Yucheng Wu Xiubin Ke Marcela Hernández Baozhan Wang Marc G. Dumont Zhongjun Jia and Ralf Conrad.Autotrophic growth of bacterial and archaeal ammonia oxidizers in freshwater sediment microcosms incubated at different temperatures. Applied and Environmental Microbiology 2013 doi: 10.1128-​AEM.00061-13

Abstract

Both bacteria and archaea potentially contribute to ammonia oxidation but their roles in freshwater sediment are still poorly understood. Seasonal differences in the relative activity of these groups might exist since cultivated archaeal ammonia oxidizers have higher temperature optima than their bacterial counterparts. In this study sediment collected from the eutrophic freshwater Lake Taihu (China) was incubated at different temperatures (4°C 15°C 25°C and 37°C) for up to 8 weeks. We examined the active bacterial and archaeal ammonia oxidizers in these sediment microcosms by combined stable isotope probing (SIP) and molecular community analysis. The results showed that accumulation of nitrate in microcosms correlated negatively with temperature although ammonium depletion was the same which might be related to an enhanced activity of other nitrogen transformation processes. Incubation at different temperatures significantly changed the microbial community composition as revealed by 454 pyrosequencing targeting bacterial 16S rRNA genes. After 8-weeks incubation ¹³C-bicarbonate labeling of bacterial amoA genes which encode the ammonia monooxygenase subunit A and an observed increase in copy numbers indicated the activity of ammonia-oxidizing bacteria in all microcosms. Nitrosomonas sp. Is79A3 and Nitrosomonas communis lineages dominated the heavy fraction of CsCl gradients at low and high temperatures respectively indicating a niche differentiation of active bacterial ammonia oxidizers along the temperature gradient. The ¹³C-labelling of ammonia-oxidizing archaea in microcosms incubated at 4-25°C was minor. In contrast significant ¹³C-labell