Plant Pellets: A Compatible Vegan Feedstock for Preparation of Plant-Based Culture Media and Production of Value-Added Biomass of Rhizobia

Hassan-Sibroe A Daanaa,Nabil A Hegazi,Hanan A Goda,Reem Hamed,Mohamed Fayez,Mahmoud El-Tahan,Mervat A Hamza,Mennatullah Abdou,Hanan H Youssef,Mohamed T Abbas,Silke Ruppel,Mohamed S Sarhan

doi:10.3390/su12208389

Abstract

Although plant-based culture media enhances in vitro cultivation of rhizobacteria, studies assessing their biomass potential for large-scale applications are lacking. Here, we advance plant pellets (PPs) as a novel technology to unlock the potential of such vegan culture media for biomass production of Rhizobium leguminosarum. PP formulations were based on mixtures of Egyptian clover powder and the agro-byproducts glycerol and molasses. These mixtures were either contained or not contained in teabags during culture media preparation. Metrics of biomass included colony forming units, optical density (OD600nm), and cell dry weight (DW). Biomass comparisons between culture media based on PPs and standard yeast extract mannitol (YEM) revealed that the following PPs composition, contained in teabags, cultivated rhizobia at levels comparable to YEM: 16 g clover powder, 5% molasses, and 0.8% glycerol. This PPs composition enabled shorter generation times of rhizobia (PP: 3.83 h, YEM: 4.28 h). Strikingly, PPs mixtures supplemented with 10% molasses and not contained in teabags promoted rhizobia without apparent lag phases and produced 25% greater DW than YEM. PPs potentiate the use of dehydrated vegan feedstocks for both plant microbiota cultivation and biomass production and appear as cost- and labor-effective tools, easy to handle and store for plant-based culture media preparation.

Highlights

The plant microbiome plays a pivotal role in enhancing plant health and nutrition
Introductory experiments were carried out to assess the growth and biomass production of R. leguminosarum on culture media formulated from clover powder and/or clover powder supplemented with the agro-byproducts, glycerol and molasses
The present study encourages a new line of research focusing on the use of plant pellets as a vegan feedstock for value-added biomass production of rhizobacteria

Summary

Introduction

The plant microbiome plays a pivotal role in enhancing plant health and nutrition. Here, the plant root exudates, rich in organic acids and proteins, enable mutually beneficial interactions between microbial consortia and their host plants [1,2,3,4,5,6]. Other members of Pseudomonas spp., Azospirillum spp., Azotobacter spp., and Enterobacter spp. are involved in nitrogen fixation through associated and/or asymbiotic interactions [14] Members of these genera (including rhizobia) include phytostimulatory agents that secrete—e.g., indole acetic acid and ACC deaminase—and/or mobilize elements such as P, K, and Fe absorbed by plants [14,15]. Given these features of agro-biopreparates (bio-fertilizers and bio-pesticides), their large-scale cultivation and application has become a central agro-biotechnological tool supporting the productivity of economically important crops, especially staple food sources [14,16]. PGPRs are vital bioresources towards the end goal of satisfying global food demand [17,18]

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Conclusion