Cross-Feeding between Filamentous Cyanobacteria and Symbiotic Bacteria Favors Rapid Photogranulation

Abstract

Photogranules are dense algal-bacterial aggregates used in aeration-free and carbon-negative wastewater treatment, wherein filamentous cyanobacteria (FC) are essential components. However, little is known about the functional role of symbiotic bacteria in photogranulation. Herein, we combined cyanobacterial isolation, reactor operation, and multiomics analysis to investigate the cyanobacterialbacterial interaction during photogranulation. The addition of FC to the inoculated sludge achieved a 1.4-fold higher granule size than the control, and the aggregation capacity of FC-dominant photogranules was closely related to the extracellular polysaccharide (PS) concentration (R = 0.86). Importantly, we found that cross-feeding between FC and symbiotic bacteria for macromolecular PS synthesis is at the heart of photogranulation and substantially enhanced the granular stability. Chloroflexiaffiliated bacteria intertwined with FC throughout the photogranules and promoted PS biosynthesis using the partial nucleotide sugars produced by FC. Proteobacteria-affiliated bacteria were spatially close to FC, and highly expressed genes for vitamin B1 and B12 synthesis, contributing the necessary cofactors to promote FC proliferation. In addition, Bacteroidetes-affiliated bacteria degraded FC-derived carbohydrates and influenced granules development. Our metabolic characterization identified the functional role of symbiotic bacteria of FC during photogranulation and shed light on the critical cyanobacterial-bacterial interactions in photogranules from the viewpoint of cross-feeding.

Zero-Valent Iron Enhances Nutrient Removal and Long-Term Stability of Algal–Bacterial Granular Sludge under Low Carbon Conditions

“…Till the 110th day, compared with the yellowish granules in R1, mature granules formed in R2 and R3 exhibited green or dark green spherical structures, and the total chlorophyll a concentration stabilized at values of 2.73 and 2.04 mg/g MLVSS, respectively (Figure S2a), indicating a well-maintained symbiotic balance between algae and bacteria in R2 and R3 . In addition, the chlorophyll a /chlorophyll b ratio in R2 was higher than that in R3 (Figure S2a), indicating growing predominance of Cyanobacteria in R2 . CLSM images further reveal the pronounced fluorescence intensity of eukaryotic microalgae and the comparatively lower fluorescence intensity of Cyanobacteria in R3, suggesting that ZVI facilitated the preferential enrichment of eukaryotic microalgae rather than Cyanobacteria (Figure S2b).…”

Organics removal pathways and algae-bacteria interactions of microalgal-bacterial granular sludge treating real municipal wastewater

“…As an energy-saving and environmentally-sustainable process, the microalgalbacterial granular sludge (MBGS) can directly utilize solar energy to generate oxygen 7,8 , which is further used assimilate wastewater organics and nutrients into microalgae biomass, while helping to mitigate carbon emissions 9 . In fact, the MBGS process can even absorb carbon dioxide of industrial origin 10 and methane 11 , which is more conducive to achieving the carbon neutrality of wastewater treatment 12,13,14 .…”