Zeolite-based, dry formulations for conservation and practical application of Paraburkholderia phytofirmans PsJN

Abstract

Aims: Producing dry, zeolite-based granular and powder inoculants of the Gram-negative, plant growth-promoting bacterium Paraburkholderia phytofirmans PsJN. Key aspects were maintenance of cell viability during desiccation and throughout storage at ambient conditions.

Methods and results: Twenty additives and exopolysaccharide (EPS) produced by PsJN were screened for conserving cell viability of PsJN in air-drying and lyophilization. Suitable combinations (e.g. skimmed milk + air-drying) increased survival of PsJN up to 100 000-fold and maintained it for >7 months. EPS performed as good as skimmed milk during air-drying, but was second-rank regarding shelf life. Combinations of zeolite, skimmed milk and gelatin as a film-forming agent were extruded and processed into granules and powders, both displaying relatively stable viability for over 4 weeks at ambient conditions. Gelatin promoted brittleness of zeolite-based inoculants.

Conclusions: Viability of highly sensitive PsJN was successfully conserved in dry formulations, taking into account the interplay between carrier, protectants, drying method and coating agent.

Significance and impact of the study: This is the first study to provide ways of maintaining viability of PsJN during desiccation stress and to investigate the applicability of its EPS as a protectant, thus ultimately facilitating successful plant inoculation especially under field conditions.

Keywords: Paraburkholderia phytofirmans PsJN; desiccation; exopolysaccharide; formulation; zeolite.