Multifarious beneficial traits and plant growth promoting potential of Serratia marcescens KiSII and Enterobacter sp. RNF 267 isolated from the rhizosphere of coconut palms (Cocos nucifera L.)

Enhancing spinach (Spinacia oleracea L.) resilience in pesticide-contaminated soil: Role of pesticide-tolerant Ciceribacter azotifigens and Serratia marcescens in root architecture, leaf gas exchange attributes and antioxidant response restoration

This study unveils the detoxification potential of insecticide-tolerant plant beneficial bacteria (PBB), i.e., Ciceribacter azotifigens SF1 and Serratia marcescens SRB1, in spinach treated with fipronil (FIP), profenofos (PF) and chlorantraniliprole (CLP) insecticides. Increasing insecticide doses (25-400 μg kg-1 soil) significantly curtailed germination attributes and growth of spinach cultivated at both bench-scale and in greenhouse experiments. Profenofos at 400 μg kg-1 exhibited maximum inhibitory effects and reduced germination by 55%; root and shoot length by 78% and 81%, respectively; dry matter accumulation in roots and shoots by 79% and 62%, respectively; leaf number by 87% and leaf area by 56%. Insecticide application caused morphological distortion in root tips/surfaces, increased levels of oxidative stress, and cell death in spinach. Application of insecticide-tolerant SF1 and SRB1 strains relieved insecticide pressure resulting in overall improvement in growth and physiology of spinach grown under insecticide stress. Ciceribacter azotifigens improved germination rate (10%); root biomass (53%); shoot biomass (25%); leaf area (10%); Chl-a (45%), Chl-b (36%) and carotenoid (48%) contents of spinach at 25 μg CLP kg-1 soil. PBB inoculation reinvigorated the stressed spinach and modulated the synthesis of phytochemicals, proline, malondialdehyde (MDA), superoxide anions (O2•-), and hydrogen peroxide (H2O2). Scanning electron microscopy (SEM) revealed recovery in root tip morphology and stomatal openings on abaxial leaf surfaces of PBB-inoculated spinach grown with insecticides. Ciceribacter azotifigens inoculation significantly increased intrinsic water use efficiency, transpiration rate, vapor pressure deficit, intracellular CO2 concentration, photosynthetic rate, and stomatal conductance in spinach exposed to 25 μg FIP kg-1. Also, C. azotifigens and S. marcescens modulated the antioxidant defense systems of insecticide-treated spinach. Bacterial strains were strongly colonized to root surfaces of insecticide-stressed spinach seedlings as revealed under SEM. The identification of insecticide-tolerant PBBs such as C. azotifigens and S. marcescens hold the potential for alleviating abiotic stress to spinach, thereby fostering enhanced and safe production within polluted agroecosystems.

A novel strategy of artificially regulating plant rhizosphere microbial community to promote plant tolerance to cold stress

Artificial regulation of plant rhizosphere microbial communities through the synthesis of microbial communities is one of the effective ways to improve plant stress resistance. However, the process of synthesizing stress resistant microbial communities with excellent performance is complex, time-consuming, and costly. To address this issue, we proposed a novel strategy for preparing functional microbial communities. We isolated a cultivable cold tolerant bacterial community (PRCBC) from the rhizosphere of peas, and studied its effectiveness in assisting rice to resist stress. The results indicate that PRCBC can not only improve the ability of rice to resist cold stress, but also promote the increase of rice yield after cold stress relieved. This is partly because PRCBC increases the nitrogen content in the rhizosphere soil, and promotes rice's absorption of nitrogen elements, thereby promoting rice growth and enhancing its ability to resist osmotic stress. More importantly, the application of PRCBC drives the succession of rice rhizosphere microbial communities, and promotes the succession of rice rhizosphere microbial communities towards stress resistance. Surprisingly, PRCBC drives the succession of rice rhizosphere microbial communities towards a composition similar to PRCBC. This provides a feasible novel method for artificially and directionally driving microbial succession. In summary, we not only proposed a novel and efficient strategy for preparing stress resistant microbial communities to promote plant stress resistance, but also unexpectedly discovered a possible directionally driving method for soil microbial community succession.

Multi-stage aeration regime to regulate organic conversion toward gas alleviation and humification in food waste digestate composting

Aerobic composting has been considered as a pragmatic technique to convert food waste digestate into high-quality biofertiliser. Nevertheless, massive gaseous emission and immature product remain the primary challenges in food waste digestate composting. Thus, the performance of multi-stage aeration regimes to improve gaseous emissions and organic humification during food waste digestate composting was investigated in this study. In addition to continuous aeration with a constant intensity of 0.3 L kg·dry mass (DM)-1·min-1, two multi-stage decreased aeration regimes were designed as "0.3-0.2-0.1" and "0.3-0.1-0.1" L·kg·DM-1·min-1 from the thermophilic to cooling and then mature stages, respectively. Results showed that the decreased aeration regimes could alleviate nitrous oxide (N2O) and ammonia (NH3) emission and slightly enhance humification during composting. The alleviated N2O and NH3 emission were mainly contributed by abiotically reducing gaseous release potential as well as biotically inactivating denitrifers (Pusillimonas and Pseudidiomarina) and proliferating Atopobium to reduce nitrate availability under lower aeration supply. The "0.3-0.2-0.1 L kg·DM-1·min-1" regime exhibited a more excellent performance to alleviate N2O and NH3 emission by 27.5% and 16.3%, respectively. Moreover, the decreased aeration regimes also favored the enrichment of functional bacteria (Caldicoprobacter and Syntrophomonas) to accelerate lignocellulosic biodegradation and thus humic acid synthesis by 6.5%-11.2%. Given its better performance to improve gaseous emissions and humification, the aeration regime of "0.3-0.2-0.1 L kg·DM-1·min-1" are recommended in food waste digestate composting in practice.

