Screening of liquid media and fermentation of an endophytic Beauveria bassiana strain in a bioreactor.

Rieke Lohse,Anant V Patel,Desiree Jakobs-Schönwandt

doi:10.1186/s13568-014-0047-6

Abstract

A novel approach for biological control of insect pests could be the use of the endophytic entomopathogenic Beauveria bassiana isolate ATP-02. For the utilization of the endophyte as a commercial biocontrol agent, the fungus has to be mass-produced. B. bassiana was raised in shake flask cultures to produce high concentrations of total spores (TS), which include blastospores (BS) and submerged conidiospores (SCS). The highest concentration of 1.33×109 TS/mL and the highest yield of 5.32×1010 TS/g sucrose was obtained in the TKI broth with 5% sugar beet molasses which consists of 50% sucrose as a carbon source. In spite of the lower sugar concentration (2.5%) the amount of TS could be increased up to 11-times in contrast to the cultivation with 5% sucrose. The scale-up to a 2 L stirred tank reactor was carried out at 25°C, 200–600 rpm and 1 vvm at pH 5.5. A TS yield of 5.2×1010 TS/g sucrose corresponding to a SCS yield of 0.2×1010 SCS/g sucrose was obtained after 216 h. With regards to the culture medium the cost of 1012 TS amounts to 0.24 €. Plutella xylostella larvae, which were fed with oilseed rape leaves treated with spores from fermentation resulted in 77 ± 5% mortality. Moreover, spores from submerged cultivation were able to colonize oilseed rape leaves via leaf application. This is the first report of fermentation of an endophytic B. bassiana strain in a low-cost culture medium to very high yields of TS.

Highlights

In the past decades, many microorganisms have been isolated and investigated for use as a biocontrol agent
This study deals with the fermentation aspects of the endophytic B. bassiana ATP-02 which might prepare the way to exploit endophytes as commercial biocontrol agents
Screening of media in shake flask culture In the past, mass-production of B. bassiana has focused on aerial conidia (AC), but the production through surface cultivation or a two-stage process in which the fungus is allowed to develop under submerged conditions and subsequently transferred to a solid media to sporulate requires long cultivation times, large amounts of space and can be labour-intensive (Hall and Papierok 1982)

Summary

Introduction

Many microorganisms have been isolated and investigated for use as a biocontrol agent. Endophytic B. bassiana strains can exist asymptomatically in a variety of plants like banana (Akello et al 2008), opium poppies (Quesada-Moraga et al 2006), maize (Bing and Lewis 1992) and sorghum (Tefera and Vidal 2009). The recently isolated endophytic B. bassiana strain ATP-02 showed great potential for a novel plant control measure in a variety of crops (Tefera and Vidal 2009). It remained unknown if this strain can be mass-produced to high yields and if the spores from a submerged fermentation are able to colonize plants. The virulence of the produced spores was checked in a bioassay with Plutella xylostella and their potential to colonize oilseed rape leaves via a leaf application was investigated

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