteen hospitals in central and southern Viet Nam between August 2007-April 2010. The pathogens of CNS infection were confirmed in CSF and blood samples by using classical microbiology, molecular diagnostics and serology.We recruited 1241 patients with clinically suspected infection of the CNS. An aetiological agent was identified in 640/1241 (52%) of the patients. The most common pathogens were Streptococcus suis serotype 2 in patients older than 14 years of age (147/617, 24%) and Japanese encephalitis virus in patients less than 14 years old (142/624, 23%). Mycobacterium tuberculosis was confirmed in 34/617 (6%) adult patients and 11/624 (2%) paediatric patients. The acute case fatality rate (CFR) during hospital admission was 73/617 (12%) in adults and to 42/624 (7%) in children.Zoonotic bacterial and viral pathogens are the most common causes of CNS infection in adults and children in Viet Nam