Bioprospecting of Plant Growth Promoting Bacilli and Related Genera Prevalent in Soils of Pristine Sacred Groves: Biochemical and Molecular Approach

Biochemical, Catabolic, and PGP Activity of Microbial Communities and Bacterial Strains from the Root Zone of Baccharis linearis in a Mediterranean Mine Tailing

The management of mine tailings (MT) is commonly workload heavy, intrusive, and expensive. Phytostabilization offers a promising approach for MT management; however, it poses challenges due to the unfavorable physicochemical properties of these wastes. Nevertheless, native microorganisms capable of supporting plant growth and development could enhance the efficacy of phytostabilization. This study assesses the biological activity of microbial communities from the root zone of Baccharis linearis, which is naturally present in MT, in order to evaluate their biotechnological potential for phytostabilization. The root zone and bulk samples were collected from B. linearis plants located within a MT in the Mediterranean zone of Chile. Enzyme activities related to the cycling of C, N, and P were assessed. The community-level physiological profile was evaluated using the MicroRespTM system. Bacterial plant growth-promoting (PGP) traits and colony forming units (CFU) were evaluated through qualitative and microbiological methods, respectively. CFU, enzyme activities, and CLPP were higher in the root zone compared with the bulk samples. Five bacterial strains from the root zone exhibited PGP traits such as P solubilization and N acquisition, among others. The presence of microbial communities in the root zone of B. linearis with PGP traits suggests their potential to enhance the ecological management of MT through phytostabilization programs.

In vitro Screening of Sunflower Associated Endophytic Bacteria With Plant Growth-Promoting Traits

Harnessing endophytic microbes as bioinoculants promises to solve agricultural problems and improve crop yield. Out of fifty endophytic bacteria of sunflowers, 20 were selected based on plant growth-promoting. These plant growth-promoting bacteria were identified as Bacillus, Pseudomonas, and Stenotrophomonas. The qualitative screening showed bacterial ability to produce hydrogen cyanide, ammonia, siderophore, indole-3-acetic acid (IAA), exopolysaccharide, and solubilize phosphate. The high quantity of siderophore produced by B. cereus T4S was 87.73%. No significant difference was observed in the Bacillus sp. CAL14 (33.83%), S. indicatrix BOVIS40 (32.81%), S. maltophilia JVB5 (32.20%), S. maltophilia PK60 (33.48%), B. subtilis VS52 (33.43%), and P. saponiphilia J4R (33.24%), exhibiting high phosphate-solubilizing potential. S. indicatrix BOVIS40, B. thuringiensis SFL02, B. cereus SFR35, B. cereus BLBS20, and B. albus TSN29 showed high potential for the screened enzymes. Varied IAA production was recorded under optimized conditions. The medium amended with yeast extract yielded high IAA production of 46.43 μg/ml by S. indicatrix BOVIS40. Optimum IAA production of 23.36 and 20.72 μg/ml at 5% sucrose and 3% glucose by S. maltophilia JVB5 and B. cereus T4S were recorded. At pH 7, maximum IAA production of 25.36 μg/ml was obtained by S. indicatrix BOVIS40. All the isolates exhibited high IAA production at temperatures 25, 30, and 37°C. The in vitro seed inoculation enhanced sunflower seedlings compared to the control. Therefore, exploration of copious endophytic bacteria as bioinoculants can best be promising to boost sunflower cultivation.

Tobacco Plant Growth-Promoting and Antifungal Activities of Three Endophytic Yeast Strains

