Biocontrol of Aspergillus Species on Peanut Kernels by Antifungal Diketopiperazine Producing Bacillus cereus Associated with Entomopathogenic Nematode

Abstract

The rhabditid entomopathogenic nematode associated Bacillus cereus and the antifungal compounds produced by this bacterium were evaluated for their activity in reducing postharvest decay of peanut kernels caused by Aspergillus species in in vitro and in vivo tests. The results showed that B. cereus had a significant effect on biocontrol effectiveness in in vitro and in vivo conditions. The antifungal compounds produced by the B. cereus were purified using silica gel column chromatography and their structure was elucidated using extensive spectral analyses. The compounds were identified as diketopiperazines (DKPs) [cyclo-(L-Pro-Gly), cyclo(L-Tyr-L-Tyr), cyclo-(L-Phe-Gly) and cyclo(4-hydroxy-L-Pro-L-Trp)]. The antifungal activities of diketopiperazines were studied against five Aspergillus species and best MIC of 2 µg/ml was recorded against A. flavus by cyclo(4-hydroxy-L-Pro-L-Trp). To investigate the potential application of cyclo(4-hydroxy-L-Pro-L-Trp) to eliminate fungal spoilage in food and feed, peanut kernels was used as a food model system. White mycelia and dark/pale green spores of Aspergillus species were observed in the control peanut kernels after 2 days incubation. However the fungal growth was not observed in peanut kernels treated with cyclo(4-hydroxy-L-Pro-L-Trp). The cyclo(4-hydroxy-L-Pro-L-Trp) was nontoxic to two normal cell lines [fore skin (FS) normal fibroblast and African green monkey kidney (VERO)] up to 200 µg/ml in MTT assay. Thus the cyclo(4-hydroxy-L-Pro-L-Trp) identified in this study may be a promising alternative to chemical preservatives as a potential biopreservative agent which prevent fungal growth in food and feed. To the best of our knowledge, this is the first report demonstrating that the entomopathogenic nematode associated B. cereus and cyclo(4-hydroxy-L-Pro-L-Trp) could be used as a biocontrol agents against postharvest fungal disease caused by Aspergillus species.

Draft Genome Sequence of <b><i>Bacillus cereus</i></b> CITVM-11.1, a Strain Exhibiting Interesting Antifungal Activities

“…This strain exhibited strong antagonistic activity in vitro to the charcoal root rot fungus Macro phomina phaseolina, by causing the inhibition of hyphal development and impaired the formation of sclerotia [Felipe et al, 2017]. This finding was consistent with those about other B. cereus strains that have demonstrated their potential for the biocontrol of some phytopathogenic fungi, bacteria, and plant-parasitic nematodes, in both in vitro assays and in vivo trials [Kumar et al, 2014b;Martinez-Alvarez et al, 2016].…”

“…Nevertheless, several strains of this species have demonstrated potential to be used as plant growth-promoting rhizobacteria (PGPR), since they are capable of exhibiting antagonistic activities against several phytopathogenic microorganisms [Kumar et al, 2014b] and inducing plant systemic resistance against phytopathogenic bacteria such as Pseudomonas syringae [Niu et al, 2011].…”

Effects of Interactions of Auxin-Producing Bacteria and Bacterial-Feeding Nematodes on Regulation of Peanut Growths

“…And some of these bacteria have nematicidal potentials and can confer protection against root-knot nematode infections [ 37 , 38 ]. Bacillus species associated with entomopathogenic nematodes may be used as biocontrol agents against postharvest fungal disease [ 39 ]. Therefore, in addition to the plant growth-promoting effects of Bacillus , its interactions with nematodes require further research.…”

Antibacterial activity of cyclo(L-Pro-L-Tyr) and cyclo(D-Pro-L-Tyr) from Streptomyces sp. strain 22-4 against phytopathogenic bacteria

“…This can be seen from a chitinase producing Streptomyces glauciniger WICC-A03 (Awad et al 2014) or a related compound, cyclo(4-hydroxy-L-Pro-L-Trp) which has already been deployed as a nontoxic biopreservative agent to inhibit the growth of A. flavus and A. niger on peanut kernels (Kumar et al 2014). With further toxicity testing and structure modification to improve the biological activity of cyclo(Pro-Tyr), this cyclic dipeptide may be a promising biocontrol agent for use in the agricultural industry.…”