Permeable (sandy) marine sediments are dynamic environments, with oxic-anoxic boundaries constantly changing due to wave oscillations and tidal cycles [1]. As such, this environment selects for metabolically flexible bacteria such as facultative anaerobes; capable of utilizing different electron acceptors and donors based on availability [2]. We measured the dominant carbon degradation pathways taking place within these sands by incubation with 13C labelled glucose (1-13C; 2-13C; 3-13C; 13C6) and subsequent measurements of 13CO2. Results showed that anoxic sands across a variety of high energy sandy sites mediate fermentation via the Embden-Meyerhof fermentation pathway, remaining uncoupled from terminal respiration processes [2-3]. The build-up of acetate, a major product of fermentation, is then expected, however to date we have observed no significant accumulation in anoxic sediments [3] and the question remains as to the fate of the metabolic end products? It is speculated that these facultative anaerobes are storing organic carbon intracellularly in the form of lipids or PHAs [2-4]. Here we present ex situ incubations of dynamic sands and pure culture experiments of facultative anaerobes and in combination with metabolomics we further explore the possibility that bacteria are storing energy intracellularly via molecules such as glycogen, polyhydroxyalkanoates (PHAs), triacylglycerols (TAGs) and wax esters (WEs).
[1] Precht et al. (2004) Limnol. Oceanogr. 57, 1217-1232.
[2] Kessler et al. (2019) Nat. Microbiol. 4, 1014-1023.
[3] Bourke et al. (2017) Nat. Geosci. 10, 30-35.
[4] Kessler et al. (2020) Geochim. Cosmochim. Acta 279, 16-28.