Enhanced Secretions of Algal Cell-Adhesion Molecules and Metal Ion-Binding Exoproteins Promote Self-Flocculation of Chlorella sp. Cultivated in Municipal Wastewater

Abstract

The mechanism of self-flocculation remains unclear, partially impeding its efficiency enhancement and commercial application of microalgae-based municipal wastewater (MW) bioremediation technology. This study revealed the contributions of exoproteins [PN, proteins in extracellular polymeric substances (EPS)] to the separation of indigenous microalgae from treated MW. Compared to the low light intensity group, the high light intensity (HL) group produced Chlorella sp. with 4.3-fold higher self-flocculation efficiencies (SE). This was attributed to the enriched biological functions and positional rearrangement of increased PN within 2.9-fold higher EPS. Specifically, a total of 75 PN was over-expressed in the HL group among the 129 PN identified through label-free proteomics. The algal cell-adhesion molecules (Algal-CAMs) and metal-ion-binding PN were demonstrated as two dominant contributors promoting cell adhesion and bridging, through function prediction based on the contained domains. The modeled 3D structure showed that Algal-CAMs presented less hydrophilic α-helix abundance and were distributed in the outermost position of the EPS matrix, further facilitating microalgal separation. Moreover, the 10.1% lower hydrophily degree value, negative interfacial free energy (−19.5 mJ/m2), and 6.8-fold lower energy barrier between cells also supported the observed higher SE. This finding is expected to further fill the knowledge gap of the role of PN in microalgal self-flocculation and promote the development of biomass recovery from the microalgae-wastewater system.

Comparison of single strain, natural algal communities and a native algal bloom: Application for wastewater treatment and biomass generation in cassava biogas effluent

“…Moreover, additional microalgae can increase dissolved oxygen in the system and thus promote the aerobic activity of native bacteria to assimilate nutrients together with the microalgae (Fito & Alemu, 2018). Another mechanism might be related to the enrichment of the biological function of native microbial and positional rearrangement substrates to treat wastewater by the release of extracellular polymeric substance by the algal metabolism activity (Chen et al, 2021). Nevertheless, native bacteria as a contaminant and algal removal in wastewater was reported to change based on the composition of the native bacterial communities in the wastewater (Hassan et al, 2019).…”

Instant Inhibition and Subsequent Self-Adaptation of Chlorella sp. Toward Free Ammonia Shock in Wastewater: Physiological and Genetic Responses

“…For the FA shock experiment, a self-designed photobioreactor (PBR) with a 350 mL working volume was used for microalgal growth in synthetic MW. 20 Two experimental groups were prepared in triplicate: the FA group and the control. For both groups, the exact same operations were initially adopted until Chlorella sp.…”

Unravelling multiple removal pathways of oseltamivir in wastewater by microalgae through experimentation and computation

“…Particularly, the bands between 3297-3365 cm -1 , 2888-2945 cm -1 , and 1653 cm -1 , corresponded to O-H bonded with N-H stretching vibrations, C-H stretching vibrations, and C=O stretching vibrations in both carbohydrates and proteins ( Jia et al, 2017 , Wang et al, 2020b ). Besides, the peaks at 1457-1507 cm -1 , 1108-1128 cm -1 , and 1044-1054 cm -1 were assigned to N-H deformation vibrations, C-O-C, and C-H ring vibrations, respectively ( Chen et al, 2021 , Wang et al, 2020b ). The presence of characteristic functional groups in EPS-subtypes further suggested the involvement of hydrophobic protein and carbohydrate molecules, contributing to OT adsorption.…”

“…Additionally, the hydrophily degree of the EPS-subtypes in the 30 mg/L group exhibited 28.6%, 31.9%, and 22.2% less hydrophily in comparison with the control. Therefore, the OT-influenced higher EPS hydrophobicity promoted the formation of the OT-EPS aggregates, and the accelerated carbohydrate and protein secretions facilitated the bioadsorption ( Chen et al, 2021 ).…”