In this research, the biosynthetic and biocontrol potential of endophytic yeast to improve the growth and development of tobacco has been elucidated. Three yeast strains were enriched and isolated from different plant tissues. Partial sequence analysis of ITS5-5.8-ITS4 region of the nuclear ribosomal DNA with universal primers identified YD5, YE1, and YSW1 as Saccharomyces cerevisiae (S. cerevisiae), Zygosaccharomyces bailii (Z. bailii), and Saccharomyces kudriavzevii (S. kudriavzevii), respectively. When cultivated in a medium supplemented with 0.1% L-tryptophan, isolated yeast strains produced indole-3-acetic acid (IAA). The capacities of those strains to improve the mobility of phosphorus and synthesize siderophores has been proven. Their antimicrobial activities against several Solanaceae plant pathogenic fungi (Alternaria solani pathovar. tobacco, Rhizoctonia solani, and Fusarium solani pathovar. phaseoli) were determined. S. cerevisiae YD5, Z. bailii YE1, and S. kudriavzevii YSW1 inhibited the growth of all tested pathogens. Yeast strains were tested for endophytic colonization of tobacco by two different inoculation methods: soil drench (SD) and leaf spraying (LS). To establish colonization in the various tissues of tested tobacco (Nicotiana tabaccum L.) plants, samples were taken on the seventh, fourteenth, and twenty-first days after treatment (DAT), and explants were inoculated on yeast malt agar (YMA). Both techniques of inoculation showed a high frequency of colonization from 83.33% to 100%. To determine the effectiveness of the microbial endophytes, their effect on some physiological processes in the plant were analyzed, such as photosynthesis, stomatal conductivity, and transpiration intensity. The effect of single and double treatment with yeast inoculum on the development and biochemical parameters of tobacco was reported. Plants have the ability of structural and functional adaptation to stress effects of different natures. All treated plants had a higher content of photosynthetic pigments compared to the control. Photosynthesis is probably more intense, and growth stimulation has been observed. The chlorophyll a/b ratio remained similar, and the total chlorophyll/carotenoid ratio slightly increased as a result of elevated chlorophyll levels. The most significant stimulating effect was recorded in tobacco plants treated by foliar spraying with Z. bailii YE1 and S. cerevisiae YD5. In contrast, S. kudriavzevii YSW1 had a better effect when applied as a soil drench. Thus, S. cerevisiae YD5, Z. bailii YE1, and S. kudriavzevii YSW1 have a high potential to be used as a biocontrol agents in organic agriculture.

Rhizobacteria from 'flowering desert' events contribute to the mitigation of water scarcity stress during tomato seedling germination and growth

Tomato (Solanum lycopersicum L.) is an important vegetable cultivated around the world. Under field conditions, tomato can be negatively affected by water scarcity in arid and semiarid regions. The application of native plant growth-promoting rhizobacteria (PGPR) isolated from arid environments has been proposed as an inoculant to mitigate abiotic stresses in plants. In this study, we evaluated rhizobacteria from Cistanthe longiscapa (syn Calandrinia litoralis and Calandrinia longiscapa), a representative native plant of flowering desert (FD) events (Atacama Desert, Chile), to determine their ability to reduce water scarcity stress on tomato seedlings. The isolated bacterial strains were characterized with respect to their PGPR traits, including P solubilization, 1-aminocyclopropane-1-carboxylate deaminase activity, and tryptophan-induced auxin and exopolysaccharide production. Three PGPR consortia were formulated with isolated Bacillus strains and then applied to tomato seeds, and then, the seedlings were exposed to different levels of water limitations. In general, tomato seeds and seedlings inoculated with the PGPR consortia presented significantly (P ≤ 0.05) greater plant growth (48 to 60 cm of height and 171 to 214 g of weight) and recovery rates (88 to 100%) compared with those without inoculation (37 to 51 cm of height; 146 to 197 g of fresh weight; 54 to 92% of recovery) after exposure to a lack of irrigation over different time intervals (24, 72 and 120 h) before transplantation. Our results revealed the effectiveness of the formulated PGPR consortia from FD to improve the performance of inoculated seeds and seedlings subjected to water scarcity; thus, the use of these consortia can represent an alternative approach for farmers facing drought events and water scarcity associated with climate change in semiarid and arid regions worldwide.

Comparative assessment of multi-trait plant growth-promoting endophytes associated with cultivated and wild Oryza germplasm of Assam, India

This paper presents a comparative study of endophytic bacteria from cultivated (Oryza sativa) and wild rice (Oryza rufipogon) plants and their functional traits related to plant growth promotion. A total of 70 bacterial isolates were characterized by both biochemical and molecular identification methods. Taxonomic classification showed dominance of three major phyla, viz, Firmicutes (57.1%), Actinobacteria (20.0%) and Proteobacteria (22.8%). Screening for in vitro plant growth-promoting activities revealed a hitherto unreported endophytic bacterium from wild rice germplasm, Microbacterium laevaniformans RS0111 with highest indole acetic acid (28.39 ± 1.39 µg/ml) and gibberellic acid (67.23 ± 1.83 µg/ml) producing efficiency. Few other endophytic isolates from cultivated rice germplasm such as Bacillus tequilensis RHS01 showed highest phosphate solubilizing activity (81.70 ± 1.98 µg/ml), while Microbacterium testaceum MKLS01 and Microbacterium enclense MI03 L05 showed highest potassium (53.42 ± 0.75 µg/ml) and zinc solubilizing activity (157.50%). Fictibacillus aquaticus LP20 05 produced highest siderophore (64.8%). In vivo evaluation of plant growth-promoting efficiencies of the isolates showed that Microbacterium laevaniformans RS0111, Microbacterium testaceum MKLS01 and Bacillus tequilensis RHS 01 could increase rice grain yield by 3.4-fold when compared to the control group. This study indicates the potentiality of rice endophytes isolates as an effective bioinoculants.

