Estibaliz Sansinenea

Secondary metabolites of soil Bacillus spp.

Bacillus species produce secondary metabolites that are the object of natural product chemistry studies. The wide structural variability of these compounds has attracted the curiosity of chemists and their biological activities have inspired the pharmaceutical industry to search for lead structures in microbial extracts. Screening of microbial extracts reveals the large structural diversity of natural compounds with broad biological activities, such as antimicrobial, antiviral, immunosuppressive, and antitumor activities, that enable the bacterium to survive in its natural environment. These findings widen the potential industrial importance of Bacillus spp., particularly of B. thuringiensis, beyond insecticidal usage and may help explain the role of Bacillus spp. in the soil ecosystem.

The synthetic versatility of oxazolidinethiones

Different methods for the preparation of oxazolidinethiones and their more recent applications are reviewed. In this review, novel rearrangements and new reactions have also been summarized which for their homologous oxazolidinones have not been observed. The principal application of oxazolidinethiones has been as chiral auxiliaries in asymmetric aldol addition reactions for the obtention of chiral fragments containing one or two stereogenic centres with the stereochemistry required for the preparation of complex natural products.

Genetic manipulation in Bacillus thuringiensis for strain improvement

Bacillus thuringiensis (Bt) has been used as a biopesticide in agriculture, forestry and mosquito control because of its advantages of specific toxicity against target insects, lack of polluting residues and safety to non-target organisms. The insecticidal properties of this bacterium are due to insecticidal proteins produced during sporulation. Despite these ecological benefits, the use of Bt biopesticides has lagged behind the synthetic chemicals. Genetic improvement of Bt natural strains, in particular Bt recombination, offers a promising means of improving efficacy and cost-effectiveness of Bt-based bioinsecticide products to develop new biotechnological applications.

An Ultra-Violet Tolerant Wild-Type Strain of Melanin-Producing Bacillus thuringiensis

Background: Bacillus thuringiensis is the most successful biological control agent used in agriculture, forestry and mosquito control. However, the insecticidal activity of the B. thuringiensis formulation is not very stable and rapidly loses its biological activity under field conditions, due to the ultraviolet radiation in sunlight. Melanin is known to absorb radiation therefore photo protection of B. thuringiensis based on melanin has been extensively studied. Objectives: The aim of this study was to find a wild type strain of naturally melanin-producing B. thuringiensis to avoid any mutation or manipulation that can affect the Cry protein content. Materials and Methods: Bacillus thuringiensis strains were isolated from soils of different States of Mexico and pigment extraction was followed by lowering the pH to 2 using 1N HCl. Pigment was characterized by some chemical tests based on its solubility, bleaching by H2O2 and flocculation with FeCl3, and using an Infrared (IR) spectrum. Ultraviolet (UV) irradiation experiment was performed to probe the melanin efficacy. Results: ELI52 strain of B. thuringiensis was confirmed to naturally produce melanin. The Cry protein analysis suggested that ELI52 is probably a B. thuringiensis subsp. israelensis strain with toxic activity against the Diptera order of insects. Ultra Violet protection efficacy of melanin was probed counting total viable colonies after UV radiation and comparing the results with the non-producing melanin strain L-DOPA (L-3, 4-dihydroxyphenylalanine) was also detected in the culture. ELI52 strain showed an antagonistic effect over some common bacteria from the environment. Conclusions: ELI52 wild-type strain of B. thuringiensis is a good bio-insecticide that produces melanin with UV-resistance that is probably toxic against the Diptera order of insects and can inhibit the growth of other environmental bacteria.

Discovery and Description of Bacillus thuringiensis

The use of biopesticides, as a component of integrated pest management (IPM), has been gaining acceptance over the world. An entomopathogenic organism should be highly specific and effective against the target pest and should demonstrate the potential to be successfully processed by continuous production technology. Bacillus thuringiensis (Bt) was discovered as a soil bacterium, which fulfills all these requirements and due to it has been used as a biopesticide in agriculture, forestry and mosquito control. Studies of the basic biology of Bt have shown that the insecticidal activity of Bt is due to the presence of parasporal protein inclusion bodies, also called crystals, produced during sporulation that determines its activity for insect species belonging to different orders, which act like a stomach poison causing larval death. Environmentally safe-insect control strategies based on Bt and their insecticidal crystal proteins are going to increase in the future, especially with the wide adoption of transgenic crops. In this chapter, I have summarized the discovery and the description of Bt.

