Microbiota succession, species interactions, and metabolic functions during autotrophic biofloc formation in zero-water-exchange shrimp farming without organic carbon supplements.

Autotrophic bioflocs (ABF) exhibits lower energy consumption, more environment-friendly and cost-effective than heterotrophic bioflocs depending on organic carbon supplements. Whereas ABF has not been widely applied to aquaculture production. Here, ABF successfully performed to control ammonia and nitrite under harmless levels even when carbon-to-nitrogen ratio reduced to 2.0, during 12-week shrimp farming in commercial scale. ABF was mainly dominated by bacteria of Proteobacteria, Bacteroidota, Chloroflexi and eukaryotes of Bacillariophyta, Rotifera, Ciliophora. A notable shift occurred in ABF with the significant decreases of Proteobacteria and Rotifera replaced by Bacteroidota, Chloroflexi, and Bacillariophyta after four weeks. Nitrogen metabolism was synergistically executed by bacteria and microalgae, especially the positive interaction between Nitrospira and Halamphora for ABF nitrification establishment. Metagenomics confirmed the complete functional genes of key bacteria related to the cycling of carbon, nitrogen, and phosphorus by ABF. This study may promote the development application of ABF in low-carbon shrimp aquaculture.

Effects of light intensity and salinity on formation and performance of microalgal-bacterial granular sludge.

Photosynthetic microorganisms in microalgal-bacterial granular sludge offer advantages in wastewater treatment processes. This study examined the effects of light intensity and salinity on microalgal-bacterial granular sludge formation and microbial changes. Activated sludge was inoculated into three bioreactors and operated in batch treatment mode for 100 days under different light intensities (0, 60, and 120 µmol m-2 s-1) and staged increases in salinity concentration (0, 1, 2, and 3%). Results showed that microalgal-bacterial granular sludge was successfully formed within 30 days, and high light exposure increased algal particle stability and inorganic nitrogen removal (63, 66, 71%), while chemical oxygen demand removal (>95%) was similar across groups. High-throughput sequencing results showed that the critical algae were Chlorella and diatoms, while the main bacteria included Paracoccus and Xanthomarina with high extracellular polymeric substance production. This study aims to enhance the comprehension of MBGS processes in saline wastewater treatment under varying light intensities.

Toxicological Effects of Microplastics and Sulfadiazine on the Microalgae Chlamydomonas reinhardtii.

Despite the fact that microplastics (MPs) facilitate the adsorption of environmental organic pollutants and influence their toxicity for organisms, more study is needed on the combination of MPs and antibiotics pollutant effects. In this study, polystyrene MPs (1 and 5 µm) and sulfadiazine (SDZ) were examined separately and in combination on freshwater microalga, Chlamydomonas reinhardtii. The results suggest that both the MPs and SDZ alone and in combination inhibited the growth of microalgae with an increasing concentration of MPs and SDZ (5-200 mg l-1); however, the inhibition rate was reduced by combination. Upon exposure for 7 days, both the MPs and SDZ inhibited algal growth, reduced chlorophyll content, and enhanced superoxide dismutase (SOD) activities, whereas glutathione peroxidase (GSH-Px) activity was elevated only with the exposure of 1 µm MPs. Fluorescence microscopy and scanning electron microscopy also indicated that particle size contributed to the combined toxicity by aggregating MPs with periphery pollutants. Further, the amount of extracellular secretory protein increased in the presence of MPs and SDZ removal ratio decreased when MPs and SDZ coexisted, suggesting that MPs affected SDZ metabolism by microalgae. The particle size of microplastics affected the toxicity of MPs on microalgae and the combined effect of MPs and SDZ could be mitigated by MPs adsorption. These findings provide insight into microalgae responses to the combination of MPs and antibiotics in water ecosystems.