Serratia spp. as plant growth-promoting bacteria alleviating salinity, drought, and nutrient imbalance stresses

In agricultural environments, plants are often exposed to abiotic stresses including temperature extremes, salt stress, drought, and heavy metal soil contamination, which leads to significant economic losses worldwide. Especially salt stress and drought pose serious challenges since they induce ionic toxicity, osmotic stress, and oxidative stress in plants. A potential solution can be the application of bacteria of the Serratia spp. known to promote plant growth under normal conditions Thus the mini-review aims to summarize the current knowledge on plant growth promotion by Serratia spp. (under the conditions of salinity stress, drought, and nutrient deficit) and highlight areas for development in the field. So far, it has been proven that Serratia spp. strains exhibit a variety of traits contributing to enhanced plant growth and stress tolerance, such as phytohormone production, ACC deaminase activity, nitrogen fixation, P and Zn solubilization, antioxidant properties improvement, and modulation of gene expression. Nevertheless, further research on Serratia spp. is needed, especially on two subjects: elucidating its mechanisms of action on plants at the molecular level and the effects of Serratia spp. on the indigenous soil and plant microbiota and, particularly, the rhizosphere. In both cases, it is advisable to use omics techniques to gain in-depth insights into the issues. Additionally, some strains of Serratia spp. may be phytopathogens, therefore studies to rule out this possibility are recommended prior to field trials. It is believed that by improving said knowledge the potential of Serratia spp. to stimulate plant growth will increase and strains from the genus will serve as an eco-friendly biofertilizer in sustainable agriculture more often.

Serratia marcescens LYGN1 Reforms the Rhizosphere Microbial Community and Promotes Cucumber and Pepper Growth in Plug Seedling Cultivation

The vegetable plug seedling plays an important role in improving vegetable production. The process of plug seedling contributes to high-quality vegetable seedlings. The substrate composition and chemical fertilizer are widely studied to promote seedling growth. However, little is known about the effect of beneficial bacteria in the rhizosphere microbial community and vegetables' growth during plug seedling. The use of beneficial microbes to promote vegetable seedling growth is of great potential. In this study, we showed that the Serratia marcescens strain LYGN1 enhanced the growth of cucumber and pepper seedlings in plug seedling cultivation. The treatment with LYGN1 significantly increased the biomass and the growth-related index of cucumber and pepper, improving the seedling quality index. Specifically, LYGN1 also improved the cucumber and pepper root system architecture and increased the root diameter. We applied high-throughput sequencing to analyze the microbial community of the seedlings' rhizosphere, which showed LYGN1 to significantly change the composition and structure of the cucumber and pepper rhizosphere microbial communities. The correlation analysis showed that the Abditibacteriota and Bdellovibrionota had positive effects on seedling growth. The findings of this study provide evidence for the effects of Serratia marcescens LYGN1 on the cucumber and pepper rhizosphere microbial communities, which also promoted seedling quality in plug seedling cultivation.

The Microbial Community Structure in the Rhizosphere of Theobroma cacao L. and Euterpe oleracea Mart. Is Influenced by Agriculture System in the Brazilian Amazon

This study tested the hypothesis that cocoa monoculture (MS) and cocoa-açai agroforestry systems (AFS) may influence the microbial community structure and populations of plant growth-promoting bacteria (PGPR). Accordingly, the aim was to analyze the microbial community structure and PGPR populations in different agroecosystems in the Brazilian Amazon. To achieve this, the rhizosphere microbial community of cocoa and açai plants in both Amazonian seasons (dry and rainy) was analyzed using culture-dependent (PGPR screening) and -independent methods [PCR-DGGE based on rrs, alp, nifH gene, and intergenic region (ITS) of fungi]. Concerning PGPR screening, out of 48 isolated bacterial strains, 25% were capable of siderophore production, 29% of mineralized organic phosphate, 8% of inorganic phosphate solubilization, and 4% of indole acetic acid production. Moreover, 17% of isolates could inhibit the growth of various phytopathogenic fungi. Statistical analyses of DGGE fingerprints (p < 0.05) showed that bacterial and fungal community structures in the rhizosphere were influenced by the seasons, supporting the results of the physicochemical analysis of the environment. Furthermore, as hypothesized, microbial communities differed statistically when comparing the MS and AFS. These findings provide important insights into the influence of climate and cultivation systems on soil microbial communities to guide the development of sustainable agricultural practices.

Prodigiosin from Serratia rubidaea MJ 24 impedes Helicoverpa armigera development by the dysregulation of Juvenile hormone-dopamine system

Prodigiosin pigment is a secondary metabolite produced by many bacterial species and is known for its medicinal properties. A few of these prodigiosin-producing bacteria are also reported to be entomopathogenic. It is intriguing to unravel the role of prodigiosin in insecticidal activities and its mode of action. In this study, we have shown the production and characterization of prodigiosin from the Serratia rubidaea MJ 24 isolated from the soil of the Western Ghats, India. Further, we assessed the effect of this pigment on the lepidopteran agricultural pest, Helicoverpa armigera. Prodigiosin-fed H. armigera indicated defective development of insect growth upon treatment. Due to defective early development, about 50% mortality and 40% reduction in body weight were observed in insects fed on a 500 ppm prodigiosin-containing diet. The transcriptomic analysis of these insects indicated significant dysregulation of Juvenile hormone synthesis and response related genes. In addition, dopamine related processes and their resultant melanization and sclerotization processes were also found to be affected. The changes in the expression levels of the key transcripts were further validated using real-time quantitative PCR. The metabolome data confirmed the developmental dysregulation of precursors and products of differentially regulated genes due to prodigiosin. Therefore, the corroborated data suggests that prodigiosin majorly affects H. armigera development through dysregulation of the Juvenile hormone-dopamine system and can be considered as a bioactive scaffold to design insect-pest management compounds. This study provides the first report of in-depth analysis of insecticidal system dynamics in H. armigera insects upon prodigiosin feeding via gene expression and metabolic change via omics approach.

Intermittent aeration to reduce gaseous emission and advance humification in food waste digestate composting: Performance and mechanisms

This study investigated the performance and mechanisms of intermittent aeration to regulate gaseous emission and humification during food waste digestate composting. In addition to continuous aeration, three intermittent aeration regimes were conducted with the on-off interval ratio at 3:1, 2:1, and 1:1 within each 30 min, respectively. Results showed that intermittent aeration regimes reduced gaseous emission and enhanced humification during composting. In particular, intermittent aeration with the on/off ratio of 1:1 was more effective to reduce organic mineralization than other regimes, which alleviated the emission of nitrous oxide and ammonia by 63.1% and 75.7% in comparison with continuous aeration, respectively. In addition, this aeration regime also enhanced the content of humic acid by 24.1%. Further analysis demonstrated that prolonging aeration-off intervals could enrich facultative bacteria (e.g. Atopobium and Clostridium) from digestate and inhibit the proliferation of several aerobic bacteria (e.g. Caldicoprobacter and Marinimicrobium) to retard organic mineralization for humification.

