Production and partial characterization of chitinase from a halotolerant Planococcus rifitoensis strain M2-26

peer reviewedThis paper is the first to investigate the production and partial characterization of the chitinase enzyme from a moderately halophilic bacterium Planococcus rifitoensis strain M2-26, earlier isolated from a shallow salt lake in Tunisia. The impact of salt, salinity concentration, pH, carbon and nitrogen sources on chitinase production and activity have been determined. This is the first report on a high salt-tolerant chitinase from P. rifitoensis, since it was active at high salinity (from 5 to 30% NaCl) as well as in the absence of salt. This enzyme showed optimal activity at 70 C and retained up to 82 and 66% of its original activity at 80 or 90 C, respectively. The activity of the enzyme was also shown over a wide pH range (from 5 to 11). For characterization of the enzyme activity, the chitinase secreted in the culture supernatant was partially purified. The preliminary study of the concentrated dialysed supernatant on native PAGE showed at least three chitinases produced by strain M2-26, with highest activity approximately at 65 kDa. Thus, the thermo-tolerant and high salt-tolerant chitinases produced by P. rifitoensis strain M2-26 could be useful for application in diverse areas such as biotechnology and agro-industry

Production and Characterization of New Biosurfactants/Bioemulsifiers from Pantoea alhagi and Their Antioxidant, Antimicrobial and Anti-Biofilm Potentiality Evaluations

The present work aimed to develop rapid approach monitoring using a simple selective method based on a positive hemolysis test, oil spreading activity and emulsification index determinations. It is the first to describe production of biosurfactants (BS) by the endophytic Pantoea alhagi species. Results indicated that the new BS evidenced an E24 emulsification index of 82%. Fourier-transform infrared (FTIR) results mentioned that the described BS belong to the glycolipid family. Fatty acid profiles showed the predominance of methyl 2-hyroxydodecanoate in the cell membrane (67.00%) and methyl 14-methylhexadecanoate (12.05%). The major fatty acid in the BS was oleic acid (76.26%), followed by methyl 12-methyltetradecanoate (10.93%). Markedly, the BS produced by the Pantoea alhagi species exhibited antimicrobial and anti-biofilm activities against tested human pathogens. With superior antibacterial activity against Escherchia coli and Staphylococcus aureus, a high antifungal effect was given against Fusarium sp. with a diameter of zone of inhibition of 29.5 mm, 36 mm and 31 mm, obtained by BS dissolved in methanol extract. The DPPH assay indicated that the BS (2 mg/mL) showed a higher antioxidant activity (78.07 inhibition percentage). The new BS exhibited specific characteristics, encouraging their use in various industrial applications

Biosynthesis and Characterization of Silver Nanoparticles from the Extremophile Plant Aeonium haworthii and Their Antioxidant, Antimicrobial and Anti-Diabetic Capacities

The present paper described the first green synthesis of silver nanoparticles (AgNPs) from the extremophile plant Aeonium haworthii. The characterization of the biosynthesized silver nanoparticles was carried out by using UV-Vis, FTIR and STM analysis. The antioxidant, antidiabetic and antimicrobial properties were also reported. The newly described AgNPs were spherical in shape and had a size of 35-55 nm. The lowest IC50 values measured by the DPPH assay indicate the superior antioxidant behavior of our AgNPs as opposed to ascorbic acid. The silver nanoparticles show high antidiabetic activity determined by the inhibitory effect of alpha amylase as compared to the standard Acarbose. Moreover, the AgNPs inhibit bacterial growth owing to a bactericidal effect with the MIC values varying from 0.017 to 1.7 mu g/mL. The antifungal action was evaluated against Candida albicans, Candida tropicalis, Candida glabrata, Candida sake and non-dermatophytic onychomycosis fungi. A strong inhibitory effect on Candida factors' virulence was observed as proteinase and phospholipase limitations. In addition, the microscopic observations show that the silver nanoparticles cause the eradication of blastospores and block filamentous morphogenesis. The combination of the antioxidant, antimicrobial and antidiabetic behaviors of the new biosynthesized silver nanoparticles highlights their promising use as natural phytomedicine agents

Biological control of Botrytis cinerea on stem wounds with moderately halophilic bacteria

International audienceInfection of tomato stem wounds by Botrytis cinerea is an important problem which can cause severe economic losses in greenhouse tomato crops. Three moderately halophilic bacteria were tested for their ability to protect pruning wounds from attacks by B. cinerea under growth chamber conditions. The severity of the disease estimated by the length of the rotted stem was used to calculate the area under the disease progress curves (AUDPC). Bacterial antagonists (B1, B2 and B3) were very effective in controlling Botrytis-infection on the tomato stems during the first 6 days and later by the end of the experiment. Plants treated with Bacillus subtilis (B1) had the lowest AUDPC (0). It was followed by B. subtilis (B3) and Halomonas sp. (B2) with AUDPC of 9.8 and 17.02, respectively. While the B1 strain best inhibited grey mold development when applied as young culture (24 h), the B3 strain performed better as an older culture (48 h). In contrast to the results obtained with Bacillus species, the efficacy of the bacterial treatment B2 seems to be independent of the growth phase. The co-cultures with fungal spores and either B. subtilis (B1) or Halomonas sp. (B2) applied as a 24 h bacterial culture completely inhibited the germination of B. cinerea after 24 h at 21_

