Heavy metal tolerant Pseudomonas protegens isolates from agricultural well water in northeastern Algeria with plant growth promoting, insecticidal and antifungal activities

The application of plant growth promoting bacteria (PGPB) with biocontrol activities as inoculants of crop plants against phytopathogenic fungi and insect pests provide a biological alternative to the use of agrochemicals. Two Pseudomonas protegens strains were isolated from agricultural well water in a heavy metal contaminated area near Bejaia, northeastern Algeria. The isolates S4LiBe and S5LiBe had 16S rRNA gene sequence similarities of 99.4%–99.7% with P. protegens CHA0T and other P. protegens strains. The phenotypic profiles tested with BIOLOG-GN2-microplates showed differences in 12 of 95 carbon sources tested, as compared to the type strain P. protegens CHA0T. The isolates S4LiBe and S5LiBe showed plant growth promoting potential which is commonly associated with the production of the phytohormone indole acetic acid and siderophores and the solubilization of insoluble phosphate. In addition, they produce chitinase and other polymer degrading enzymes. As the strains S4LiBe and S5LiBe were isolated from heavy metal polluted well water, they are resistant against several heavy metals (2.0 mM K2Cr2O7 and 3.0 mM CoSO4, HgSO4, CdSO4 8H2O and PbCl2), while the reference strain P. protegens CHA0T was very sensitive to Hg2+ and Cd2+ and had lower tolerance towards Co2+ and Pb2+. The isolates S4LiBe and S5LiBe were active in mycelial growth inhibition assays against Botrytis cinerea, Verticillium dahliae, Fusarium graminearum, Aspergillus niger and Aspergillus flavus (growth inhibition between 88% and 48%). Furthermore, S4LiBe and S5LiBe showed effective insecticidal activities, when tested in the Galleria injection assay and they were tested positive for the insect toxin gene fitD alike the reference strain CHA0T. Finally, inoculation of barley seeds with S5LiBe in non-polluted agricultural soil significantly stimulated the germination rate and growth of seedlings, with increased shoot length (11.96 cm ± 0.59), shoot and root fresh weight (0.10 g ± 0.009, 0.04 g ± 0.006), shoot and root dry weight (0.075 g ± 0.003, 0.03 g ± 0.007) as compared to non-inoculated plants (10.23 cm ± 0.84, 0.06 g ± 0.007, 0.025 g ± 0.006, 0.047 g ± 0.006, and 0.016 g ± 0.004, respectively). In heavy metal contaminated soil, inoculation with strain S5LiBe resulted in similar increase of germination rate and growth parameters of barley like in the non-polluted soil, while P. protegens CHA0T inoculated plants were not stimulated. Thus, the heavy metal tolerant isolates S4LiBe and S5LiBe have a potential as beneficial bacteria for agricultural application even in heavy metal polluted soils, e.g. for the stimulation of biomass crops. The demonstration of successful isolation from agricultural well water may open more ready access for a wide variety of this kind of beneficial bacteria for agricultural application

Application of halotolerant bacteria to restore plant growth under salt stress.

High salinity abolishes several stages of plant life ranging from the seed germination step to maturity. Many processes are inhibited, such as phytohormone synthesis and regulation, normal root and shoot development, nutrient uptake, photosynthesis, and DNA replication. Plant growth promoting bacteria (PGPB) are naturally colonizing plants and occur in the rhizosphere or non rhizosphere soil and benefit plant growth by numerous processes. The importance of halotolerant PGPB resides in their ability to adapt to increased salinity by efficient osmoregulatory mechanism to be able to continue regular cell functions. Thus, halotolerant PGPB are able to provide plants with their activities to challenge osmotic stress by supporting them in the restoration of essential activities, e.g., in their hormonal balance. Halotolerant PGPB stimulate plant growth under high salinity by using similar mechanisms like halosensitive PGPB, such as synthesis of indole acetic acid (IAA), gibberellins (GA), cytokinins (CK), abscisic acid (ABA), solubilization of insoluble phosphate, synthesis and excretion of siderophores, and production of ACCdeaminase to reduce high growth inhibitory levels of ethylene occurring in plants at salt stress conditions. Furthermore, some halotolerant PGPB are even able to colonize plants endophytically, produce various antimicrobial metabolites against pathogenic fungi and bacteria, support plant health by improving systemic resistance and contribute to soil fertility and remediation

Impact of seaweeds on agricultural crop production as biofertilizer.

