RESUMEN
Nitrous oxide (N2O) is atmospheric trace gas that contributes to climate change and affects stratospheric and ground-level ozone concentrations. Ammonia oxidizers and denitrifiers contribute to N2O emissions in estuarine waters. However, as an important climate factor, how temperature regulates microbial N2O production in estuarine water remains unclear. Here, we have employed stable isotope labeling techniques to demonstrate that the N2O production in estuarine waters exhibited differential thermal response patterns between nearshore and offshore regions. The optimal temperatures (Topt) for N2O production rates (N2OR) were higher at nearshore than offshore sites. 15N-labeled nitrite (15NO2-) experiments revealed that at the nearshore sites dominated by ammonia-oxidizing bacteria (AOB), the thermal tolerance of 15N-N2OR increases with increasing salinity, suggesting that N2O production by AOB-driven nitrifier denitrification may be co-regulated by temperature and salinity. Metatranscriptomic and metagenomic analyses of enriched water samples revealed that the denitrification pathway of AOB is the primary source of N2O, while clade II N2O-reducers dominated N2O consumption. Temperature regulated the expression patterns of nitrite reductase (nirK) and nitrous oxide reductase (nosZ) genes from different sources, thereby influencing N2O emissions in the system. Our findings contribute to understanding the sources of N2O in estuarine waters and their response to global warming.
RESUMEN
Ammonia oxidation, performed by ammonia-oxidizing archaea (AOA) and bacteria (AOB), plays a critical role in the cycle of nitrogen in the ocean. For now, environmental variables controlling distribution of ammonia-oxidizing microbes are still largely unknown in oceanic environments. In this study, we used real-time quantitative PCR and high-throughput sequencing methods to investigate the abundance and diversity of AOA and AOB from sediment and water in Zhanjiang Bay. Phylogenic analysis revealed that the majority of AOA amoA sequences in water and sediment were affiliated with the genus Nitrosopumilus, whereas the Nitrosotalea cluster was only detected with low abundance in water. Nitrosomonas and Nitrosospira dominated AOB amoA sequences in water and sediment, respectively. The amoA copy numbers of both AOA and AOB varied significantly with month for both sediment and water. When water and sediment temperature dropped to 17-20°C in December and February, respectively, the copy number of AOB amoA genes increased markedly and was much higher than for AOA amoA genes. Also, AOA abundance in water peaked in December when water temperature was lowest (17-20°C). Stepwise multiple regression analyses revealed that temperature was the most key factor driving monthly changes of AOA or AOB abundance. It is inferred that low water temperature may inhibit growth of phytoplankton and other microbes and so reduce competition for a common substrate, ammonium.
Asunto(s)
Amoníaco/metabolismo , Bacterias/aislamiento & purificación , Bahías/microbiología , Bacterias/clasificación , Bacterias/genética , Bacterias/metabolismo , Proteínas Bacterianas/genética , Proteínas Bacterianas/metabolismo , Biota , Sedimentos Geológicos/microbiología , Oxidación-Reducción , Filogenia , Estaciones del Año , Agua de Mar/microbiologíaRESUMEN
Nitrospira is the most diverse genus of nitrite-oxidizing bacteria, and its members are widely spread in various natural and engineered ecosystems. In this study, the phylogenetic diversity of Nitrospira and monthly changes of its abundance from Zhanjiang Bay were investigated. Phylogenetic analysis showed that among 58 OTUs with high abundance, 74% were not affiliated with any previously described Nitrospira species, revealing a previously unrecognized diversity of coastal Nitrospira. The abundances of both Nitrospira and Nitrospina exhibited a significantly monthly change. During most of the months, abundance of Nitrospina was greater than that of Nitrospira. In particle-attached communities, either abundance of Nitrospina or Nitrospira was highly correlated with that of ammonia-oxidizing archaea (AOA), whereas abundance of ammonia-oxidizing bacteria was only highly correlated with that of Nitrospina. In free-living communities, either abundance of Nitrospina or Nitrospira was correlated only with that of AOA. These results suggest that both Nitrospira and Nitrospina can be involved in nitrite oxidation by coupling with AOA, but Nitrospina may play a greater role than Nitrospira in this tropical bay.