High salt-tolerant protease from a potential biocontrol agent bacillus pumilus M3-16

In this paper, we investigate the characterization and evaluation of the antifungal protease activity from a halotolerant strain M3-16 of Bacillus pumilus, earlier isolated from a shallow salt lake in Tunisia. Protease enzyme was highly induced by the pathogen tested in vitro (27.4 U/ml). This is the first report on high salt-tolerant protease from B. pumilus, since it was active at high salinity (from 5 to 30% NaCl, w/v) as well as in the absence of salinity. This enzyme showed optimal activity at 60 °C and pH 8. At 80 °C and 30 min, the enzyme retained up to 91% and it showed stability over a wide pH range (from pH 5 to 11). The enzyme was found to be monomer with an estimated molecular mass of 31 kDa. The amino acid sequence showed high similarity (94%) to ATP-dependent protease from B. pumilus strain ATCC 7061. Thus, our alkaline thermostable and high salt-tolerant protease induced by a phytopathogenic fungus, could be useful for application in diverse areas such as biotechnology alimentary and agronomy industries

Characterization of a novel chitinase from a moderately halophilic bacterium, Virgibacillus marismortui strain M3-23

A new chitinase produced by the moderately halophilic bacterium Virgibacillus marismortui strain M3- 23 was identified and characterized. Distinguishable characteristics of high activity and stability at different pH, temperatures and salinity of M3-23 chitinase are reported. Analysis of the catalytic domain sequence from the enzyme highlighted its relationship to glycosyl hydrolase family 18. Comparison of the deduced chitinase sequence from strain M3-23 to known chitinases from Bacillus species showed low similarity (82%), suggested its novelty. This is the first report of the characterization of chitinase from the species V. marismortui. The halo- and thermo-tolerant nature of the chitinolytic enzyme allows its potential use in agricultural and industrial applications

Ability of moderately halophilic bacteria to control grey mould disease on tomato fruits

Tomato is one of the leading crops in Tunisia in terms of weight consumed (20 kg per person/year). Preserving the quality of the fruit from field to consumer is essential to successful marketing. Grey mould rot induced by Botrytis cinerea is an important cause of postharvest loss depending on season and handling practices. We describe here the ability of halotolerant to moderately halophilic bacteria isolated from different Tunisian Sebkhas (hypersaline soils) to protect freshmarket tomato fruits from B. cinerea. The tomatoes tested were at two different stages of ripening, (i) mature-green and (ii) red. Six strains significantly reduced growth of the pathogens from 67% to 87%. The effectiveness of these antagonists was also confirmed on green tomatoes; in which the fruit rot protection rate ranged from 74% to 100%. The antagonists were characterized by morphological, biochemical and physiological tests as well as 16S rDNA sequencing. The halotolerant effective isolates were identified as belonging to one of the species Bacillus subtilis (M1-20, J9) or B. licheniformis (J24). One effective moderately halophilic isolate (M2-26) was identified as Planococcus rifietoensis. These strains are a source of hydrolytic enzymes such as chitinases, proteases, laminarinases, amylases, lipases and cellulases. For comparison, 12 halotolerant or moderately halophilic strains obtained from DSM culture collection were also evaluated for their antifungal activity against B. cinerea on tomato fruits. The most effective strains were Halonionas subglaciescola, Halobacillus litoralis, Marinococcus halophilus, Salinococcus roseus, Halovibrio variabilis and Halobacillus halophilus with a percentage of grey mould rot reduction ranging from 71% to 97%. Inoculation of mature-green tomatoes by the bacterial antagonist of Halobacillus trueperi resulted in no disease development. Our results indicate that the use of halotolerant to halophilic microorganisms should be helpful in reducing grey mould disease of stored tomatoes

First Report of the Biosynthesis and Characterization of Silver Nanoparticles Using Scabiosa atropurpurea subsp. maritima Fruit Extracts and Their Antioxidant, Antimicrobial and Cytotoxic Properties

Candida and dermatophyte infections are difficult to treat due to increasing antifungal drugs resistance such as fluconazole, as well as the emergence of multi-resistance in clinical bacteria. Here, we first synthesized silver nanoparticles using aqueous fruit extracts from Scabiosa atropurpurea subsp. maritima (L.). The characterization of the AgNPs by means of UV, XRD, FTIR, and TEM showed that the AgNPs had a uniform spherical shape with average sizes of 40–50 nm. The biosynthesized AgNPs showed high antioxidant activity when investigated using 1, 1-diphenyl-2- picryl-hydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) assays. The AgNPs displayed strong antibacterial potential expressed by the maximum zone inhibition and the lowest MIC and MBC values. The AgNPs revealed a significant antifungal effect against the growth and biofilmof Candida species. In fact, the AgNPs were efficient against Trichophyton rubrum, Trichophyton interdigitale, and Microsporum canis. The antifungal mechanisms of action of the AgNPs seem to be due to the disruption of membrane integrity and a reduction in virulence factors (biofilm and hyphae formation and a reduction in germination). Finally, the silver nanoparticles also showed important cytotoxic activity against the human multiple myeloma U266 cell line and the human breast cancer cell line MDA-MB- 231. Therefore, we describe new silver nanoparticles with promising biomedical application in the development of novel antimicrobial and anticancer agents