We measured benthic denitrification (DN) and dissimilatory reduction of nitrate to ammonium (DNRA) using the isotope-pairing technique in three tropical estuaries in Thailand (Mae Klong), Indonesia (Cisadane), and Fiji (Vunidawa-Rewa) during rainy, dry, and intermediate seasons along the salinity gradient of each estuary. DNRA dominated. Anammox (AN) was measured initially but neither AN activity nor AN bacteria-related 16S ribosomal RNA genes were detected in any of the estuaries. DN was either zero or extremely low, driven by water column nitrate and not from benthic nitrification-DN. N 2 O was not formed during DN. N 2 O saturations in estuary water were low, except in the nutrified Indonesian estuary, and tropical estuaries are therefore likely to be only small sources of N 2 O. Benthic nitrate reduction was nitrate limited; when nitrate was enhanced experimentally, DN increased slightly, but DNRA increased proportionately much more. Predominance of DNRA over DN in tropical estuaries may be due both to an energetic advantage (greater standard free energy change, DGu) of nitrate ammonifiers over denitrifiers when competing for limited nitrate, and also to higher affinity for nitrate by the nitrate ammonifiers. At tropical temperatures the three processes occur in the order DNRA . DN . AN. In contrast, temperate estuaries, at lower temperature and higher nitrate concentrations, exhibit proportionately greater levels of AN and DN. The Cisadane estuary became anoxic during the dry season, with high ammonium and sulfide, but no nitrate reduction because of lack of nitrate. Addition of nitrate stimulated high rates of autotrophic DN driven by sulfide, but not DNRA.

Nitrate and nitrite concentrations in the water and nitrous oxide and nitrite fluxes across the sediment-water interface were measured monthly in the River Colne estuary, England, from December 1996 to March 1998. Water column concentrations of N 2 O in the Colne were supersaturated with respect to air, indicating that the estuary was a source of N 2 O for the atmosphere. At the freshwater end of the estuary, nitrous oxide effluxes from the sediment were closely correlated with the nitrite concentrations in the overlying water and with the nitrite influx into the sediment. Increases in N 2 O production from sediments were about 10 times greater with the addition of nitrite than with the addition of nitrate. Rates of denitrification were stimulated to a larger extent by enhanced nitrite than by nitrate concentrations. At 550 M nitrite or nitrate (the highest concentration used), the rates of denitrification were 600 mol N · m ؊2 · h ؊1 with nitrite but only 180 mol N · m ؊2· h ؊1 with nitrate. The ratios of rates of nitrous oxide production and denitrification (N 2 O/N 2 ؋ 100) were significantly higher with the addition of nitrite (7 to 13% of denitrification) than with nitrate (2 to 4% of denitrification). The results suggested that in addition to anaerobic bacteria, which possess the complete denitrification pathway for N 2 formation in the estuarine sediments, there may be two other groups of bacteria: nitrite denitrifiers, which reduce nitrite to N 2 via N 2 O, and obligate nitrite-denitrifying bacteria, which reduce nitrite to N 2 O as the end product. Consideration of free-energy changes during N 2 O formation led to the conclusion that N 2 O formation using nitrite as the electron acceptor is favored in the Colne estuary and may be a critical factor regulating the formation of N 2 O in high-nutrient-load estuaries.Nitrous oxide (N 2 O) is, after molecular nitrogen, the most abundant nitrogen compound in the atmosphere. Global longterm measurement series of tropospheric N 2 O show an annual growth rate of about 0.25 to 0.31% year Ϫ1 (18, 48), indicating that current global sources exceed sinks (4). Nitrous oxide has an atmospheric lifetime of about 150 years and a large greenhouse warming potential (36). When century-long effects are considered, the greenhouse warming potential of N 2 O is 310 times greater than that of CO 2 (1).According to Mathews (26), known global sinks exceed known sources by 40%, which implies either the presence of unknown sources of N 2 O or the underestimation of alreadyknown sources. Generally, global budgets do not include estimates of sources of N 2 O in estuaries and coastal seas. A recent study (2), however, showed that when estuarine and coastal regions were included, a considerable portion (approximately 60%) of the global marine N 2 O flux was from estuarine and coastal regions, mainly due to high emission from estuaries. High N 2 O concentrations and high fluxes to the atmosphere have been described in some estuaries and coastal seas (2,3,6,14,19,24,27,28,35,39,40,41,42,4...

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Calliandra calothyrsus preserved in silage is an alternative method for improving the crude protein content of feeds for sustainable ruminant production. The aim of this research was to evaluate the quality of silage which contained different levels of C. calothyrsus by examining the fermentation characteristics and microbial diversity. Silage was made in a completely randomized design consisting of five treatments with three replications i.e.: R0, Pennisetum purpureum 100%; R1, P. purpureum 75%+C. calothyrsus 25%;, R2, P. purpureum 50%+C. calothyrsus 50%; R3, P. purpureum 25%+C. calothyrsus 75%; and R4, C. calothyrsus 100%. All silages were prepared using plastic jar silos (600 g) and incubated at room temperature for 30 days. Silages were analyzed for fermentation characteristics and microbial diversity. Increased levels of C. calothyrsus in silage had a significant effect (p<0.01) on the fermentation characteristics. The microbial diversity index decreased and activity was inhibited with increasing levels of C. calothyrsus. The microbial community indicated that there was a population of Lactobacillus plantarum, L. casei, L. brevis, Lactococcus lactis, Chryseobacterium sp., and uncultured bacteria. The result confirmed that silage with a combination of grass and C. calothyrsus had good fermentation characteristics and microbial communities were dominated by L. plantarum.

Aims: Tempeh is a soy-based traditional food fermented by Rhizopus oligosporus. Although this mold is the main microorganism responsible for tempeh fermentation, various unknown bacteria presence in tempeh could enhance tempeh's nutritional value. This study is aimed to examine the identity of bacteria in tempeh bacterial community by combining metagenomics analysis and culturable technique. Methodology and results: Samples were obtained from a tempeh producer which consists of raw soybeans, fresh water used to soak the beans, soaking water after the beans were soaked for 18 h, dehulled-soybean before inoculation, starter culture, and fresh tempeh. All samples were plated onto Enterobacteriaceae and Lactic Acid Bacteria agar media, and the total DNA was extracted for metagenomics analysis based on 16S rRNA gene cloning and High-Throughput Sequencing (HTS). Metagenomic analysis indicated that Firmicutes and Proteobacteria were the predominant and subdominant bacteria, respectively, while the culturable technique showed Proteobacteria were the predominant bacteria. Firmicutes species detected in tempeh were similar to the ones in the soaking water, which were populated by Lactobacillus. However, another predominant bacteria from tempeh, Enterococcus, was similar to minor population of Enterococcus detected in dehulled-soybean before inoculation. Based on the cloned 16S rRNA genes, we observed L. agilis, L. fermentum, and E. cecorum as the predominant bacteria in tempeh. The starter culture, which was dominated by Clostridium, did not alter bacterial community in tempeh, since its proportion was only 2.7% in tempeh clean reads. Conclusion, significance and impact of study:The dominant bacteria in tempeh was Lactobacillus from Firmicutes. The bacterial community in tempeh was not affected by the starter culture used, but mainly because of the soybean soaking process.