Efficacy of zinc oxide nanoparticles and Bifidobacterium bifidum Extraction on anaerobic bacteria isolated from patients with diarrhea

Infectious acute diarrhea may be prevented with probiotics; because they make up the majority of the colonic flora in breastfed newborns and are likely to contribute to the lower incidence of diarrhea in this population, Bifidobacteria are particularly appealing as probiotics agents. The present study was designed to identify anaerobic bacteria, especially C. difficile the main reason for dysentery associated with antibiotics. Detect the ability of each ZnoNPs and B. bifidum to inhibit bacterial growth. During the period from March to October 2019, (100) children and adults who came to Salah al-deen hospital in Tikrit city participated in the study under the supervision of a physician. All samples were transported using a carry Blair if late one or two hours after collection and culturing. The collected models were also cultured on Xylose Lysine Deoxycholate agar, Salmonella Shigella agar, Eosin methylene blue agar, and MacConkey agar. For initiated diagnoses of the Enterobacteriaceae, Blood agar is used to detect beta-hemolytic isolates, recover enteric bacteria other than Enterobacteriaceae, and evaluate the results of oxidase tests. To diagnose bacterium kinds, biochemical reactions and motility tests were used. Impact of ZnoNPs, and B. bifidum antibiotic In vitro. The results of 100 dysentery feces samples were obtained into (60%) samples for males and (40%) for females. Eighty-two positively impacted anaerobically on growth media like Clostridium complicate agar and MacConkey agar (18%) other than bacteria. In contrast, negative samples revealed 10 (55.56 percent) samples for males and 8 (44.44 percent) samples for females. The same stool samples were taken and cultured on Clostridium difficile agar and MacConkey agar under anaerobic and ideal incubation conditions. 15% and 67% of isolates appeared on MacConkey agar of the total number of samples, while 18% showed negative growth. Finally, Zn NPs showed their ability to inhibit Clostridium complicated segregate lean on the condensation 5 mg/ml, and it caused the inhibitory effect on Clostridium to complicate by 10-22 of the diameter of inhibition. The Inhibition Zone Dimeter ranged from 8 to 25 mm for isolates when condensation was utilized at 2.5 mg/ml. According to the findings, the widths of the inhibitory zones for isolates of C. difficile containing B. bifidum supernatant mg/ml ranged from 9 to 24 mm. Keywords: Zinc oxide nanoparticles, Probiotic, Bifidobacterium bifidum, Clostridium difficile

Autochthonous nutrient recycling driven by soil microbiota could be sustaining high coconut productivity in Lakshadweep Islands sans external fertilizer application

The soils of Lakshadweep Islands are formed as a result of the fragmentation of coral limestone, that is carbonate-rich, with neutral pH, but poor in plant nutrients. Coconut palm (Cocos nucifera L.) is the main crop cultivated, supporting the life and livelihood of the islanders. No external fertilizer application or major plant protection measures are adopted for their cultivation as the Islands were declared to go organic decades back. Yet, Lakshadweep has one of the highest productivity of coconut compared with other coconut growing areas in India. Therefore, a question arises: how is such a high coconut productivity sustained? We try to answer by estimating in three main islands (i) the nutrients added to the soil via the litter generated by coconut palms and (ii) the role of soil microbiota, including arbuscular mycorrhizae, for the high productivity. Our results indicated that, besides adding a substantial quantum of organic carbon, twice the needed amount of nitrogen, extra 20% phosphorus to the already P-rich soils, 43-45% of potassium required by palms could be easily met by the total coconut biomass residues returned to the soil. Principal Component Analysis showed that soil organic carbon %, potassium, and organic carbon added via the palm litter and AM spore load scored >± 0.95 in PC1, whereas, available K in the soil, bacteria, actinomycetes, phosphate solubilizers and fluorescent pseudomonads scored above >± 0.95 in PC2. Based on our analysis, we suggest that the autochthonous nutrients added via the coconut biomass residues, recycled by the soil microbial communities, could be one of the main reasons for sustaining a high productivity of the coconut palms in Lakshadweep Islands, in the absence of any external fertilizer application, mimicking a semi-closed-loop forest ecosystem.

Characterization of a novel chitinolytic Serratia marcescens strain TC-1 with broad insecticidal spectrum

The Gram-negative rod-shaped bacterium Serratia marcescens is an opportunistic pathogen of many organisms, including insects. We report the identification and optimal in vitro chitinase production conditions of a novel chitinolytic S. marcescens strain TC-1 isolated from a naturally infected white grub (Anomala corpulenta) collected from a peanut field at Nanyang city, Henan province, China. Strain identification was conducted by morphological, physiological, biochemical and molecular analyses. The amplified 16S rRNA gene of TC-1 showed a similarity greater than 99% with multiple strains of S. marcescens. Based on Neighbor-joining phylogenetic tree analysis of bacterial 16S rRNA gene sequences, TC-1 formed a clade with S. marcescens, clearly separated from other Serratia spp. The strain TC-1 showed larvicidal activities against five insect species (A. corpulenta, Plutella xylostella, Spodoptera exigua, Helicoverpa armigera, Bombyx mori) and the nematode Caenorhabditis elegans, but not against S. litura. The operating parameters of chitinase production by TC-1 were optimized by response surface methodology using a three-factor, three-level Box-Behnken experimental design. The effects of three independent variables i.e. colloidal chitin concentration (7–13 g l⁻¹), incubation time (24–72 h) and incubation temperature (24–32 °C) on chitinase production by TC-1 were investigated. A regression model was proposed to correlate the independent variables for an optimal chitinase activity predicted as 20.946 U ml⁻¹, using a combination of colloidal chitin concentration, incubation time and incubation temperature of 9.06 g l⁻¹, 63.83 h and 28.12 °C, respectively. The latter agreed well with a mean chitinase activity of 20.761 ± 0.102 U ml⁻¹ measured in the culture supernatants of TC-1 grown under similar conditions with a colloidal chitin concentration, incubation time and incubation temperature of 9 g l⁻¹, 64 h and 28 °C, respectively. Our study revealed the S. marcescens strain TC-1 with potential as a biocontrol agent of insect pests and nematodes and demonstrated the proposed regression model's potential to guide chitinase production by this strain.

