Isolation of a new Mexican strain of Bacillus subtilis with antifungal and antibacterial activities

The Prospect of Hydrolytic Enzymes from Bacillus Species in the Biological Control of Pests and Diseases in Forest and Fruit Tree Production

Plant diseases and insect pest damage cause tremendous losses in forestry and fruit tree production. Even though chemical pesticides have been effective in the control of plant diseases and insect pests for several decades, they are increasingly becoming undesirable due to their toxic residues that affect human life, animals, and the environment, as well as the growing challenge of pesticide resistance. In this study, we review the potential of hydrolytic enzymes from Bacillus species such as chitinases, β-1,3-glucanases, proteases, lipases, amylases, and cellulases in the biological control of phytopathogens and insect pests, which could be a more sustainable alternative to chemical pesticides. This study highlights the application potential of the hydrolytic enzymes from different Bacillus sp. as effective biocontrol alternatives against phytopathogens/insect pests through the degradation of cell wall/insect cuticles, which are mainly composed of structural polysaccharides like chitins, β-glucans, glycoproteins, and lipids. This study demonstrates the prospects for applying hydrolytic enzymes from Bacillus sp. as effective biopesticides in forest and fruit tree production, their mode of biocidal activity and dual antimicrobial/insecticidal potential, which indicates a great prospect for the simultaneous biocontrol of pests/diseases. Further research should focus on optimizing the production of hydrolytic enzymes, and the antimicrobial/insecticidal synergism of different Bacillus sp. which could facilitate the simultaneous biocontrol of pests and diseases in forest and fruit tree production.

Activity of Aqueous Extracts from Native Plants of the Yucatan Peninsula against Fungal Pathogens of Tomato In Vitro and from Croton chichenensis against Corynespora cassiicola on Tomato

Plant extracts are a valuable alternative to control pathogens of horticultural crops. In the present study, four species of pathogenic fungi were isolated from leaf spots on Solanum lycopersicum and identified by traditional and molecular techniques as Alternaria alternata ITC24, Corynespora cassiicola ITC23, Curvularia lunata ITC22, and Fusarium equiseti ITC32. When 11 aqueous extracts from eight native plants of the Yucatan Peninsula were tested against the four fungi in vitro, the extract from Croton chichenensis roots was most active, inhibiting mycelial growth (79-100%), sporulation (100%), and conidial germination (71-100%) at 3% (w/v). A logarithmic-diagrammatic scale of the pathosystem C. cassiicola-S. lycopersicum was established and used to assess disease severity on inoculated tomato plants in a greenhouse after treatment with the aqueous extract from C. chichenensis roots at 12% (w/v). After 21 days, the disease severity was 57% lower than on the control without extract applied. This dose of the extract was not phytotoxic to tomato leaves and was compatible with the beneficial organisms Bacillus subtilis CBCK47 and Trichodema asperellum Ta13-17. The antifungal efficacy of C. chichenensis is highly promising for incorporation into integrated disease management of tomato crops.

Non-Rhizobial Endophytes Associated with Nodules of Vigna radiata L. and Their Combined Activity with Rhizobium sp

Root nodules of legume plants are devoted for hosting endophytic symbiotic bacteria that fix atmospheric nitrogen but recently proved as a niche for various non-rhizobial endophytes (NRE) also. In the present investigation, one rhizobial and two NRE were isolated and characterized as Rhizobium sp. AAU B3, Bacillus sp. AAU B6 and Bacillus sp. AAU B12. These isolates were studied for in vitro biocontrol activity against two pathogenic fungi. NRE isolates exhibited antifungal activity against root rot causing Macrophomina phaseolina (ITCC-6749) isolated from Vigna radiata and wilt causing pathogen Fusarium udum Butler isolated from Cajanus cajan in liquid as well as on solid medium. Furthermore, their antagonism was increased markedly when combined with Rhizobium sp. Moreover, Bacillus sp. AAU B6 showed amplification of the zwittermicin A gene (~ 950 bp) which is evident for the production of antibiotics. All three isolates showed HCN production in vitro also, Bacillus sp. AAU B12 exhibited amplification of its gene hcnC. Pathogenic fungal hyphae became thin, transparent, and bent as well as fungi lost their normal growth and branching patterns when exposed to volatile compounds produced by NRE. All the 3 isolates produced siderophores, however siderophore production was increased considerably when all three strains are mixed together. Furthermore, all the three isolates produced cell wall degrading enzymes (chitinase, protease, and cellulase) but lipolytic activity was exhibited only by Rhizobium sp. AAU B3. When NRE inoculated in combination of Rhizobium; overcomes the disease severity against M. phaseolina under pot study. Thus, from present study it is concluded that co-inoculation of NRE and Rhizobium sp. can be exploited as biocontrol bio-agents against M. phaseolina in green gram at field levels.

