Filamentous cyanobacteria and hydrophobic protein in extracellular polymeric substances facilitate algae-bacteria aggregation during partial nitrification

Mei Zhi; Yiying Zhao; Xinyu Zeng; Naga Raju Maddela; Yeyuan Xiao; Yucheng Chen; Ram Prasad; Zhongbo Zhou

doi:10.1016/j.ijbiomac.2023.126379

Filamentous cyanobacteria and hydrophobic protein in extracellular polymeric substances facilitate algae-bacteria aggregation during partial nitrification

Int J Biol Macromol. 2023 Aug 16:251:126379. doi: 10.1016/j.ijbiomac.2023.126379. Online ahead of print.

Authors

Mei Zhi¹, Yiying Zhao², Xinyu Zeng², Naga Raju Maddela³, Yeyuan Xiao⁴, Yucheng Chen¹, Ram Prasad⁵, Zhongbo Zhou⁶

Affiliations

¹ College of Resources and Environment, Southwest University, Chongqing 400715, China; Chongqing Engineering Research Center of Rural Cleaner Production, Chongqing 400715, China.
² College of Resources and Environment, Southwest University, Chongqing 400715, China.
³ Departamento de Ciencias Biológicas, Facultad de Ciencias de la Salud, Universidad Técnica de Manabí, Portoviejo 130105, Ecuador.
⁴ Department of Civil and Environmental Engineering, Shantou University, Shantou 515063, China.
⁵ Department of Botany, Mahatma Gandhi Central University, Motihari, Bihar 845401, India. Electronic address: rpjnu2001@gmail.com.
⁶ College of Resources and Environment, Southwest University, Chongqing 400715, China; Chongqing Engineering Research Center of Rural Cleaner Production, Chongqing 400715, China. Electronic address: zhouzhongbo-1986@163.com.

PMID: 37595699
DOI: 10.1016/j.ijbiomac.2023.126379

Abstract

In algae-bacteria symbiotic wastewater treatment, the excellent settling performance of algae-bacteria aggregates is critical for biomass separation and recovery. Here, the composition of extracellular polymeric substances (EPS), microbial profiles, and functional genes of algae-bacteria aggregates were investigated at different solid retention times (SRTs) (10, 20, and 40 d) during partial nitrification in photo sequencing bioreactors (PSBRs). Results showed that SRTs greatly influenced the nitrogen transformation and the formation and morphological structure of algae-bacteria aggregates. The highest nitrite accumulation, the largest particle size (~1.54 mm) and the best settling performance were observed for the algae-bacteria aggregates in the PSBR with an SRT of 10 d, where the abundant occurrence of filamentous cyanobacteria with the highest ratio of chlorophyll a/b and the lowest EPS amount with the highest protein-to-polysaccharide ratio were observed. In particular, the EPS at 10 d of SRT contained a higher amount of protein-related hydrophobic groups and a lower ratio of α-helix/(β-sheet + random coil), indicating a looser protein structure, which might facilitate the formation and stabilization of algae-bacteria aggregates. Moreover, algal-bacterial aggregation greatly depended on the composition and evolution of filamentous cyanobacteria (unclassified _o__Oscillatoriales and Phormidium accounted for 56.29 % of the identified algae at SRT 10 d). The metagenomic analysis further revealed that functional genes related to amino acid metabolism (e.g., genes of phenylalanine, tyrosine, and tryptophan biosynthesis) were expressed at high levels within 10 d of SRT. Overall, this study demonstrates the influence of EPS structures and filamentous cyanobacteria on algae-bacteria aggregation and reveals the biological mechanisms driving photogranule structure and function.

Keywords: Algae—bacteria aggregates; Extracellular polymeric substances; Filamentous cyanobacteria; Granular sludge; Metagenomic analysis.