Promoting Synechocystis sp. PCC 6803 Harvesting by Cationic Surfactants: Alkyl-Chain Length and Dose Control for the Release of Extracellular Polymeric Substances and Biomass Aggregation

Abstract

Development of an efficient biomass-harvesting technology for microalgae would achieve cost and energy savings in large-scale microalgae biomass cultivation. Cationic surfactants could improve biomass harvesting, but determining the optimal type and dose of surfactant requires mechanistic understanding. In this study, we evaluated how the alkyl-chain length and dose of three cationic surfactantshexadecyltrimethylammonium bromide (CTAB), myristyltrimethylammonium bromide (MTAB), and dodecyltrimethylammonium bromide (DTAB)affected biomass harvesting of Synechocystis. Flow cytometry (FC) with the nucleic-acid (NA) stain SYTOX Green (SG) was used to differentiate the release of extracellular polymeric substances (EPS) from cell lysis. All selected cationic surfactants dramatically improved the biomass-harvesting efficiency, and harvesting kinetics were represented well with a first-order kinetic model. The efficiency of biomass harvesting correlated positively with the alkyl-chain length; i.e., CTAB > MTAB > DTAB. A longer alkyl chain increased EPS release, which made it easier to achieve a less-negative zeta potential but without cell lysis. For CTAB, the largest cationic surfactant tested, a dose of 4.5 mM and treatment for 60 min achieved the maximum harvesting efficiency of ∼91%. This work lays the foundation for optimizing surfactant species and dose for biomass harvesting.

Sensitive and Accurate Differentiation of Extracellular Polymeric Substance Hydrolysis Using Flow Cytometry during Biofilm Extracellular Polymeric Substance Extraction

“…Thermal treatment significantly decreased cell size in the biofilm as SL continuously rose under increasing temperature. Strong and nearly linear relationships were observed between time and SL at 55 °C ( R 2 = 0.97, P < 0.01) and 60 °C in the initial 30 min ( R 2 = 0.95, P < 0.01); the SL increases and similar slopes (0.0023 and 0.0024) for the two linear fittings indicate the expected cell size decrease due to EPS release at low temperatures. , Longer time (≥30 min) at 60 °C led to a larger linear fitting slope of 0.0029, supporting the fact that the cell size decreased due to cell lysis. , A much higher temperature (>65 °C) led to sharply increased SL (0.0037–0.0040), which also had a nearly linear relationship with time ( R 2 > 0.98, P < 0.01) at all temperatures; this is an indication of decreased cell lysis …”

“…The SG-stained sample was diluted with 0.01 M PBS to obtain a suitable concentration that gave a count rate of 300–400 events/s. We counted 10,000 events for each biofilm sample in the FC (CytoFLEX, Beckman Coulter, American) . Data analysis and result outputs were realized using Flow Jo 10 software (Treestar, Inc., San Carlos, CA, USA).…”

“…14,47 In parallel, the peak with high FI shifted to the right with longer time at 60 °C, indicating that the cell membrane permeability was improved and SG dye can bind with intracellular NA. 33,45,48 For higher temperatures (>60 °C), the peak with high FI continuously shifted to the left with increasing time, a signal of the release of intracellular NA. 44,45 For CER extraction (Figure S21), the peaks were concentrated at 1100 FI units and remained stable at low stirring speeds (≤600 rpm).…”

Flocculation Efficiency and Mechanism of Carbamazepine by Microbial Flocculant Extracted from Klebsiella pneumoniae J1

“…In the first-order kinetics, the reaction rate is only proportional to the concentration of one reactant, while in the pseudo-first-order kinetics, the reaction rate is related to the concentration of the adsorbent and the adsorbate. When the concentration of one substance is much more than the other, it shows the characteristics of a first-order kinetic reaction [ 29 , 30 ].…”

Microalgae Biomolecules: Extraction, Separation and Purification Methods

“…The most commonly used surfactants are long-chain alkyl groups (C12 to C16) containing quaternary-ammonium cation. These compounds have hydrophobic ends capable of adsorbing or attaching to cell membranes, and once this happens, the quaternary cation makes the cell charge to become less negative, favoring cell aggregation [57]. Lai et al [58] evaluated this synergistic effect by using cationic surfactants for flocculation and lipid extraction from C. vulgaris.…”