Endophytic Bacteria Bacillus subtilis, Isolated from Zea mays, as Potential Biocontrol Agent against Botrytis cinerea

Simple Summary

Plant–microorganism associations date back more than 400 million years. Plants host microorganisms that establish many different relationships with them, some negative and others very positive for both organisms. A type of this relationship is established with microorganisms that live inside them, known as endophytic microorganisms; they can include bacteria, yeasts, and fungi. In this study, we isolate endophytic bacteria from maize plants, and we characterize them in order to check their potential for being used as biocontrol agents against Botrytis cinerea, one of the most important phytopathogenic fungi in the world. The endophytic bacteria showed this antagonistic effect during in vitro assay and also during in vivo assay in Phaseolus vulgaris. At the same time, they showed the capacity for promoting growth in Zea mays plants.

Abstract

Plant diseases are one of the main factors responsible for food loss in the world, and 20–40% of such loss is caused by pathogenic infections. Botrytis cinerea is the most widely studied necrotrophic phytopathogenic fungus. It is responsible for incalculable economic losses due to the large number of host plants affected. Today, B. cinerea is controlled mainly by synthetic fungicides whose frequent application increases risk of resistance, thus making them unsustainable in terms of the environment and human health. In the search for new alternatives for the biocontrol of this pathogen, the use of endophytic microorganisms and their metabolites has gained momentum in recent years. In this work, we isolated endophytic bacteria from Zea mays cultivated in Colombia. Several strains of Bacillus subtilis, isolated and characterized in this work, exhibited growth inhibition against B. cinerea of more than 40% in in vitro cultures. These strains were characterized by studying several of their biochemical properties, such as production of lipopeptides, potassium solubilization, proteolytic and amylolytic capacity, production of siderophores, biofilm assays, and so on. We also analyzed: (i) its capacity to promote maize growth (Zea mays) in vivo, and (ii) its capacity to biocontrol B. cinerea during in vivo infection in plants (Phaseolus vulgaris).

Evaluation of bacillus megaterium strain AB4 as a potential biocontrol agent of alternaria japonica, a mycopathogen of Brassica oleracea var. italica

Alternaria japonica causes annual losses of up to 25 % of the world broccoli crops, for this reason this research focused on the development of biopreparations containing Bacillus megaterium to prevent the outbreak of this disease caused by Alternaria japonica in the crop of Brassica oleracea var. italica. During the laboratory phase two types of biopreparations were evaluated, the first biopreparation was obtained by liquid fermentation composed of 40 g.L^-1 of fava bean flour and 5 g.L^-1 of ground brown sugar. This showed a maximum cell growth of 3.8 × 10⁸ CFU. mL^-1; while the second biopreparation was obtained by solid fermentation composed of wheat bran and it achieved a maximum cell growth of 4.7 × 10⁹ CFU. g^-1. In the fieldwork phase the aforementioned biopreparations were applied in an open-field crop. At the end of the cultivation period, the degree of the disease in leaves and in the inflorescences was measured and through the statistical analysis, a significant difference was evidenced (α = 0.05). On the broccoli leaves the disease index values ​​do not exceed 15.56 % and the disease index for postharvest florets was around 38 %. The evaluated variables showed a statistical similarity with the chemical treatment, thus determining the effective effect of the biopreparations.

Antimicrobial activity and partial characterization of bacteriocin-like inhibitory substances produced by Lactobacillus spp. isolated from artisanal Mexican cheese

Lactobacillus spp. from Mexican Cocido cheese were shown to produce bacteriocin-like substances (BLS) active against Staphylococcus aureus,Listeria innocua,Escherichia coli, andSalmonella typhimurium by using the disk diffusion method. Crude extracts of Lactobacillus fermentum showed strong inhibitory activity against Staph. aureus, L. innocua, E. coli, and Salmonella cholerae. Complete inactivation of antimicrobial activity was observed after treatment of crude extracts with proteinase K, pronase, papain, trypsin, and lysozyme, confirming their proteinaceous nature. However, antimicrobial activity was partly lost for some of the crude extracts when treated with α-amylase, indicating that carbohydrate moieties were involved. The antimicrobial activity of the crude extracts was stable at 65°C for 30min over a wide pH range (2-8), and addition of potassium chloride, sodium citrate, ethanol, and butanol did not affect antibacterial activity. However, antimicrobial activity was lost after heating at 121°C for 15min, addition of methanol or Tween 80. Fourteen out of 18 Lactobacillus spp. showed antimicrobial activity against different test microorganisms, and 12 presented bacteriocin-like substances. Generation time and growth rate parameters indicated that the antimicrobial activity of crude extracts from 3 different strains was effective against the 4 indicator microorganisms. One of the crude extracts showed inhibition not only against gram-positive but also against gram-negative bacteria. Bacteriocin-like substances produced by this specific Lactobacillus strain showed potential for application as a food biopreservative.