Growth of ɣ-Proteobacteria in Low Salt Cucumber Fermentation Is Prevented by Lactobacilli and the Cover Brine Ingredients

This study investigated the ability of ɣ-proteobacteria, indigenous to fresh cucumber, to grow in the expressed fruit juice (CJM) and fermentation. It was hypothesized that fresh cucumbers can support prolific growth of ɣ-proteobacteria but that the cover brine composition and acid production by the competing lactobacilli in the fermentation of the fruit act as inhibitory agents. The ɣ-proteobacteria proliferated in CJM with an average maximum growth rate (μmax) of 0.3895 ± 0.0929 and doubling time (Td) of 1.885 ± 0.465/h. A significant difference was found between the ɣ-proteobacteria μmax and Td relative to Lactiplantibacillus pentosus LA0445 (0.2319 ± 0.019; 2.89/h) and Levilactobacillus brevis 7.2.43 (0.221 ± 0.015; 3.35/h) but not Lactiplantibacillus plantarum 3.2.8 (0.412 ± 0.119; 1.87/h). While inoculation level insignificantly altered the μmax and Td of the bacteria tested; it impacted the length of lag and stationary phases for the lactobacilli. Unlike the lactobacilli, the ɣ-proteobacteria were inhibited in CJM supplemented with a low salt fermentation cover brine containing calcium chloride, acetic acid and potassium sorbate. The ɣ-proteobacteria, P. agglomerans, was unable to proliferate in cucumber fermentations brined with calcium chloride at a pH of 6.0 ± 0.1 and the population of Enterobacteriaceae was outcompeted by the lactobacilli within 36 h. Together these observations demonstrate that the prolific growth of ɣ-proteobacteria in CJM is not replicated in cucumber fermentation. While the ɣ-proteobacteria growth rate is faster that most lactobacilli in CJM, their growth in cucumber fermentation is prevented by the cover brine and the acid produced by the indigenous lactobacilli. Thus, the lactobacilli indigenous to cucumber and cover brine composition influence the safety and quality of fermented cucumbers. IMPORTANCE While the abundance of specific ɣ-proteobacteria species varies among vegetable type, several harbor Enterobacteriaceae and Pseudomonadaceae that benefit the plant system. It is documented that such bacterial populations decrease in density early in vegetable fermentations. Consequently, it is assumed that they do not contribute to the quality of finished products. This study explored the viability of ɣ-proteobacteria in CJM, used as a model system, CJM supplemented with fermentation cover brine and cucumber fermentation, which are characterized by an extremely acidic endpoint pH (3.23 ± 0.17; n = 391). The data presented demonstrates that fresh cucumbers provide the nutrients needed by ɣ-proteobacteria to proliferate and reduce pH to 4.47 ± 0.12. However, ɣ-proteobacteria are unable to proliferate in cucumber fermentation. Control of ɣ-proteobacteria in fermentations depends on the cover brine constituents and the indigenous competing lactobacilli. This knowledge is of importance when developing guidelines for the safe fermentation of vegetables, particularly with low salt.

Minerals solubilizing and mobilizing microbiomes: A sustainable approaches for managing minerals deficiency in agricultural soil

Agriculture faces challenges to fulfill the rising food demand due to shortage of arable land and various environmental stressors. Traditional farming technologies help in fulfilling food demand but they are harmful to humans and environmental sustainability. The food production along with agro-environmental sustainability could be achieved by encouraging farmers to use agro-environmental sustainable products such as biofertilizers and biopesticides consisting of live microbes or plant extract instead of chemical-based inputs. The ecofriendly formulations play a significant role in plant growth promotion, crop yield, and repairing degraded soil texture and fertility sustainably. Mineral solubilizing microbes that provide vital nutrients like phosphorus, potassium, zinc, and selenium are essential for plant growth and development and could be developed as biofertilizers. These microbes could be plant-associated (rhizospheric, endophytic, and phyllospheric) or inhabits the bulk soil, and diverse extreme habitats. Mineral solubilizing microbes from soil, extreme environments, surface and internal parts of the plant belong to diverse phyla such as Ascomycota, Actinobacteria, Basidiomycota, Bacteroidetes, Chlorobi, Cyanobacteria, Chlorophyta, Euryarchaeota, Firmicutes, Gemmatimonadetes, Mucoromycota, Proteobacteria, and Tenericutes. Mineral solubilizing microbes (MSMs) directly or indirectly stimulate plant growth and development either by releasing plant growth regulators; solubilizing phosphorus, potassium, zinc, selenium, and silicon; biological nitrogen fixation; and production of siderophores, ammonia, hydrogen cyanide, hydrolytic enzymes, and bioactive compound/secondary metabolites. Biofertilizer developed using mineral solubilizing microbes is an eco-friendly solution to the sustainable food production system in many countries worldwide. The present review deals with the biodiversity of mineral solubilizing microbes, and potential roles in crop improvement and soil well-being for agricultural sustainability.

The endophytic bacterial entomopathogen Serratia marcescens promotes plant growth and improves resistance against Nilaparvata lugens in rice

Entomopathogenic bacteria are commonly used as biological agents to control different insect pests. However, little is known about the role of bacterial entomopathogens as endophytes in regulating both plant growth and resistance against insect pests. Here, we applied the entomopathogenic bacterium Serratia marcescens S-JS1 via rice seed inoculation and evaluated its effects on host plant growth and resistance against the rice pest Nilaparvata lugens. Furthermore, the induction of defense-related secondary metabolites by the bacterium was assessed by GC-MS/MS. We showed that S-JS1 was able to endophytically colonize the roots and shoots of rice seedlings following seed inoculation. Colonized plants showed increased seed germination (9.4-13.3 %), root (8.2-36.4 %) and shoot lengths (4.1-22.3 %), and root (26.7-69.3 %) and shoot fresh weights (19.0-49.0 %) compared to plants without inoculation. We also identified the production of indole-3-acetic acid by S-JS1, which is likely involved in enhancing rice plant growth. In a two-choice test, N. lugens adults preferred to feed on untreated control plants than on plants treated with S-JS1. In the no-choice feeding tests, the survival of N. lugens nymphs that fed on S-JS1-treated plants was significantly lower than that of nymphs that fed on untreated plants. Additionally, seeds treated with 10⁹ cfu/mL S-JS1 resulted in elevated levels of secondary metabolites, which may be associated with N. lugens resistance in rice plants. Therefore, we suggest that the entomopathogenic bacterium S. marcescens be considered a potentially promising endophyte for use in an innovative strategy for the integrated management of insect pests.

A comprehensive synthesis unveils the mysteries of phosphate-solubilizing microbes

Phosphate-solubilizing microbes (PSMs) drive the biogeochemical cycling of phosphorus (P) and hold promise for sustainable agriculture. However, their global distribution, overall diversity and application potential remain unknown. Here, we present the first synthesis of their biogeography, diversity and utility, employing data from 399 papers published between 1981 and 2017, the results of a nationwide field survey in China consisting of 367 soil samples, and a genetic analysis of 12986 genome-sequenced prokaryotic strains. We show that at continental to global scales, the population density of PSMs in environmental samples is correlated with total P rather than pH. Remarkably, positive relationships exist between the population density of soil PSMs and available P, nitrate-nitrogen and dissolved organic carbon in soil, reflecting functional couplings between PSMs and microbes driving biogeochemical cycles of nitrogen and carbon. More than 2704 strains affiliated with at least nine archaeal, 88 fungal and 336 bacterial species were reported as PSMs. Only 2.59% of these strains have been tested for their efficiencies in improving crop growth or yield under field conditions, providing evidence that PSMs are more likely to exert positive effects on wheat growing in alkaline P-deficient soils. Our systematic genetic analysis reveals five promising PSM genera deserving much more attention.

