| Popis: |
Traditionally, ammonia oxidation has been associated with ammonia oxidising bacteria (AOB) and molecular approaches have demonstrated significant AOB diversity and links between AOB community structure and function (nitrification rate). Recent research indicates that ammonia oxidising archaea (AOA) may also contribute to global nitrification, following evidence of wide environmental distribution of archaeal amoA genes (encoding ammonia monooxygenase). Two recently developed, culture-independent molecular techniques for assessment of microbial activity were optimised and used to study activity of AOB communities. The first, stable isotope probing (SIP) relies on incorporation of specific 13C-labelled substrates into nucleic acids of actively growing microorganisms. The second involves analysis of expression of the functional gene amoA. Both techniques revealed differences in activity patterns under incubation at different ammonia concentrations. However, SIP proved difficult to apply to soil systems and transcriptional activity of the amoA gene was subsequently used to investigate the effect of temperature (10-30°C) on activity of AOB and AOA. AOB appeared dormant in soil microcosms but AOA activity was indicated by increased in nitrification, with temperature, associated with increases in both 16S rRNA and amoA gene and gene transcript abundance. In addition, changes in the AOA community structure were observed with increases or decreases in relative abundance of specific phylotypes with increasing temperature and nitrification. In conclusion, the study provided evidence that, in the soil system studied here, AOA were the major ammonia oxidisers but that temperature had little effect on community structure. |
