Abdel Belarbi

Inhibitory effect of endophyte bacteria on Botrytis cinerea and its influence to promote the grapevine growth

Abstract A grapevine pathogen, Botrytis cinerea , produces characteristic gray mold symptoms on leaves and/or stems within 7 days following the inoculation. In this study we used a plant growth-promoting rhizobacterium, Pseudomonas sp. strain PsJN, which demonstrates an induction of plant growth in parallel with an antagonistic effect on in vitro growth and development of B. cinerea . The simultaneous in vitro co-culture of B. cinerea and bacterium did not stop the spread of fungus. However, when the fungus was introduced 2 days after bacterium inoculation, a clear inhibition of B. cinerea appeared around the zone of Pseudomonas inoculation. When in vitro bacterized plantlets were challenged with B. cinerea , the symptoms of gray mold failed to develop compared to nonbacterized controls. Microscopic observation of B. cinerea mycelium from the zone of contact between the fungus and with Pseudomonas sp. on the potato dextrose agar plate shows a growth disruption of fungal mycelium, coagulation, and leakage of protoplasm. The antagonist had no effect on the polygalacturonase activity of B. cinerea , meaning that the bacterium is not acting directly on the polygalacturonase of the fungus. It seems that the PsJN inhibits the growth of B. cinerea by disrupting cellular membranes and inducing cell death.

Thermophilic archaeal amylolytic enzymes

Abstract The discovery of thermophilic Archaea was one of the major scientific events of the last years, especially because their enzymes are of great interest. Effectively, these later concern numerous biotechnological applications such as the enzymatic starch-hydrolysis in glucose production. In this review, we examine the different thermophilic archaeal amylolytic enzymes already characterized, with particular attention to α-amylases, the most studied enzyme of the glycoside-hydrolase family. The ecological importance of these enzymes, as well as their biochemical properties, their structure, and their evolutionary relationships are described.

Genetic reidentification of the pectinolytic yeast strain SCPP as Saccharomyces bayanus var. uvarum

Abstract Using genetic hybridization analysis, pulsed-field gel electrophoresis of chromosomal DNA and PCR/RFLP analysis of the MET2 gene, we reidentified 11 Champagne yeast strains. Two of them, SCPP and SC4, were found to belong to Saccharomyces bayanus var. uvarum and the remaining strains to S. cerevisiae. Strain SCPP (CLIB 2025) of S. bayanus var. uvarum is known as a producer of three pectinolytic enzymes.

Interactions Between Yeasts and Grapevines: Filamentous Growth, Endopolygalacturonase and Phytopathogenicity of Colonizing Yeasts

It has been clearly established that phytopathogenic fungi, bacteria, and viruses exert biotic stresses on plants. Much less is known, however, about the interactions between enological species of yeast and their host plants. In a previous study, we described how Saccharomyces cerevisiae, the most common enological yeast, can act as a grapevine (Vitis vinifera L.) pathogen, causing growth retardation or plant death. In the present in vitro study on 11 strains of yeast belonging to different genera, which often occur on the surfaces of vineyard grapes and V. vinifera, a link was found to exist between strain phytopathogenecity and pseudohyphal growth habits and/or endopolygalacturonase activity. The results obtained here are consistent with earlier findings showing that the phytopathogenicity of yeast strains depends on the filamentous growth process, and show that endopolygalacturonase alone is not responsible for the invasion of plants tissues. The mechanisms observed here may be of significant ecological importance and may help to explain the long periods of yeast survival found to occur in vineyards.

Endopolygalacturonase of Saccharomyces cerevisiae: involvement in pseudohyphae development of haploids and in pathogenicity on Vitis vinifera

We have cloned the PGL1 gene from Saccharomyces cerevisiae, an poly-α-1,4 galacturonide glycanohydrolase (EC 3.2.1.15) commonly named endopolygalacturonase (endoPG), with a cis-acting regulatory region. This enzyme is known as pectin hydrolase, pectin being one of the main constituents of primary cell walls and middle lamella of higher plant cells. These pectins constitute a structural barrier to microbial invasion. The construct pRPGL1-2 has been introduced into the haploid receiver strain of S. cerevisiae, devoided of endoPG activity, to study the potential role of polygalacturonases in pathogenicity towards Vitis vinifera and in pseudohyphae formation. The latter corresponds to a switch from a single-cell form to the formation of long-branched chains of elongated cells, a phenomenon mainly reported for diploid yeast. We observed in the isogenic S. cerevisiae strains that endoPG, encoded by PGL1 gene, is required for pseudohyphae development and is involved in plant pathogenesis. The direct penetration of the host plant has been confirmed histologically for the transformed haploid receiver.

Use of a new gelling agent (Eladium©) as an alternative to agar-agar and its adaptation to screen biofilm-forming yeasts

The incidence of yeast-induced infections has increased in the last decade, mainly because of the increasing number of immunodeficient patients. Since biofilm production is believed to be responsible for fungal virulence, we propose screening yeasts of various genera in order to determine their ability to form biofilms. This is an important issue because yeast cells that form biofilms are particularly resistant to anti-fungal agents used in human patients. For screening, we used Eladium©, a new polysaccharide produced by a Rhizobium sp., as an alternative gelling agent to agar. We also established the conditions necessary to detect biofilm formation. The adapted medium provides the missing link between liquid and solid media. Its advantages include enhancement of growth of microorganisms and facilitation of quick and easy monitoring of biofilm formation.