Endophytic bacteria from strawberry plants control gray mold in fruits via production of antifungal compounds against Botrytis cinerea L

Botrytis cinerea causes the gray mold disease in a wide range of plant hosts, especially in post-harvest periods. The control of this phytopathogen has been accomplished through the application of fungicides. However, this practice can cause environmental problems and increase fruit production costs. In addition, this fungus species has developed resistance to conventional synthetic fungicides. In this context, plant growth-promoting bacteria have shown potential for application in agricultural production because they are able to stimulate plant growth through different mechanisms, including the biological control of phytopathogens (indirect growth promotion mechanism). The aim of this work was to evaluate in vitro and in fruits the potential for indirect plant growth-promotion of bacteria isolated from strawberry leaves and roots. Dual plate method and inverted plate method were used to verify the ability of controlling in vitro the growth of Botrytis cinerea via the production of diffusible and volatile antifungal compounds, respectively. The effect of six bacterial isolates that showed greater potential for biological control in vitro was evaluated by scanning electron microscopy. Antifungal compounds produced by these bacterial isolates were identified by liquid chromatography coupled with mass spectrometry. Six bacterial strains were tested on strawberry pseudofruits. Five selected strains belong to the genus Bacillus and one to the genus Pantoea sp. Selected strains were able to inhibit more than 80 % of the mycelial growth of B. cinerea by the production of diffusible compounds and 90 % by volatile antifungal compounds production. Scanning electron microscopy showed the intense degradation of fungal hyphae caused by the presence of all bacterial strains. Bioactive compounds (salycilamide, maculosin, herniarin, lauroyl diethanolamide, baptifoline, undecanedioic acid, botrydial, 8 3-butylidene-7-hydroxyphthalide and N-(3-oxo-henoyl)-homoserine lactone) were obtained from liquid culture of these strains and extraction with ethyl acetate. All six isolates tested in vivo reduced the incidence of gray mold in strawberry pseudofruits in postharvest. It is concluded that isolates 26, 29, 65, 69, 132 (Bacillus sp.) and MQT16M1 (Pantoea sp.) have potential application for the biological control of Botrytis cinerea in strawberry via the production of diffusible and volatile antifungal compounds.

Mechanism of interaction of an endofungal bacterium Serratia marcescens D1 with its host and non-host fungi

Association of bacteria with fungi is a major area of research in infection biology, however, very few strains of bacteria have been reported that can invade and reside within fungal hyphae. Here, we report the characterization of an endofungal bacterium Serratia marcescens D1 from Mucor irregularis SS7 hyphae. Upon re-inoculation, colonization of the endobacterium S. marcescens D1 in the hyphae of Mucor irregularis SS7 was demonstrated using stereo microscopy. However, S. marcescens D1 failed to invade into the hyphae of the tested Ascomycetes (except Fusarium oxysporum) and Basidiomycetes. Remarkably, Serratia marcescens D1 could invade and spread over the culture of F. oxysporum that resulted in mycelial death. Prodigiosin, the red pigment produced by the Serratia marcescens D1, helps the bacterium to invade fungal hyphae as revealed by the increasing permeability in fungal cell membrane. On the other hand, genes encoding the type VI secretion system (T6SS) assembly protein TssJ and an outer membrane associated murein lipoprotein also showed significant up-regulation during the interaction process, suggesting the involvement of T6SS in the invasion process.

Multi-trait PGP rhizobacterial endophytes alleviate drought stress in a senescent genotype of sorghum [Sorghum bicolor (L.) Moench]

Root-tissue colonizing bacteria demonstrated with multiple PGP traits from sorghum plants were identified as Ochrobactrum sp. EB-165, Microbacterium sp. EB-65, Enterobacter sp. EB-14 and Enterobacter cloacae strain EB-48 on the basis of 16S rRNA gene sequencing. Here, the in vivo experiments using ½-MS media and ½-MS media + 15% PEG 8000 (for inducing drought stress) indicated stress tolerance imparting ability of these rhizobacterial endophytes in a non-stay green and senescent genotype (R-16) of sorghum. In the experiment with sterile soilrite mix base, seed bacterization with these isolates showed improved plant growth specifically the roots, in terms of root length (~ 44.2 to 50.8% over controls), root dry weight (~ 91.3 to 99.8% over controls) and root surface area (~ 1 to 1.5 fold over controls) under drought stress. Rhizobacterial endophytes were successful, not only in providing better cellular osmotic adjustment in leaves (≥ 1-fold increase in proline accumulation over controls), but favorable physiological responses like Relative Water Content (RWC) and cell Membrane Stability Index (MSI) in the inoculated plants during the drought stress induction. Up-regulation of drought responsive genes like sbP5CS2 and sbP5CS1 was observed in these endophytes-treated plants as compared to untreated control and Escherichia coli DH5α (negative control)-treated plants. Interestingly, the stress imparting traits of rhizobacterial endophytes, including up-regulation of specific genes, were observed during sorghum seedling growth only under drought stresses. The results of this study lead to the conclusion that the potential endophytic rhizobacterial interactions can contribute to plant growth promotion as well as induced stress tolerance in sorghum.

Açaí palm seedling growth promotion by rhizobacteria inoculation

Lower growth rate of the açaí palm seedlings limits the crops' commercial expansion. The goal was evaluating the biometry, biomass accumulation, nutrient contents, chlorophyll-a fluorescence, and gas exchange in açaí seedlings inoculated with rhizobacteria. The treatments were individual inoculations of the seven rhizobacteria isolates and one control (without inoculation) on the roots. Biometry and biomass data were submitted to cluster analysis to separate the isolates into groups according to the similarity degree, and groups' means were compared through the SNK test. Three groups were formed; group 1 was composed of the control; group 2 of the UFRA-35, UFRA-38, UFRA-58, UFRA-61, UFRA-92, and BRM-32111 isolates; and group 3 was composed of the BRM-32113 isolate. Group 2 and 3 isolates promoted an increase in growth, biomass accumulation, higher levels of nutrients and chlorophyll, and improvements in the gas exchange and chlorophyll-a fluorescence in comparison with the control. The results evidenced that the rhizobacteria accelerate the growth, increase the photosynthetic efficiency, and induce the leaf nutrient accumulation in açaí palm seedlings. The rhizobacteria inoculation can contribute to the sustainable management of the açaí palm seedling production in nurseries.

