Extracellular polymeric substances in aerobic granular sludge under increasing salinity conditions

Area of Science:

• Environmental microbiology
• Biochemistry
• Microbial ecology

Background:

• Extracellular polymeric substances (EPS) are crucial for microbial community structure and function.
• Seawater salinity is a key environmental factor influencing microbial adaptation and EPS production.
• Understanding EPS changes under salinity stress is vital for wastewater treatment and microbial ecology.

Purpose of the Study:

• To investigate the long-term effects of increasing seawater salinity on microbial EPS composition and structure.
• To elucidate the adaptive mechanisms of microbial communities, particularly "Candidatus Accumulibacter", to salinity stress.
• To analyze changes in EPS components, including glycans and charged groups, under varying salinity conditions.

Main Methods:

• Stepwise increase in salinity (0-4%) with biomass renewal.
• Fourier-transform infrared spectroscopy (FT-IR) for EPS analysis.
• Lectin microarray to assess glycan diversity in EPS glycoproteins.
• Metaproteomic analysis to identify microbial adaptation pathways.
• Microbial community composition analysis using 16S rRNA sequencing.

Main Results:

• Stable granulation and nutrient removal were maintained across salinities.
• Increasing salinity reduced glycan diversity and increased negative charge in EPS glycoproteins.
• Microbial community shifted to a dominance of "Candidatus Accumulibacter" clade I species at higher salinities.
• Metaproteomics revealed "Ca. Accumulibacter" upregulated genes for cell envelope biosynthesis under salinity stress.
• Putative glycoproteins produced by "Ca. Accumulibacter" were downregulated with increasing salinity.

Conclusions:

• "Candidatus Accumulibacter" dynamically adapts its EPS, especially glycoprotein glycans, to increasing seawater salinity.
• EPS modification is a key strategy for microbial adaptation to environmental stress.
• Findings provide insights into microbial resilience and adaptation mechanisms in saline environments.