Screening for the Heterotrophic Cultivation of Chlorella sorokiniana Using an Indirect Impedance Microbiological Technique

Balázs József Nagy,Áron Németh,Réka Czinkóczky

doi:10.3311/ppch.12864

Abstract

Heterotrophic culturing of microalgae is of great interest as it has the potential to produce feedstock for added-value bioproducts. The general expectation is to develop a method that can help screen for different media compositions and batch fermentation settings more easily and faster. In the current study, an indirect impedance microbiological technique was used to test the effects of various carbon and nitrogen sources on the growth of Chlorella sorokiniana. It was found that this technique has great potential to screen for heterotrophic cultivation conditions of microalgae as the metabolic rate of microorganisms can be determined by measuring the amount of CO2 produced. The BacTrac 4100® was proven to be a suitable instrument to compare several different small-scale culturing settings. Considering the relative changes in impedance observed, the initial cell cumber exhibits an inverse linear correlation with the detection time. Chlorella sorokiniana exhibited an enhanced degree of growth on yeast extract and tryptone, and preferred glucose over acetate or glycerol. An optimum rate of growth at a glucose concentration of 20 gL-1 was also determined. Our novel approach in the field of heterotrophic cultivation of microalgae envisages great prospects for the method in terms of the design of experiments in the field of media optimization.

Highlights

Chlorella species are the most studied strains of microalgae due to their high rates of growth and lipid productivity
While the biomass activity was to be measured via CO2 formation, it needs to be taken into consideration that CO2 is released under heterotrophic conditions (via central carbon metabolism, i.e. the tricarboxylic acid (TCA) cycle, glyoxylate cycle and pentose phosphate pathway (PPP) [21]), and is consumed under autotrophic conditions but under mixotrophic conditions its role is not fully understood
First the effect of the initial cell number was investigated, optimal nitrogen and carbon sources were selected, and two temperatures were compared on optimized media

Summary

Introduction

Chlorella species are the most studied strains of microalgae due to their high rates of growth and lipid productivity. Microalgae technology has been extensively tested at wastewater treatment facilities [6, 7]. In this respect, the thermotolerance of Chlorella sorokiniana attracts special attention with regard to the development of culturing technology, especially in terms of lipid production and biomass productivity. Chlorella sorokiniana grows well under autotrophic conditions, but higher concentrations of biomass have been reached under mixotrophic and heterotrophic conditions using glucose or acetate as a carbon source [11, 12]. Mixotrophic culturing can be 2.4-fold and 5.4-fold more effective in terms of biomass production than heterotrophic culturing and photoautotrophic culturing, respectively [13]

Methods

Results

Conclusion