Formalin-casein enhances water absorbency of calcium alginate beads and activity of encapsulated Metarhizium brunneum and Saccharomyces cerevisiae

Katharina M Hermann,Alexander Grünberger,Anant V Patel

doi:10.1007/s11274-021-03121-3

Katharina M Hermann, Alexander Grünberger + Show 1 more

Open Access

https://doi.org/10.1007/s11274-021-03121-3

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Abstract

The control of root-feeding wireworms has become more challenging as synthetic soil insecticides have been progressively phased out due to environmental risk concerns. Innovative microbial control alternatives such as the so-called attract-and-kill strategy depend on the rapid and successful development of dried encapsulated microorganisms, which is initiated by rehydration. Casein is a functional additive that is already used in food or pharmaceutical industry due to its water binding capacity. Cross-linked forms such as formalin-casein (FC), exhibit altered network structures. To determine whether FC influences the rehydration of alginate beads in order to increase the efficacy of an attract-and-kill formulation for wireworm pest control, we incorporated either casein or FC in different alginate/starch formulations. We investigated the porous properties of alginate/starch beads and subsequently evaluated the activities of the encapsulated entomopathogenic fungus Metarhizium brunneum and the CO2 producing yeast Saccharomyces cerevisiae. Adding caseins altered the porous structure of beads. FC decreased the bead density from (1.0197 ± 0.0008) g/mL to (1.0144 ± 0.0008) g/mL and the pore diameter by 31%. In contrast to casein, FC enhanced the water absorbency of alginate/starch beads by 40%. Furthermore, incorporating FC quadrupled the spore density on beads containing M. brunneum and S. cerevisiae, and simultaneous venting increased the spore density even by a factor of 18. Moreover, FC increased the total CO2 produced by M. brunneum and S. cerevisiae by 29%. Thus, our findings suggest that rehydration is enhanced by larger capillaries, resulting in an increased water absorption capacity. Our data further suggest that gas exchange is improved by FC. Therefore, our results indicate that FC enhances the fungal activity of both fungi M. brunneum and S. cerevisiae, presumably leading to an enhanced attract-and-kill efficacy for pest control.Graphic abstract

Highlights

Wireworms (Coleoptera: Elateridae) are widespread pests that damage a variety of crops, including grain i.e. wheat, barley, maize and most vegetables such as carrot and potato
We found that FC influences the porous properties of alginate/starch beads, enhancing their water absorbency
FC increases the fungal activity of encapsulated M. brunneum and S. cerevisiae, leading to enhanced spore formation and CO2 productivity

Summary

Introduction

Wireworms (Coleoptera: Elateridae) are widespread pests that damage a variety of crops, including grain i.e. wheat, barley, maize and most vegetables such as carrot and potato. Since the mid-twentieth century wireworm damage is becoming an increasing concern in both conventional and organic potato cultivation (Poggi et al 2018; Vernon and van Herk 2013). Wireworms can be very destructive and difficult to control. Effective plant protection products are currently not available, since chemical insecticides have been restricted or abandoned. Neonicotinoids and fipronil were the main classes of insecticides routinely used and both have been restricted by the European Union (European Food Safety Authority 2013). There is a tremendous need for control options, either conventional, or better yet, biological such as microbial pest control

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