Iron-dependent mutualism between Chlorella sorokiniana and Ralstonia pickettii forms the basis for a sustainable bioremediation system

Abstract

Phototrophic communities of autotrophic microalgae and heterotrophic bacteria perform complex tasks of nutrient acquisition and tackling environmental stress but remain underexplored as a basis for the bioremediation of emerging pollutants. In industrial monoculture designs, poor iron uptake by microalgae limits their productivity and biotechnological efficacy. Iron supplementation is expensive and ineffective because iron remains insoluble in an aqueous medium and is biologically unavailable. However, microalgae develop complex interkingdom associations with siderophore-producing bacteria that help solubilize iron and increase its bioavailability. Using dye degradation as a model, we combined environmental isolations and synthetic ecology as a workflow to design a simplified microbial community based on iron and carbon exchange. We established a mutualism between the previously non-associated alga Chlorella sorokiniana and siderophore-producing bacterium Ralstonia pickettii . Siderophore-mediated increase in iron bioavailability alleviated Fe stress for algae and increased the reductive iron uptake mechanism and bioremediation potential. In exchange, C. sorokiniana produced galactose, glucose, and mannose as major extracellular monosaccharides, supporting bacterial growth. We propose that extracellular iron reduction by ferrireductase is crucial for azoreductase-mediated dye degradation in microalgae. These results demonstrate that iron bioavailability, often overlooked in cultivation, governs microalgal growth, enzymatic processes, and bioremediation potential. Our results suggest that phototrophic communities with an active association for iron and carbon exchange have the potential to overcome challenges associated with micronutrient availability, while scaling up bioremediation designs.

Elucidating Multiple Electron-Transfer Pathways for Metavanadate Bioreduction by Actinomycetic Streptomyces microflavus

“…This decrease was attributable to the consumption of organic carbon, which served as an essential energy source and electron donor for S. microflavus in the removal of heavy metals . A mass balance evaluation revealed that more organic matter was consumed than required for V­(V) reduction, as the growth metabolism and biomass synthesis of S.…”

“…This decrease was attributable to the consumption of organic carbon, which served as an essential energy source and electron donor for S. microflavus in the removal of heavy metals. 53 A mass balance evaluation revealed that more organic matter was consumed than required for V(V) reduction, as the growth metabolism and biomass synthesis of S. microflavus necessitated an ample supply of carbon sources. 18 Over the course of V(V) reduction, biomass steadily increased, signifying the respiration of V(V) by S. microflavus via electron transfer.…”

Enhanced phycocyanin production of Arthrospira maxima by addition of mineral elements and polypeptides using response surface methodology

“…The addition of Se increased the phycocyanin concentration of Arthrospira maxima from 226 to 274 mg L -1 which was 21.2% higher than that in the control group (Chen et al, 2006). Most studies on the influence of mineral elements on phycocyanin presently focused on a single factor, such as Ni, Ca and Fe (Sloth et al, 2006;Velu et al, 2019;Rawat et al, 2022;Yang et al, 2022), and showed a good effect on phycocyanin. Arthrospira requires a small number of mineral components to grow.…”

Exchange or Eliminate: The Secrets of Algal-Bacterial Relationships

“…Siderophore-mediated iron chelation enhances the formation of bioavailable iron complexes, which algae can then absorb through plasma membrane-bound ferrireductase [ 128 ]. Consequently, the introduction of siderophore-producing Ralstonia pickettii establishes a mutualistic relationship whereby the bacteria benefit from the photosynthetically fixed algal exopolysaccharides while reciprocally enhancing the growth and degradation of complex azo dyes by C. sorokiniana [ 129 ].…”