Application of filamentous phages in environment: A tectonic shift in the science and practice of ecorestoration

Theories in soil biology, such as plant-microbe interactions and microbial cooperation and antagonism, have guided the practice of ecological restoration (ecorestoration). Below-ground biodiversity (bacteria, fungi, invertebrates, etc.) influences the development of above-ground biodiversity (vegetation structure). The role of rhizosphere bacteria in plant growth has been largely investigated but the role of phages (bacterial viruses) has received a little attention. Below the ground, phages govern the ecology and evolution of microbial communities by affecting genetic diversity, host fitness, population dynamics, community composition, and nutrient cycling. However, few restoration efforts take into account the interactions between bacteria and phages. Unlike other phages, filamentous phages are highly specific, nonlethal, and influence host fitness in several ways, which make them useful as target bacterial inocula. Also, the ease with which filamentous phages can be genetically manipulated to express a desired peptide to track and control pathogens and contaminants makes them useful in biosensing. Based on ecology and biology of filamentous phages, we developed a hypothesis on the application of phages in environment to derive benefits at different levels of biological organization ranging from individual bacteria to ecosystem for ecorestoration. We examined the potential applications of filamentous phages in improving bacterial inocula to restore vegetation and to monitor changes in habitat during ecorestoration and, based on our results, recommend a reorientation of the existing framework of using microbial inocula for such restoration and monitoring. Because bacterial inocula and biomonitoring tools based on filamentous phages are likely to prove useful in developing cost-effective methods of restoring vegetation, we propose that filamentous phages be incorporated into nature-based restoration efforts and that the tripartite relationship between phages, bacteria, and plants be explored further. Possible impacts of filamentous phages on native microflora are discussed and future areas of research are suggested to preclude any potential risks associated with such an approach.

Evaluation of the biocontrol efficacy of a Serratia marcescens strain indigenous to tea rhizosphere for the management of root rot disease in tea

The aim of the present study is to evaluate plant growth promoting and biocontrol efficacy of a Serratia marcescens strain ETR17 isolated from tea rhizosphere for the effective management of root rot disease in tea. Isolated bacterial culture ETR17 showed significant level of in vitro antagonism against nine different foliar and root pathogens of tea. The phenotypic and molecular characterization of ETR17 revealed the identity of the bacterium as Serratia marcescens. The bacterium was found to produce several hydrolytic enzymes like chitinase, protease, lipase, cellulase and plant growth promoting metabolites like IAA and siderophore. Scanning electron microscopic studies on the interaction zone between pathogen and antagonistic bacterial isolate revealed severe deformities in the fungal mycelia. Spectral analyses (LC-ESI-MS, UV-VIS spectrophotometry and HPLC) and TLC indicated the presence of the antibiotics pyrrolnitrin and prodigiosin in the extracellular bacterial culture extracts. Biofilm formation by ETR17 on polystyrene surface was also observed. In vivo application of talc-based formulations prepared with the isolate ETR17 in tea plantlets under green house conditions revealed effective reduction of root-rot disease as well as plant growth promotion to a considerable extent. Viability studies with the ETR17 talc formulation showed the survivability of the isolate up to six months at room temperature. The sustenance of ETR17 (concentration of 8-9x108 cfu g-1) in the soil after the application of talc formulation was recorded by ELISA. Safety studies revealed that ETR17 did not produce hemolysin as observed in pathogenic Serratia strains. The biocontrol strain reported in this study can be used for field application in order to minimize the use of chemical fungicides for disease control in tea gardens.

Isolation of vanadium-resistance endophytic bacterium PRE01 from Pteris vittata in stone coal smelting district and characterization for potential use in phytoremediation

This study investigates the V-resistant endophytic bacteria isolated from V-accumulator Pteris vittata grown on stone coal smelting district. Among all the ten isolates, the strain PRE01 identified as Serratia marcescens ss marcescens by Biolog GEN III MicroPlate™ was screened out by ranking first in terms of heavy metal resistance and plant growth promoting traits. The S. marcescens PRE01 had strong V, Cr and Cd resistance especially for V up to 1500mg/L. In addition, it exhibited ACC deaminase activity, siderophore production and high indoleacetic acid production (60.14mg/L) and solubilizing P potential (336.41mg/L). For heavy metal detoxification tests, PRE01 could specifically assimilate 97.6%, 21.7% and 6.6% of Cd(II), Cr(VI) and V(V) within 72h incubation. Despite the poor absorption of the two anions, most V(V) and Cr(VI) were detoxified and reduced to lower valence states by the strain. Furthermore, the isolate had the potential to facilitate the metals uptake of their hosts by changing heavy metal speciation. Our research may open up further scope of utilizing the endophyte for enhancing phytoextraction of vanadium industry contaminated soils.

Evaluation of multifarious plant growth promoting traits, antagonistic potential and phylogenetic affiliation of rhizobacteria associated with commercial tea plants grown in Darjeeling, India

Plant growth promoting rhizobacteria (PGPR) are studied in different agricultural crops but the interaction of PGPR of tea crop is not yet studied well. In the present study, the indigenous tea rhizobacteria were isolated from seven tea estates of Darjeeling located in West Bengal, India. A total of 150 rhizobacterial isolates were screened for antagonistic activity against six different fungal pathogens i.e. Nigrospora sphaerica (KJ767520), Pestalotiopsis theae (ITCC 6599), Curvularia eragostidis (ITCC 6429), Glomerella cingulata (MTCC 2033), Rhizoctonia Solani (MTCC 4633) and Fusarium oxysporum (MTCC 284), out of which 48 isolates were antagonist to at least one fungal pathogen used. These 48 isolates exhibited multifarious antifungal properties like the production of siderophore, chitinase, protease and cellulase and also plant growth promoting (PGP) traits like IAA production, phosphate solubilization, ammonia and ACC deaminase production. Amplified ribosomal DNA restriction analysis (ARDRA) and BOX-PCR analysis based genotyping clustered the isolates into different groups. Finally, four isolates were selected for plant growth promotion study in two tea commercial cultivars TV-1 and Teenali-17 in nursery conditions. The plant growth promotion study showed that the inoculation of consortia of these four PGPR isolates significantly increased the growth of tea plant in nursery conditions. Thus this study underlines the commercial potential of these selected PGPR isolates for sustainable tea cultivation.

