Antifungal Activity of Bacillus Species Against Fusarium and Analysis of the Potential Mechanisms Used in Biocontrol

Abstract

Fusarium is a complex genus of ascomycete fungi that consists of plant pathogens of agricultural relevance. Controlling Fusarium infection in crops that leads to substantial yield losses is challenging. These economic losses along with environmental and human health concerns over the usage of chemicals in attaining disease control are shifting focus toward the use of biocontrol agents for effective control of phytopathogenic Fusarium spp. In the present study, an analysis of the plant-growth promoting (PGP) and biocontrol attributes of four bacilli (Bacillus simplex 30N-5, B. simplex 11, B. simplex 237, and B. subtilis 30VD-1) has been conducted. The production of cellulase, xylanase, pectinase, and chitinase in functional assays was studied, followed by in silico gene analysis of the PGP-related and biocontrol-associated genes. Of all the bacilli included in this study, B. subtilis 30VD-1 (30VD-1) demonstrated the most effective antagonism against Fusarium spp. under in vitro conditions. Additionally, 100 μg/ml of the crude 1-butanol extract of 30VD-1’s cell-free culture filtrate caused about 40% inhibition in radial growth of Fusarium spp. Pea seed bacterization with 30VD-1 led to considerable reduction in wilt severity in plants with about 35% increase in dry plant biomass over uninoculated plants growing in Fusarium-infested soil. Phase contrast microscopy demonstrated distortions and abnormal swellings in F. oxysporum hyphae on co-culturing with 30VD-1. The results suggest a multivariate mode of antagonism of 30VD-1 against phytopathogenic Fusarium spp., by producing chitinase, volatiles, and other antifungal molecules, the characterization of which is underway.

Diffusible and volatile organic compounds produced by avocado rhizobacteria exhibit antifungal effects against Fusarium kuroshium

“…The use of bacteria as biocontrol agents has gained interest since their potential to suppress diseases of various agricultural crops in a safe and eco-friendly way makes them viable alternatives to synthetic pesticides [40,41]. The biocontrol activity exerted by bacteria is carried out through numerous mechanisms, including the synthesis of hydrolytic enzymes, the production of diffusible and volatile compounds with antimicrobial activity, and the induction of systemic resistance (ISR) in the plant [42,43]. Several bacterial genera such as Bacillus, Pseudomonas, or Streptomyces, among others, have emerged as promising biological control agents of plant diseases caused by species of Fusarium [23,24,[44][45][46].…”

Impact of soil salinity on the cowpea nodule-microbiome and the isolation of halotolerant PGPR strains to promote plant growth under salinity stress

“…Both Pseudomonas and Bacillus have been reported as growth inhibitors for different fungal pathogens and provide protection against a number of plant diseases (Ali et al 2015; Shahid et al 2017; Khan et al 2017). More than one-half of the isolated strains especially members of Paenibacillus, Bacillus, Pseudomonas and Enterobacter , exhibited cellulase, chitinase, amylase, and protease activity, and a large number of PGPR strains ( Pseudomonas , Enterobacter, Rhizobium and Bacillus ) promote plant growth and suppress plant diseases by producing siderophores, hydrolytic enzymes, and HCN (Mehnaz et al 2010; Chen et al 2013; Khan et al 2018).…”

“…The antifungal activity of the bacterial isolates was observed using a dual-culture method where the test bacteria and the fungal culture are co-incubated on a potato dextrose agar (PDA; Sigma, USA) plate (Khan et al 2018). The antagonistic effectiveness of the test bacteria is assessed by measuring the inhibition of fungal mycelia around the bacteria.…”

Inoculation with a microbe isolated from the Negev Desert enhances corn growth

“…Physiological characterization of the selected strain was performed for various plant growth promotion abilities including the production of cellulase, pectinase, xylanase, and protease following standard protocols (Khan et al, 2018). Siderophore production and phosphate solubilization activity were tested on CAS agar and PVK plates respectively, following the methods described by Schwartz et al (2013).…”

“…The Dietzia cinnamea 55 genome was queried using IMG/MER (https://img.jgi.doe.gov/cgi-bin/er/main.cgi) against other sequenced Dietzia species and strains as well as other Gram-positive species including Micromonospora aurantiaca ATCC 27029 and L5 (Hirsch et al, 2013), Bacillus subtilis 30VD-1 (Khan et al, 2018), and B. simplex 30N-5 (Maymon et al, 2015) for plant-growth promoting traits such as phytohormone production, abiotic stress resistance, siderophore synthesis, and salinity tolerance. In addition, we queried the genomes for genes encoding virulence determinants such as the type VII secretion system (T7SS), which is frequently found in Gram-positive microbes, especially pathogenic species.…”