Responses of the MicroalgaChlorophytasp. to Bacterial Quorum Sensing Molecules (N-Acylhomoserine Lactones): Aromatic Protein-Induced Self-Aggregation

Abstract

Bacteria and microalgae often coexist during the recycling of microalgal bioresources in wastewater treatment processes. Although the bacteria may compete with the microalgae for nutrients, they could also facilitate microalgal harvesting by forming algal-bacterial aggregates. However, very little is known about interspecies interactions between bacteria and microalgae. In this study, we investigated the responses of a model microalga, Chlorophyta sp., to the typical quorum sensing (QS) molecules N-acylhomoserine lactones (AHLs) extracted from activated sludge bacteria. Chlorophyta sp. self-aggregated in 200 μm bioflocs by secreting 460-1000 kDa aromatic proteins upon interacting with AHLs, and the settling efficiency of Chlorophyta sp. reached as high as 41%. However, Chlorophyta sp. cells were essentially in a free suspension in the absence of AHLs. Fluorescence intensity of the aromatic proteins had significant (P < 0.05) relationship with the Chlorophyta sp. settleability, and showed a positive correlation, indicating that aromatic proteins helped aggregate microalga. Transcriptome results further revealed up-regulation of synthesis pathways for aromatic proteins from tyrosine and phenylalanine that was assisted by anthranilate accumulation. To the best of our knowledge, this is the first study to confirm that eukaryotic microorganisms can sense and respond to prokaryotic QS molecules.

Hormesis effects of phosphorus on the viability of Chlorella regularis cells under nitrogen limitation

“…Prior to the experiments, C. regularis was purified via the streaking plating method and preserved on agar jelly at 4 °C. Before the experiment, C. regularis was activated using classic BG11 medium under photoautotrophic condition [24]. As an inoculum of the experiment, the activated C. regularis cells were collected at the logarithmic phase (20 days of phototrophic cultivation) via centrifuging (6000× g for 5 min at 4 °C), and then washed and re-suspended three times with 0.9% sterile physiological saline.…”

Bacteria-mediated aggregation of the marine phytoplankton Thalassiosira weissflogii and Nannochloropsis oceanica

“…For example, some marine bacteria have specific flagellin genes (Winstanley & Morgan 1997), and adhesion genes in marine Flavobacteria (Fernández-Gómez et al 2013) might also play a role in the aggregation of phytoplankton cells. Quorum sensing (QS) has been documented in eukaryotic host-associated gram negative bacteria (Gram et al 2002;Rolland et al 2016;Zhou et al 2017), and mutations in the signalling molecule acyl-homoserine lactone (acyl-HSL) synthase in the bacterium Rhodobacter sphaeroides have led to hyper aggregation of cells in liquid culture (Puskas et al 1997). A similar QS phenotype was observed in the Gammaproteobacteria, Yersinia pseudotuberculosis where expression of a surface protein with homology to flagellin was thought to mediate aggregation (Atkinson et al 1999).…”

Stability and performance of algal-bacterial granular sludge in shaking photo-sequencing batch reactors with special focus on phosphorus accumulation

“…On the other hand, algae harvesting and separation from the treated water is challenging the promising algal-bacterial consortia systems due to the small size of microalgae cells (3-30 µm), poor settleability and low density (Zhou et al, 2017;Hu et al, 2017). Recently, there's a growing interest in the use of innovative solutions that combine microalgae technology with aerobic granular sludge (AGS) process, aiming to solve this problem.…”