Diversity of nodular bacteria ofScorpiurus muricatusin western Algeria and their impact on plant growth

A total of 51 bacterial strains were isolated from root nodules of Scorpiurus muricatus sampled from 6 regions of western Algeria. Strain diversity was assessed by rep-PCR amplification fingerprinting, which grouped the isolates into 28 different clusters. Partial nucleotide sequencing of the 16S rRNA gene and BLAST analysis revealed that root nodules of S. muricatus were colonized by different species close to Rhizobium vignae, Rhizobium radiobacter, Rhizobium leguminosarum, Phyllobacterium ifriqiyense, Phyllobacterium endophyticum, Starkeya sp., and Pseudomonas sp. However, none of these strains was able to form nodules on its host plant; even nodC was present in a single strain (SMT8a). The inoculation test showed a great improvement in the growth of inoculated plants compared with noninoculated control plants. A significant amount of indole acetic acid was produced by some strains, but only 2 strains could solubilize phosphate. In this report we described for the first time the diversity of bacteria isolated from root nodules of S. muricatus growing in different regions in western Algeria and demonstrated their potential use in promoting plant growth.

Plant Growth Promoting Bacteria Associated with Langsdorffia hypogaea-Rhizosphere-Host Biological Interface: A Neglected Model of Bacterial Prospection

Soil is a habitat where plant roots and microorganisms interact. In the region of the Brazilian Iron Quadrangle (IQ), studies involving the interaction between microbiota and plants have been neglected. Even more neglected are the studies involving the holoparasite plant Langsdorffia hypogaea Mart. (Balanophoraceae). The geomorphological peculiarities of IQ soil, rich in iron ore, as well as the model of interaction between L. hypogaea, its hosts and the soil provide a unique niche that acts as selective pressure to the evolution of plant growth-promoting bacteria (PGPB). The aim of this study was to prospect the bacterial microbiota of holoparasitic plant L. hypogaea, its plant host and corresponding rhizosphere of IQ soil, and to analyze the potential of these isolates as PGPB. We obtained samples of 11 individuals of L. hypogaea containing fragments of host and rhizosphere remnants, resulting in 81 isolates associated with Firmicutes and Proteobacteria phyla. The ability to produce siderophores, hydrocyanic acid (HCN), indole-3-acetic acid (IAA), nitrogen (N₂) fixation, hydrolytic enzymes secretion and inhibition of enteropathogens, and phytopathogens were evaluated. Of the total isolates, 62, 86, and 93% produced, respectively, siderophores, IAA, and were able to fix N₂. In addition, 27 and 20% of isolates inhibited the growth of enteropathogens and phytopathogens, respectively, and 58% were able to produce at least one hydrolytic activity investigated. The high number of isolates that produce siderophores and indole-3-acetic acid suggests that this microbiota may be important for adaptation of plants to IQ. The results demonstrate for the first time the biological importance of Brazilian IQ species as reservoirs of specific microbiotas that might be used as PGPB on agricultural land or antropized soils that needs to be reforested.

The Multifarious PGPR Serratia marcescens CDP-13 Augments Induced Systemic Resistance and Enhanced Salinity Tolerance of Wheat (Triticum aestivum L.)

The present study demonstrates the plant growth promoting (PGP) potential of a bacterial isolate CDP-13 isolated from ‘Capparis decidua’ plant, and its ability to protect plants from the deleterious effect of biotic and abiotic stressors. Based on 16S rRNA gene sequence analysis, the isolate was identified as Serratia marcescens. Among the PGP traits, the isolate was found to be positive for ACC deaminase activity, phosphate solubilization, production of siderophore, indole acetic acid production, nitrogen fixation, and ammonia production. CDP-13 showed growth at an increased salt (NaCl) concentration of up to 6%, indicating its potential to survive and associate with plants growing in saline soil. The inoculation of S. marcescens enhanced the growth of wheat plant under salinity stress (150–200 mM). It significantly reduced inhibition of plant growth (15 to 85%) caused by salt stressors. Application of CDP-13 also modulated concentration (20 to 75%) of different osmoprotectants (proline, malondialdehyde, total soluble sugar, total protein content, and indole acetic acid) in plants suggesting its role in enabling plants to tolerate salt stressors. In addition, bacterial inoculation also reduced the disease severity caused by fungal infection, which illustrated its ability to confer induced systemic resistance (ISR) in host plants. Treatment of wheat plants with the test organism caused alteration in anti-oxidative enzymes activities (Superoxide dismutase, Catalase, and Peroxidase) under various salinity levels, and therefore minimizes the salinity-induced oxidative damages to the plants. Colonization efficiency of strain CDP-13 was confirmed by CFU count, epi-fluorescence microscopy, and ERIC-PCR-based DNA fingerprinting approach. Hence, the study indicates that bacterium CDP-13 enhances plant growth, and has potential for the amelioration of salinity stress in wheat plants. Likewise, the results also provide insights into biotechnological approaches to using PGPR as an alternative to chemicals and pesticides.

Association of plant growth-promoting Serratia spp. with the root nodules of chickpea

Serratia species-affiliated DNA sequences have recently been discovered in the root nodules of two chickpea cultivars; however, little is known about their potential influence on chickpea plant growth. All Serratia-affiliated sequences (1136) could be grouped into two clusters at 98% DNA similarity. The major cluster, represented by 96% of sequences, was closely associated with Serratia marcescens sequences from GenBank. In the current study, we isolated two Serratia strains, 5D and RTL100, from root nodules of a field-grown Desi cultivar from Faisalabad and Thal areas, respectively. In vitro, strain 5D showed significantly higher phosphate (P) solubilization and lactic acid production than RTL100, whereas a comparable concentration of phytohormone was produced by both isolates. The application of Serratia strain 5D as an inoculum resulted in 25.55% and 30.85% increases in the grain yield of crops grown on fertile soil in irrigated areas and nutrient-deficient soil in rainfed areas, respectively, compared to the non-inoculated control. Results of plant inoculations indicated that Serratia sp. 5D and RTL100 can serve as effective microbial inoculants, particularly in nutrient-deficient soils in rainfed areas, where chickpea is the only major crop grown during the entire year.

