Abstract
Large-scale microalgae cultivations are increasingly used for the production of animal feed, nutritional supplements and various high-value bioproducts. Due to the process size and other limitations, contaminations of microalgae fermentations with other photoautotrophic microorganism are frequently observed. In the present study, we explored the applicability of 5-isobutyl-2,3-dimethylpyrazine for the removal of contaminating microalgae from industrial photobioreactors. In order to select a representative microbial population for susceptibility experiments, reactor samples were obtained from a multi-stage cultivation process. Assignments of 18S rRNA gene fragment amplicons indicated that Haematococcus, Chlorella, and Scenedesmus were the three most frequently occurring microalgae genera in the selected reactors. Following the isolation of representative algae cultures, susceptibility tests were conducted with the antimicrobial pyrazine. It was demonstrated that all isolated contaminants are highly susceptible to the bioactive compound. The highest tolerance towards the alkylpyrazine was observed with Scenedesmus vacuolatus; solutions with 1.66% (v/v) of the active compound were required for its deactivation. Further tests with the vaporized pyrazine showed consistent reductions in the viability of treated microalgae. This pilot study provides evidence for the applicability of a novel, nature-based alternative for bioreactor decontaminations.
Highlights
The industrial relevance of microalgae as production systems for valuable bioproducts and as promising feedstocks for biofuel production is constantly increasing[1,2,3]
Protista were represented by 73 operational taxonomic units (OTUs) (13.2%) and further identified as 23 different genera, whereby the most abundant genus was Ripella with a total amount of 28 OTUs and 160,259 reads; a total of 190,531 reads was assigned to Protista
The resolution of the obtained micrographs was not sufficient to provide information on changes of intracellular compartments. This is the first study to demonstrate the biocidal effect of alkylpyrazines on different microalgae species
Summary
The industrial relevance of microalgae as production systems for valuable bioproducts and as promising feedstocks for biofuel production is constantly increasing[1,2,3]. The production of high-valuable compounds from microalgae is mainly done on the basis of closed photobioreactors in order to reproduce production conditions, increase the control of cultivation variables and reduce the risk of contaminations[6,7]. Under both process conditions, one of the main constrains for an efficient cultivation of microalgae is the potential contamination with biological pollutants, such as bacteria, fungi, zooplankton or other undesirable microalgae[5,8,9,10]. These isolates showed high inhibition efficiency against plant pathogenic fungi, and the potential to inhibit potential human pathogens[20] These results imply that mimicking the bioactive volatilome of P. polymyxa is a promising strategy to control diverse microbial contaminations. In order to evaluate its applicability, the model pyrazine was evaluated by implementing two different application strategies that could find application in full-size bioreactors
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