Multifunctional potential of endophytic bacteria from Anacardium othonianum Rizzini in promoting in vitro and ex vitro plant growth

Anacardium othonianum Rizzini, a cashew tree native to the Brazilian Cerrado, is economically important due to its applications in the food, chemical and pharmaceutical industries. However, A. othonianum yields a crop with low productivity due to a number of factors, such as nutritionally poor soils, drought and losses due to pests and diseases. Brazil is one of the nine largest cashew nut producers worldwide, and sustainable technologies are needed to increase the productivity of this crop. In this context, the use of endophytic microorganisms could promote plant growth and provide protection against phytopathogens. In this study, the isolation of the root endophytic community of A. othonianum led to the characterization of 22 distinct bacterial strains with multifunctional traits for plant growth promotion. The results of in vitro assays to assess auxin synthesis, phosphate solubilization, phosphatase and siderophore production and biocontrol against Fusarium oxysporum led to the selection of Acinetobacter lwoffii Bac109 and Pantoea agglomerans Bac131 as the most promising strains. The reinoculation of the Bac109 and Bac131 strains onto A. othonianum seeds showed that the treatment containing a mixture of these strains was the most effective in promoting increases in the biometric parameters of early plant growth. Thus, this study highlights the biotechnological potential of a consortium of A. lwoffii Bac109 and P. agglomerans Bac131 for future applications in sustainable cashew cultivation.

Functional and molecular characterization of plant growth promoting Bacillus isolates from tomato rhizosphere

The rhizosphere offers a quintessential habitat for the microbial communities and facilitates a variety of plant-microbe interactions. Members of the genus Bacillus constitute an important group of plant growth promoting rhizobacteria (PGPR), which improve growth and yield of crops. In a total of 60 bacterial isolates from the tomato rhizosphere, 7 isolates were selected based on distinct morphological characteristics and designated as tomato rhizosphere (TRS) isolates with a number suffixed viz., TRS-1, 2, 3, 4, 5, 7, and TRS-8. All the seven isolates were Gram positive, with in vitro plant growth promoting (PGP) traits like phosphate and zinc solubilization, and also produced indoleacetic acid (IAA), phytase, siderophore, hydrogen cyanide (HCN), and 1-aminocyclopropane-1-carboxylate (ACC) deaminase, besides being antagonistic to other microbes and formed biofilm. The seven isolates belonged to the genus Bacillus as per the 16S rDNA sequence analysis. Phylogenetic tree grouped the isolates into four groups, while BOX-PCR fingerprinting allowed further differentiation of the seven isolates. The PGP activity of the isolates was measured on tomato seedlings in plant tissue culture and greenhouse assays. A significant increase in root colonization was observed over 15 days with all the isolates. Greenhouse experiments with these isolates indicated an overall increase in the growth of tomato plants, over 60 days. Isolates TRS-7 and TRS-8 were best plant growth promoters among the seven isolates, with a potential as inoculants to increase tomato productivity.

Dry-Caribbean Bacillus spp. Strains Ameliorate Drought Stress in Maize by a Strain-Specific Antioxidant Response Modulation

