Isolation and Identification of Antibacterial Bioactive Compounds From Bacillus megaterium L2

Yudan Xie,Qiuju Peng,Jinyi Zhao,Ailin Xie,Yang Xiao,Tengxia He,Yuyu Ji,Qinyu Zhang,Long Yang,Zhu Li,Shuzhen Mu

doi:10.3389/fmicb.2021.645484

Abstract

Bacterial metabolites exhibit a variety of biologically active compounds including antibacterial and antifungal activities. It is well known that Bacillus is considered to be a promising source of bioactive secondary metabolites. Most plant pathogens have an incredible ability to mutate and acquire resistance, causing major economic losses in the agricultural field. Therefore, it is necessary to use the natural antibacterial compounds in microbes to control plant pathogens. This study was conducted to investigate the bio-active compounds of Bacillus megaterium L2. According to the activity guidance of Agrobacterium tumefaciens T-37, Erwinia carotovora EC-1 and Ralstonia solanacearum RS-2, five monomeric compounds, including erucamide (1), behenic acid (2), palmitic acid (3), phenylacetic acid (4), and β-sitosterol (5), were fractionated and purified from the crude ethyl acetate extract of B. megaterium. To our knowledge, all compounds were isolated from the bacterium for the first time. To understand the antimicrobial activity of these compounds, and their minimum inhibitory concentrations (MICs) (range: 0.98∼500 μg/mL) were determined by the broth microdilution method. For the three tested pathogens, palmitic acid exhibited almost no antibacterial activity (>500 μg/mL), while erucamide had moderate antibacterial activity (MIC = 500 μg/mL). Behenic acid showed MICs of 250 μg/mL against T-37 and RS-2 strains with an antibacterial activity. β-sitosterol showed significant antimicrobial activity against RS-2. β-sitosterol showed remarkable antimicrobial activity against RS-2 with an MIC of 15.6 μg/mL. In addition, with the antimicrobial activity, against T-37 (62.5 μg/mL) and against EC-1 (125 μg/mL) and RS-2 (15.6 μg/mL) strains notably, phenylacetic acid may be interesting for the prevention and control of phytopathogenic bacteria. Our findings suggest that isolated compounds such as behenic acid, β-sitosterol, and phenylacetic acid may be promising candidates for natural antimicrobial agents.

Highlights

Increasing use of chemical pesticides to combat a variety of plant diseases has resulted in heavy soil pollution in recent years (Munoz-Leoz et al, 2013)
The inhibition rate of the n-butanol phase was more than 50% against T-37 and EC-1
We found that no antibacterial activity was exhibited by palmitic acid (MIC > 500 μg/mL), suggesting that the compound is not considered as an antimicrobial agent for the tested plant pathogenic bacteria

Summary

Introduction

Increasing use of chemical pesticides to combat a variety of plant diseases has resulted in heavy soil pollution in recent years (Munoz-Leoz et al, 2013). Biological control agents can act as a pathogen-specific, safe, and pollutionfree alternative to chemicals that have negative effects on the environment and animal and human health (Goulson, 2014; Nicolopoulou-Stamati et al, 2016). Natural resources such as microorganisms, plants, and animals are used to extract novel compounds, of which microbes are a major source for finding new antimicrobial agents. Bacillus megaterium is a rich source of metabolites, which is well-known to produce metabolites with antibacterial and antifungal activities (AlThubiani et al, 2018; Mannaa and Kim, 2018). B. megaterium can synthesize vitamin B12 through an oxygen-independent adenosylcobalamin pathway (Eppinger et al, 2011)

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