Valorization of Lignin as an Immobilizing Agent for Bioinoculant Production using Azospirillum brasilense as a Model Bacteria

Abstract

Plant growth-promoting bacteria (PGPB) have been largely considered as beneficial in harsh and limiting environments given their effects on alleviating plant stress. For practical applications, most of the PGPB are prepared in immobilization matrices to improve the stability and benefits of bacteria. Despite the long list of immobilizing agents/carriers tested to date, a long list of desired requirements is yet to be achieved. Here, lignin stands as a scarcely tested immobilizer for bioinoculants with great potential for this purpose. The aim of this work was to demonstrate the feasibility of lignin as a carrier of the nitrogen-fixing Azospirillum brasilense. These bacteria were cultured in liquid media with recovered organosolv lignin added for bacterial immobilization. Then, lignin was recovered and the immobilized biomass was quantified gravimetrically by DNA extraction and serial dilution plating. Fluorescent microscopy as well as Congo red agar plating showed the immobilization of the bacterial cells in the lignin matrix and crystal violet dyeing showed the biofilms formation in lignin particles. A high number of cells were counted per gram of dried lignin. Lignin can be readily used as low-cost, health-safe bioinoculant carrier to be used in soil and agricultural applications.

Silica/Lignin Carrier as a Factor Increasing the Process Performance and Genetic Diversity of Microbial Communities in Laboratory-Scale Anaerobic Digesters

“…This finding is connected to both the presence of nutrients, carbohydrates and available forms of nitrogen (see Tables 1 and 3) and the carrier, which, thanks to its adsorption properties, provided an ideal habitat for the growth of the autochthonous microbiome [12,23]. The study by Tapia-Olivares et al (2019) demonstrates that lignin, as a non-toxic, efficient and above all, renewable organic resource, is an excellent carrier for bacteria [53], as is silica which increases the adhesion of microorganisms and their stability and dispersion in culture fluids [54].…”