Drought is a global problem for crop productivity. Therefore, the objective of this research was to evaluate five dry-Caribbean Bacillus spp. strains in drought stress amelioration in maize plants. Maize seeds were single-strain inoculated and sown in pots under greenhouse conditions. After 12 days, plants were subjected to 33 days of drought conditions, i.e., 30% of soil field capacity, and then collected to measure leaf and root dry biomass, plant height, antioxidant enzymes, proline accumulation, and P⁺, Ca²⁺, and K⁺ uptake. Results correlated drought stress amelioration with the inoculation of Bacillus spp. strains XT13, XT38 and XT110. Inoculated plants showed increases in dry biomass, plant height, and K⁺ and P⁺ uptake. The overall maize antioxidant response to bacterial inoculation under drought stress showed dependence on proline accumulation and decreases in ascorbate peroxidase and glutathione reductase activities. Moreover, results suggest that this stress amelioration is driven by a specific plant-strain correlation observed in antioxidant response changes in inoculated plants under stress. Also, there is a complex integration of several mechanisms, including plant growth-promotion traits and nutrient uptake. Hence, the use of dry-Caribbean plant growth-promoting Bacillus strains represents an important biotechnological approach to enhance crop productivity in arid and semi-arid environments.

Multiple Plant Growth-Promotion Traits in Endophytic Bacteria Retrieved in the Vegetative Stage From Passionflower

Bacteria exhibiting beneficial traits like increasing the bioavailability of essential nutrients and modulating hormone levels in plants are known as plant growth promoting (PGP) bacteria. The occurrence of this specific group of bacteria in the endophytic environment may reflect the decisive role they play in a particular condition. This study aimed to determine the taxonomical diversity of the culturable bacterial endophytes, isolated in the vegetative stage of passionflower (Passiflora incarnata), and assess its potential to promote plant growth by phenotypic and genotypic approaches. The sequencing and phylogenetic analysis of the 16S rRNA gene allowed us to classify 58 bacterial endophytes into nine genera. Bacillus (70.7%) was the most dominant genus, followed by Pseudomonas (8.6%) and Pantoea (6.9%). A few isolates belonged to Rhodococcus and Paenibacillus, whereas the genera Lysinibacillus, Microvirga, Xanthomonas, and Leclercia were represented by only one isolate. The strains were tested for nitrogen fixation, phosphate solubilization, indole-acetic-acid synthesis, and siderophore production. Moreover, PGP related genes (nifH, ipdC, asb, and AcPho) were detected by PCR-based screening. Most of the isolates (94.8%) displayed a potential for at least one of the PGP traits tested by biochemical assays or PCR-based screening. Nine strains were selected based on results from both approaches and were evaluated for boosting the Cape gooseberry (Physalis peruviana) germination and growth. All tested isolates improved germination in vitro, and the majority (78%) increased growth parameters in vivo. The results suggested that most of culturable bacteria inhabiting P. incarnata in the vegetative stage could be used as probiotics for agricultural systems. Besides, their occurrence may be associated with specific physiological needs typical of this development stage.

Bacillus Methylotrophicus Has Potential Applications Against Monilinia Fructicola

Biocontrol is a cost-effective and environmentally friendly technique used in agricultural production. We isolated and screened a bacterial strain from the soils of a peach orchard with high yield. Using biochemical and physiological analysis as well as phylogenetic sequencing data, we identified a strain of Bacillus methylotrophicus, strain XJ-C. The results of our screening trials showed that XJ-C was able to suppress M. fructicola at an inhibition rate of 81.57%. Following the application of a 1×10⁹ CFU/mL XJ-C strain suspension to the fruits, leaves, and shoots of peach trees infected with M. fructicola, the inhibition rate reached 64.31%, 97.34%, and 64.28%, respectively. Using OM and SEM, we observed that, under the inhibition of strain XJ-C, M. fructicola mycelium and spores were abnormally shaped. Under TEM, cell walls were transparent, organelles had disappeared, and the intracellular vacuole was deformed. Thus, XJ-C has the potential to be used in biocontrol.

Bacillus thuringiensis as a Biofertilizer and Biostimulator: a Mini-Review of the Little-Known Plant Growth-Promoting Properties of Bt

Bacillus thuringiensis (Bt) is a gram-positive spore-forming soil microorganism. Because the insecticidal activities of Bt are well known, it has been used as a tool for insect pest control worldwide. The beneficial features of Bt are not limited to its role as an insecticide; it is also used to control phytopathogenic fungi via chitinolytic activity. Bt-related studies are mostly focused on its biocontrol properties. However, studies focusing on the biostimulation and biofertilizer features of Bt, including its interactions with plants, are limited. Bt is a successful endophyte in many plants and can directly promote their development or indirectly induce plant growth by suppressing diseases. Although there are various commercial biopesticide Bt-based products, there are no commercial Bt-based plant growth-promoting rhizobacteria products on the biofertilizer market. As novel Bt strain exploration increases, there will likely be new Bt-based products with powerful biofertilizer activities in the future. The objective of this paper is to review, discuss, and evaluate the exceptional features of Bt as a plant growth promoter.

