Genome-guided insights of tropical Bacillus strains efficient in maize growth promotion.

Plant growth promoting bacteria (PGPB) are an efficient and sustainable alternative to mitigate biotic and abiotic stresses in maize. This work aimed to sequence the genome of two Bacillus strains (B116 and B119) and to evaluate their plant growth-promoting (PGP) potential in vitro and their capacity to trigger specific responses in different maize genotypes. Analysis of the genomic sequences revealed the presence of genes related to PGP activities. Both strains were able to produce biofilm and exopolysaccharides, and solubilize phosphate. The strain B119 produced higher amounts of IAA-like molecules and phytase, whereas B116 was capable to produce more acid phosphatase. Maize seedlings inoculated with either strains were submitted to polyethylene glycol-induced osmotic stress and showed an increase of thicker roots, which resulted in a higher root dry weight. The inoculation also increased the total dry weight and modified the root morphology of 16 out of 21 maize genotypes, indicating that the bacteria triggered specific responses depending on plant genotype background. Maize root remodeling was related to growth promotion mechanisms found in genomic prediction and confirmed by in vitro analysis. Overall, the genomic and phenotypic characterization brought new insights to the mechanisms of PGP in tropical Bacillus.

Selection and molecular characterization of Bacillus thuringiensis strains efficient against soybean looper (Chrysodeixis includens) and Spodoptera species

ABSTRACT Soybean looper (Chrysodeixis includens) and Spodoptera group are important defoliators insects responsible for significant yield losses in soybean, cotton and maize in Brazil. Bioinsecticides and transgenic plants expressing insecticidal proteins from Bacillus thuringiensis are among the most used sustainable control methods for pest control in agriculture, especially for several lepidopteran species. To provide new components for insect control, this study aimed to select and characterize B. thuringiensis strains toxic to C. includens, S. cosmioides, S. eridania, and S. frugiperda. We performed initial bioassays with fifty B. thuringiensis strains for C. includens and selected four strains - 1608A, 726, 773, and 775E - that caused high larval mortality (100%) to be tested against Spodoptera species. These strains harbored cry insecticidal genes, megaplasmids, absence of β-exotoxin and showed two major proteins about 65 and 130 kDa in SDS-page attributed to Cry protein classes toxic to lepidopteran species. The 1608A and 775E strains also showed high toxicity to Spodoptera species that demonstrate great potential for B. thuringiensis-based bioproduct development and as sources of new insecticidal genes for transgenic crops for multiple pest control relevant in the Brazilian agricultural system.

Endophytic Bacillus strains enhance pearl millet growth and nutrient uptake under low-P.

Bacterial endophytes are considered to have a beneficial effect on host plants, improving their growth by different mechanisms. The objective of this study was to investigate the capacity of four endophytic Bacillus strains to solubilize iron phosphate (Fe-P), produce siderophores and indole-acetic acid (IAA) in vitro, and to evaluate their plant growth promotion ability in greenhouse conditions by inoculation into pearl millet cultivated in a P-deficient soils without P fertilization, with Araxá rock phosphate or soluble triple superphosphate. All strains solubilized Fe-P and three of them produced carboxylate-type siderophores and high levels of IAA in the presence of tryptophan. Positive effect of inoculation of some of these strains on shoot and root dry weight and the N P K content of plants cultivated in soil with no P fertilization might result from the synergistic combination of multiple plant growth promoting (PGP) traits. Specifically, while B1923 enhanced shoot and root dry weight and root N P content of plants cultivated with no P added, B2084 and B2088 strains showed positive performance on biomass production and accumulation of N P K in the shoot, indicating that they have higher potential to be microbial biofertilizer candidates for commercial applications in the absence of fertilization.

Endophytic Bacillus strains enhance pearl millet growth and nutrient uptake under low-P

Abstract Bacterial endophytes are considered to have a beneficial effect on host plants, improving their growth by different mechanisms. The objective of this study was to investigate the capacity of four endophytic Bacillus strains to solubilize iron phosphate (Fe-P), produce siderophores and indole-acetic acid (IAA) in vitro, and to evaluate their plant growth promotion ability in greenhouse conditions by inoculation into pearl millet cultivated in a P-deficient soils without P fertilization, with Araxá rock phosphate or soluble triple superphosphate. All strains solubilized Fe-P and three of them produced carboxylate-type siderophores and high levels of IAA in the presence of tryptophan. Positive effect of inoculation of some of these strains on shoot and root dry weight and the N P K content of plants cultivated in soil with no P fertilization might result from the synergistic combination of multiple plant growth promoting (PGP) traits. Specifically, while B1923 enhanced shoot and root dry weight and root N P content of plants cultivated with no P added, B2084 and B2088 strains showed positive performance on biomass production and accumulation of N P K in the shoot, indicating that they have higher potential to be microbial biofertilizer candidates for commercial applications in the absence of fertilization.