Melanin: a photoprotection for Bacillus thuringiensis based biopesticides

Melanins are negatively-charged, hydrophobic, dark high molecular weight irregular biopolymers, composed of polymerized phenolic and/or indolic compounds. They are produced by most organisms. Bacillus thuringiensis is a Gram-positive, spore-forming, soil bacterium and the most successful biological control agent that produces distinctly shaped crystals during sporulation that have insecticidal activity. However, one of the main disadvantages is that the insecticidal activity of B. thuringiensis formulation is unstable and rapidly loses its activity under field conditions due to UV radiation. Melanin absorbs radiation; therefore photoprotection of B. thuringiensis based on melanin has been studied and is herewith reviewed.

Characterisation of two novel bacteriocin-like substances produced by Bacillus amyloliquefaciens ELI149 with broad-spectrum antimicrobial activity

OBJECTIVES The aim of this study was to isolate and characterise antifungal and bactericidal compounds from Bacillus amyloliquefaciens strain ELI149. METHODS An absorbent resin (Amberlite® XAD-16) and silica gel column chromatography were used for isolation and purification purposes, respectively. Antibacterial and antifungal assays were performed by the well diffusion method to demonstrate the biological activity of each compound. Cell damage of the tested fungi was evaluated for fengycin under phase-contrast microscopy. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and mass spectroscopy techniques were performed to estimate the approximate molecular mass of each compound. RESULTS Two bacteriocin-like substances (BLSs) with different physical properties and inhibitory activities were isolated along with two known antifungal compounds. The two BLSs were heat stable and were not sensitive to acid or alkaline conditions (pH 2-10), with broad-spectrum antimicrobial activity. The antifungal compounds were identified as surfactin and fengycin. Only fengycin showed marked antifungal properties against several phytopathogens. CONCLUSIONS The two isolated BLSs were partially characterised and their bactericidal properties were analysed. The antifungals compounds were identified as surfactin and fengycin, this latter being mainly responsible for the antifungal activity.

Cellular damage of plant pathogenic fungi by antifungal compounds produced by Bacillus spp. isolates

ABSTRACT The use of microorganisms as biological control agents (BCAs) has become an effective alternative to chemical means of controlling plant pathogens. The antagonistic and inhibitory activity of 71 Bacillus spp. strains, which were isolated from different Mexican sites, were tested against several phytopathogen fungi, Fusarium oxysporum, Fusarium equiseti, Fusarium avenaceum, Bipolaris spp. and Alternaria spp. From the antagonism study, the strain ELI149 showed a marked inhibition of growth against all tested fungi; therefore crude metabolites from this strain were extracted using ethyl acetate and amberlite resin and probed against the same fungi as well as strains of Mucor sp., Penicillium spp. and Paecilomyces spp. The results indicated that amberlite was more suitable for extraction of secondary metabolites with antifungal activity. Finally, observation of cell damage in the tested pathogenic fungi showed marked morphological changes on reproductive structures in all tested fungi indicating that antibiosis was the mechanism of the antagonistic effect. These results suggest that metabolites from the Bacillus strains have a wide spectrum of antibiotic activities, which can be used as biocontrol agents for controlling fungal plant diseases of agricultural importance.

Di-2-ethylhexylphthalate May Be a Natural Product, Rather than a Pollutant

Di-2-ethylhexylphtalate is an ester of phthalic acid that has been used as plasticizer in many materials. Due to the extended use, it has been persistently found in different environments being classified as a pollutant with some risks for human health. However, in the last years, it has been found that this compound is produced by plants or microorganisms like bacteria or fungi. This finding opened a serious debate about the origin of this compound and questioned if it is a real pollutant or a natural metabolite with some biological activities that could help us in several ways. This review tries to give some data of the different points of view about this question.

3,4-Dihydroisocoumarins, interesting natural products: isolation, organic syntheses and biological activities

BACKGROUND 3,4-dihydroisocoumarins are an important small group belonging to the class of naturally occurring lactones isolated from different bacterial strains, molds, lichens, and plants. The structures of these natural compounds show various types of substitution in their basic skeleton and this variability influences deeply their biological activities. These lactones are structural subunits of several natural products and serve as useful intermediates in the synthesis of different heterocyclic molecules, which exhibit a wide range of biological activities, such as anti-inflammatory, antiplasmodial, antifungal, antimicrobial, antiangiogenic and antitumoral activities, among others. Their syntheses have attracted attention of many researchers reporting many synthetic strategies to achieve 3,4-dihydroisocoumarins and other related structures. OBJECTIVE In this context, the isolation of these natural compounds from different sources, their syntheses and biological activities are reviewed, adding the most recent advances and related developments. CONCLUSION This review aims to encourage further work on the isolation and synthesis of this class of natural products. It would be beneficial for synthetic as well as the medicinal chemists to design selective, optimized dihydroisocoumarin derivatives as potential drug candidates, since dihydroisocoumarin scaffolds have significant utility in the development of therapeutically relevant and biologically active compounds.