Seaweeds or marine macroalgae are rich in diverse compounds like lipids, proteins, carbohydrates, phytohormones, amino acids, osmoprotectants, antimicrobial compounds and minerals. Their potential for agricultural applications is used since antiquity, but recent demands of organic farming and organic food stimulated much the application of organic treatments like seaweed extracts in agriculture. The benefits of seaweeds application in agricultural field are numerous and diverse such as stimulation of seed germination, enhancement of health and growth of plants namely shoot and root elongation, improved water and nutrient uptake, frost and saline resistance, biocontrol and resistance toward phytopathogenic organisms, remediation of pollutants of contaminated soil and fertilization. In this review, scientific progress in this field was collected and critically assessed to lay grounds for further investigations and applications

A halophilic and osmotolerant Azospirillum brasilense strain from Algerian soil restores wheat growth under saline conditions

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A halophilic and osmotolerant Azospirillum brasilense strain from Algerian soil restores wheat growth under saline conditions.

A new bacterial isolate (NH) from salt-affected soil was identified as Azospirillum brasilense using phenotypic analyses and 16SrDNA-based phylogeny. This isolate showed resistance towards 3,4-dehydroproline and optimal growth at 200 mmol/L NaCl, tolerating salt stress of 300 mmol/L NaCl in the absence of osmoprotectants and up to 600 mmol/L NaCl in the presence of glycine betaine and Ova lactuca extracts. This effect was enhanced with extracts of the marine algae Ova lactuca. A. brasilense strain NH can produce auxin indole acetic acid under saline conditions. The hypothesis was tested that the inoculation of this osmotolerant rhizosphere strain could improve the growth of wheat under saline stress conditions. Normal wheat growth was restored in the presence of both 150 mmol/L and 200 mmol/L NaCl after inoculation with A. brasilense NH. Under saline conditions, its effect of promoting plant growth of wheat was significantly superior to that of A. brasilense Sp7, the non-halotolerant type strain. A. brasilense NH restored wheat growth at elevated salt concentrations in pot and field experiments even better in the presence of osmoprotective Ulva lactuca extracts

Restoration of growth of durum wheat (Triticum durum var. waha) under saline conditions due to inoculation with the rhizosphere bacterium Azospirillum brasilense NH and extracts of the marine alga Ulva lactuca.

Inoculation with the rhizosphere bacterium Azospirillum brasilense NH, originally isolated from salt-affected soil in northern Algeria, greatly enhanced growth of durum wheat (Triticum durum var. waha) under saline soil conditions. Important plant parameters like the rate of germination, stem height, spike length, dry weight of roots and shoots, chlorophyll a and b content, proline and total sugar contents, 1000-seed weight, seed number per spike, and weight of seeds per spike were measured. At salt stress conditions (160 and 200 mM NaCl) A. brasilense NH restored almost completely vegetative growth and seed production. The combination with extracts of the marine alga Ulva lactuca resulted in even more improved salt tolerance of durum wheat. Proline and total sugar accumulation, a sign of physiological plant stress under inhibitory salt conditions, was reduced in plants inoculated with A. brasilense NH with and without addition of algal extracts. Inoculation with the salt-sensitive A. brasilense strain Sp7 could not restore salt-affected plant growth at 200 mM NaCl. Furthermore, it could be demonstrated by fluorescence in situ hybridization and confocal laser scanning microscopy that A. brasilense NH is able to colonize roots of durum wheat endophytically under salt-stressed conditions. Thus, the salt-tolerant rhizobacterium A. brasilense NH could effectively provide alone or in combination with extracts of U. lactuca a promising solution to overcome salt inhibition which is a major threat hindering productive wheat cultivation in arid saline soils

Growth stimulation of barley and biocontrol effect on plant pathogenic fungi by a <em>Cellulosimicrobium</em> sp. strain isolated from salt-affected rhizosphere soil in northwestern Algeria.

The plant growth promoting effect of bacterial isolates from salt-affected agricultural rhizospheric soil from Bejaia, Algeria, on barley seedlings as well as biological control abilities of these isolates against phytopathogenic fungi were determined. Four isolates stimulated significantly germination and growth of barley seedlings in an axenic test system and in soil pots. Isolate S16 (Cellulosimicrobium sp.) stimulated the growth of barley seedlings by 185% (stem height of 13.0&plusmn;0.11cm) over non-inoculated control seedlings (7.0&plusmn;0.12cm). Cellulosimicrobium sp. S16 was found also superior in mycelial growth inhibition assays against the plant pathogenic fungi Botrytis cinerea, Fusarium oxysporum and Verticillium dahliae. Furthermore, several plant growth promoting traits (production of indole acetic acid, inorganic phosphate solubilization, siderophore production) and production of enzymes beneficial for soil fertility (protease, chitinase, amylase and urease) were identified. However, no evidence for nitrogen fixation was found by testing acetylene reduction and the presence of nif-genes. Based on comparative sequence analysis of almost full length 16S-rRNA coding gene fragments, Cellulosimicrobium sp. S16 exhibits the highest similarity of 99.7% to Cellulosimicrobium cellulans (accession number AY665978). Cellulosimicrobium sp. S16 could be a successful candidate for the application as a plant growth promoting inoculant