Chameleon-like Anammox Bacteria for Surface Color Change after Suffering Starvation

Abstract

Bacteria are often exposed to long-term starvation during transportation and storage, during which a series of enzymes and metabolic pathways are activated to ensure survival. However, why the surface color of the bacteria changes during starvation is still not well-known. In this study, we found black anammox consortia suffering from long-term starvation contained 0.86 mmol gVSS −1 cytochrome c, which had no significant discrepancy compared with the red anammox consortia (P > 0.05), indicating cytochrome c was not the key issue for chromaticity change. Conversely, we found that under starvation conditions cysteine degradation is an important metabolic pathway for the blackening of the anammox consortia for H 2 S production. In particular, anammox bacteria contain large amounts of iron-rich nanoparticles, cytochrome c, and other iron−sulfur clusters that are converted to produce free iron. H 2 S combines with free iron in bacteria to form Fe−S compounds, which eventually exist stably as FeS 2 , mainly in the extracellular space. Interestingly, FeS 2 could be oxidized by air aeration, which makes the consortia turn red again. The unique self-protection mechanism makes the whole consortia appear black, avoiding inhibition by high concentrations of H 2 S and achieving Fe storage. This study expands the understanding of the metabolites of anammox bacteria as well as the bacterial survival mechanism during starvation.

Insight into the Regulation Mechanism of Iron Oxide Nanoparticles in Anammox Consortia: Autophagy-Dependent Ferroptosis

“…The heme c content in R 1 was 1.24 μmol g of VSS –1 in Phase 0 and increased to 1.6 μmol g of VSS –1 in Phase 2 followed by a decrease to 1.1 μmol g of VSS –1 in Phase 3 (Figure ). These changes manifested that the effect of γ-Fe 2 O 3 NPs on heme c was concentration-dependent, which could be explained by low-concentration promotion and high-concentration inhibition. , The Pearson correlation analysis showed a positive correlation between heme c and SAA, and their significant negative correlations ( p < 0.05) with Fe­(II) and Fe­(III) (Figure S9). The synthesis of heme c requires energy.…”