Oasis desert farming selects environment-specific date palm root endophytic communities and cultivable bacteria that promote resistance to drought

Oases are desert-farming agro-ecosystems, where date palm (Phoenix dactylifera L.) plays a keystone role in offsetting the effects of drought and maintaining a suitable microclimate for agriculture. At present, abundance, diversity and plant growth promotion (PGP) of date palm root-associated bacteria remain unknown. Considering the environmental pressure determined by the water scarcity in the desert environments, we hypothesized that bacteria associated with date palm roots improve plant resistance to drought. Here, the ecology of date palm root endophytes from oases in the Tunisian Sahara was studied with emphasis on their capacity to promote growth under drought. Endophytic communities segregated along a north-south gradient in correlation with geo-climatic parameters. Screening of 120 endophytes indicated that date palm roots select for bacteria with multiple PGP traits. Bacteria rapidly cross-colonized the root tissues of different species of plants, including the original Tunisian date palm cultivar, Saudi Arabian cultivars and Arabidopsis. Selected endophytes significantly increased the biomass of date palms exposed to repeated drought stress periods during a 9-month greenhouse experiment. Overall, results indicate that date palm roots shape endophytic communities that are capable to promote plant growth under drought conditions, thereby contributing an essential ecological service to the entire oasis ecosystem.

Microbial population dynamics in response to Pectobacterium atrosepticum infection in potato tubers

Endophytes are microbes and fungi that live inside plant tissues without damaging the host. Herein we examine the dynamic changes in the endophytic bacterial community in potato (Solanum tuberosum) tuber in response to pathogenic infection by Pectobacterium atrosepticum, which causes soft rot in numerous economically important crops. We quantified community changes using both cultivation and next-generation sequencing of the 16S rRNA gene and found that, despite observing significant variability in both the mass of macerated tissue and structure of the endophytic community between individual potato tubers, P. atrosepticum is always taken over by the endophytes during maceration. 16S rDNA sequencing revealed bacteria from the phyla Proteobacteria, Actinobacteria, Firmicutes, Bacteroidetes, Fusobacteria, Verrucomicrobia, Acidobacteria, TM7, and Deinococcus-Thermus. Prior to infection, Propionibacterium acnes is frequently among the dominant taxa, yet is out competed by relatively few dominant taxa as the infection proceeds. Two days post-infection, the most abundant sequences in macerated potato tissue are Gammaproteobacteria. The most dominant genera are Enterobacter and Pseudomonas. Eight days post-infection, the number of anaerobic pectolytic Clostridia increases, probably due to oxygen depletion. These results demonstrate that the pathogenesis is strictly initiated by the pathogen (sensu stricto) and proceeds with a major contribution from the endophytic community.

Microbiota from Meloidogyne exigua egg masses and evidence for the effect of volatiles on infective juvenile survival

Egg masses ofMeloidogyne exiguafrom coffee plants are subjected to a range of microbial populations and these resident soil organisms in the egg masses may affect nematode communities. The incidence of fungi and bacteria inM. exiguaegg masses was investigated and the toxic effect of their volatile organic compounds (VOCs) was tested on second-stage juveniles (J2). Bacteria and fungi were isolated from egg masses on coffee root and identified to species. The nematicidal activity of VOCs from bacterial and fungal strains was tested againstM. exiguainin vitroexperiments. Several bacterial and fungal strains were found inM. exiguaegg masses and produced VOCs that were toxic toM. exiguaJ2. Bacterial strains induced more nematode mortality compared with fungal strains. The continued colonisation of fungi and bacteria inM. exiguaegg masses occurred during the year and their VOCs reduced the viable inocula ofM. exiguaand should be explored as biocontrol agents.

Whole genome sequencing and analysis of plant growth promoting bacteria isolated from the rhizosphere of plantation crops coconut, cocoa and arecanut

Coconut, cocoa and arecanut are commercial plantation crops that play a vital role in the Indian economy while sustaining the livelihood of more than 10 million Indians. According to 2012 Food and Agricultural organization's report, India is the third largest producer of coconut and it dominates the production of arecanut worldwide. In this study, three Plant Growth Promoting Rhizobacteria (PGPR) from coconut (CPCRI-1), cocoa (CPCRI-2) and arecanut (CPCRI-3) characterized for the PGP activities have been sequenced. The draft genome sizes were 4.7 Mb (56% GC), 5.9 Mb (63.6% GC) and 5.1 Mb (54.8% GB) for CPCRI-1, CPCRI-2, CPCRI-3, respectively. These genomes encoded 4056 (CPCRI-1), 4637 (CPCRI-2) and 4286 (CPCRI-3) protein-coding genes. Phylogenetic analysis revealed that both CPCRI-1 and CPCRI-3 belonged to Enterobacteriaceae family, while, CPCRI-2 was a Pseudomonadaceae family member. Functional annotation of the genes predicted that all three bacteria encoded genes needed for mineral phosphate solubilization, siderophores, acetoin, butanediol, 1-aminocyclopropane-1-carboxylate (ACC) deaminase, chitinase, phenazine, 4-hydroxybenzoate, trehalose and quorum sensing molecules supportive of the plant growth promoting traits observed in the course of their isolation and characterization. Additionally, in all the three CPCRI PGPRs, we identified genes involved in synthesis of hydrogen sulfide (H2S), which recently has been proposed to aid plant growth. The PGPRs also carried genes for central carbohydrate metabolism indicating that the bacteria can efficiently utilize the root exudates and other organic materials as energy source. Genes for production of peroxidases, catalases and superoxide dismutases that confer resistance to oxidative stresses in plants were identified. Besides these, genes for heat shock tolerance, cold shock tolerance and glycine-betaine production that enable bacteria to survive abiotic stress were also identified.

Identification and characterization of endophytic bacteria from corn (Zea mays L.) roots with biotechnological potential in agriculture

Six endophytic bacteria of corn roots were identified as Bacillus sp. and as Enterobacter sp, by sequencing of the 16S rRNA gene. Four of the strains, CNPSo 2476, CNPSo 2477, CNPSo 2478 and CNPSo 2480 were positive for the nitrogen fixation ability evaluated through the acetylene reduction assay and amplification of nifH gene. Two Bacillus strains (CNPSo 2477 and CNPSo 2478) showed outstanding skills for the production of IAA, siderophores and lytic enzymes, but were not good candidates as growth promoters, because they reduced seed germination. However, the same strains were antagonists against the pathogenic fungi Fusarium verticillioides, Colletotrichum graminicola, Bipolaris maydis and Cercospora zea-maydis. As an indication of favorable bacterial action, Enterobacter sp. CNPSo 2480 and Bacillus sp. CNPSo 2481 increased the root volume by 44% and 39%, respectively, and the seed germination by 47% and 56%, respectively. Therefore, these two strains are good candidates for future testing as biological inoculants for corn.