Bactéries sporulées et biofilms : un problème récurrent dans les lignes de production de lait reconstitué ou recombiné pasteurisé

In the dairy industry, bacterial contaminants persist on equipment surfaces due to spore and biofilm formation. These are involved in cross-contamination problems that affect the quality of processed products and limit their life. The pasteurization process, in which milk is submitted to moderate heat treatment, is inefficient against bacterial spores. The most prevalent sporulated bacteria belong to Bacillus and related genera. The situation is more complicated in countries where pasteurized milk is derived from imported milk powder originally contaminated by bacterial spores. Studies have shown biofilm formation on dairy equipment by mesophilic strains from the group Bacillus cereus and thermophilic strains from the genus Geobacillus. These biofilms are resistant to cleaning procedures and are sources of chronic contamination of pasteurized milk. This review analyzes the dairy situation in Algeria exposed to sporulated flora and derived biofilm problems, with the aim of proposing efficient solutions in the light of current knowledge. [Journal translation].

Heavy metal mediated phytotoxic impact on winter wheat: oxidative stress and microbial management of toxicity by Bacillus subtilis BM2

Heavy metals are toxic environmental contaminants, which severely affect microbial composition and functions and, concurrently, crop production. Due to these issues, the present study focussed on the selection of metal tolerant microbes endowed with metal detoxification abilities and their role in the management and remediation of metal contaminated soils. The metal tolerant bacterium BM2, identified as Bacillus subtilis by 16SrRNA gene sequencing, survived well under metal pressure and tolerated 1600 and 2000 μg mL-1 of Ni and Pb, respectively. The inhibitory impact of metals on wheat increased consistently with a progressive increase in metal concentration. Deposition of Ni and Pb within root and leaf and oxidative stress were validated by SEM, EDX and CLSM. The overall growth parameters of wheat grown under metal stress were improved following B. subtilis BM2 colonization. As an example, B. subtilis with 195 mg Pb kg-1 enhanced the length and dry biomass of shoots by 14% and 23%, respectively, over the control. Also, strain BM2 improved the grain yield significantly by 49% at 870 mg Ni kg-1 and by 50% at 585 mg Pb kg-1 compared to uninoculated plants. Moreover, B. subtilis BM2 relieved the metal stress on wheat and caused a significant drop in proline and malondialdehyde content and the activities of antioxidant enzymes, like catalase (CAT), superoxide dismutase (SOD) and glutathione reductase (GR). This study, therefore, provided solutions to the metal toxicity problems faced by winter wheat and clearly suggests that the metal detoxification potential of B. subtilis BM2 could be greatly useful in the management of metal polluted soils.

Exploring plant-microbe interactions of the rhizobacteria Bacillus subtilis and Bacillus mycoides by use of the CRISPR-Cas9 system

Bacillus subtilis HS3 and Bacillus mycoides EC18 are two rhizosphere-associated bacteria with plant growth-promoting activity. The CRISPR-Cas9 system was implemented to study various aspects of plant-microbe interaction mechanisms of these two environmental isolates. The results show that fengycin and surfactin are involved in the antifungal activity of B. subtilis HS3. Moreover, this strain emits several other volatile organic compounds than 2,3-butanediol, contributing to plant growth promotion. Confocal laser scanning microscopy observations of the GFP-labelled strain showed that HS3 selectively colonizes root hairs of grass (Lolium perenne) in a hydroponic system. For B. mycoides EC18, we found that the wild-type EC18 strain and a ΔasbA (petropectin-deficient) mutant, but not the ΔdhbB (bacillibactin-deficient) and ADKO (asbA and dhbB double knockout) mutants, can increase the plant biomass and total chlorophyll. All the mutant strains have a reduced colonization capability on Chinese cabbage (Brassica rapa) roots, at the root tip and root hair region compared with the wild-type strain. These results indicate that the siderophore, bacillibactin, is involved in the plant growth promoting activity and could affect the root colonization of B. mycoides. Collectively, the CRISPR-Cas9 system we developed for environmental isolates is broadly applicable and will facilitate deciphering the mechanisms of Bacillus-plant interactions. © 2018 The Authors.