NanoSIMS reveals unusual enrichment of acetate and propionate by an anammox consortium dominated by Jettenia asiatica.

Anaerobic ammonium-oxidizing (anammox) bacteria convert ammonium and nitrite into N 2 in a chemolithoautotrophic way, meaning that they utilize CO 2 /HCO 3 solely as their carbon sources. Such autotrophic behavior limits their competitiveness with heterotrophic microorganisms in both natural environments and engineered systems. Recently, environmental metagenomic results have indicated the capability of anammox bacteria to metabolize short-chain fatty acids, further confirmed by limited experimental evidence based on highly enriched cultures. However, clear evidence is difficult to get because of the limits of traditional methodologies which rely on the availability of a pure anammox culture. In this study, we identified and quantified the uptake of acetate and propionate, on a single-cell level, by an anammox consortium that was dominated by Candidatus Jettenia asiatica (relative abundance of 96%). The consortium, growing in granular form with an average relative abundance of anammox bacteria of 96.0%, was firstly incubated in a13C-labelled acetate or propionate medium; then microtome sections were scanned by a nanometer-scale secondary ion mass spectrometer (NanoSIMS). The NanoSIMS scannings revealed that the consortium enriched acetate and propionate at a >10 times higher efficiency than bicarbonate incorporation. Our results also suggest that acetate or propionate was likely not assimilated by J. asiatica directly, but firstly oxidized to CO 2 , which then served as carbon sources for the follow-up autotrophy in J. asiatica cells. Furthermore, more [15N]ammonium was enriched by the propionate-fed consortium than the acetate-fed consortium despite that exactly the same amount of 13C atoms were supplied. Our study strongly indicates an alternative lifestyle, namely organotrophy, in addition to chemolithoautotrophy of anammox bacteria, making it more versatile than often expected. It suggests that the niche of anammox bacteria in both natural and engineered ecosystems can be much broader than usual assumed. Recognising this is important for their role in wastewater treatment and the global nitrogen turn-over rates. Image 1 • NanoSIMS reveals acetate- and propionate-engaged anammox processes. • The uptake of acetate and propionate by Jettenia asiatica was identified. • An alternative lifestyle to chemolithoautotrophy of anammox bacteria was proposed. [ABSTRACT FROM AUTHOR]