Morphological characterization of Cupriavidus necator DSM 545 flocs through image analysis

Abstract

Flocculating agents are used as auxiliary to recover bacterial cells in downstream processes for polyhydroxyalkanoate production. However little is known about the Curpiavidus necator flocs. In this work a new procedure for floc characterization through digital image analysis is presented and validated using the batch settling test. Average diameter, particle size distribution and morphological characteristics of the microbial aggregates were obtained from the flocculation/sedimentation process of the Cupriavidus necator DSM 545 cells by the use of tannin as flocculating agent. The experimental results demonstrated that the proposed method is adequate to determine the average floc diameter with values around 150 μm in accordance with the value obtained from the batch settling test. Nevertheless a morphological characterization of Cupriavidus necator DSM 545 bioaggregates in terms of size distribution and regularity could only be performed by an image analysis procedure. The procedure allowed us to describe the regularity of bacterial flocs through the quantification of morphological parameters of Euclidean [convexity (Conv) and form factor (FF)] and fractal geometry [surface fractal dimension (D BS)], which are important factors to be considered in the settling efficiency of aggregates.