Endophytic Bacillus strains enhance pearl millet growth and nutrient uptake under low-P

Abstract Bacterial endophytes are considered to have a beneficial effect on host plants, improving their growth by different mechanisms. The objective of this study was to investigate the capacity of four endophytic Bacillus strains to solubilize iron phosphate (Fe-P), produce siderophores and indole-acetic acid (IAA) in vitro, and to evaluate their plant growth promotion ability in greenhouse conditions by inoculation into pearl millet cultivated in a P-deficient soils without P fertilization, with Araxá rock phosphate or soluble triple superphosphate. All strains solubilized Fe-P and three of them produced carboxylate-type siderophores and high levels of IAA in the presence of tryptophan. Positive effect of inoculation of some of these strains on shoot and root dry weight and the N P K content of plants cultivated in soil with no P fertilization might result from the synergistic combination of multiple plant growth promoting (PGP) traits. Specifically, while B1923 enhanced shoot and root dry weight and root N P content of plants cultivated with no P added, B2084 and B2088 strains showed positive performance on biomass production and accumulation of N P K in the shoot, indicating that they have higher potential to be microbial biofertilizer candidates for commercial applications in the absence of fertilization.

Quantitative Trait Loci and Resistance Gene Analogs Associated with Maize White Spot Resistance.

Maize white spot (MWS), caused by the bacterium Pantoea ananatis, is one of the most important maize foliar diseases in tropical and subtropical regions, causing significant yield losses. Despite its economic importance, genetic studies of MWS are scarce. The aim of this study was to map quantitative trait loci (QTL) associated with MWS resistance and to identify resistance gene analogs (RGA) underlying these QTL. QTL mapping was performed in a tropical maize F2:3 population, which was genotyped with simple-sequence repeat and RGA-tagged markers and phenotyped for the response to MWS in two Brazilian southeastern locations. Nine QTL explained approximately 70% of the phenotypic variance for MWS resistance at each location, with two of them consistently detected in both environments. Data mining using 112 resistance genes cloned from different plant species revealed 1,697 RGA distributed in clusters within the maize genome. The RGA Pto19, Pto20, Pto99, and Xa26.151.4 were genetically mapped within MWS resistance QTL on chromosomes 4 and 8 and were preferentially expressed in the resistant parental line at locations where their respective QTL occurred. The consistency of QTL mapping, in silico prediction, and gene expression analyses revealed RGA and genomic regions suitable for marker-assisted selection to improve MWS resistance.

Molecular analysis of endophytic bacteria from the genus Bacillus isolated from tropical maize (Zea mays L. ) / Análise molecular de bactérias endofíticas do gênero Bacillus isoladas de milho tropical (Zea mays L. )

Endophytic bacteria play an important role in agriculture by improving plant performance and adaptation against biotic and abiotic stresses. In the present study molecular methods were used for identifying Bacillus endophytic bacteria isolated from Brazilian sweet corn. SDS-PAGE of wholecell protein extract of fortytwo isolates revealed a high number of scrutinable bands. Twenty-four isolates were identified in nine different groups of duplicated bacteria and eighteen were identified as unique. Some high-accumulated polipeptides with variable length were observed in almost isolates. Partial sequencing of 16S ribosomal gene revealed that all isolates are Bacillus sp. and among thirteen isolates with similar protein profiles, two were different strains. Among the forty-two isolates identified by rDNA sequencing, Bacillus subitilis and B. pumilus were the most frequenty species (15 and 12 isolates, respectively) followed by B. licheniformes (7 isolates), B. cereus (5 isolates) and B. amiloliquefascens (3 isolates). According to present results, SDS-PAGE technique could be used as a fast and cheap first tool for identifying interspecific variation in maize endophytic bacterial collections while rDNA sequencing could be applied for analyzing intraspecific variation among isolates with similar protein profile as well as for taxonomic studies.

Bactérias endofíticas desempenham papel importante na agricultura, melhorando a performance e adaptação de plantas contra estresses bióticos e abióticos. No presente estudo, métodos moleculares foram empregados para identificar bactérias endofíticas do gênero Bacillus isoladas de cultivares de milho doce brasileiro. SDS-PAGE de extratos protéicos totais de quarenta e dois isolados revelaram elevado número de bandas escrutináveis. Vinte e quatro isolados formaram nove grupos diferentes de réplicas bactérianas e dezoito foram considerados como únicos. Entre os isolados, alguns polipeptídios, de tamanhos variados, foram altamente acumulados. Seqüenciamento parcial do gene ribosomal 16S revelou que todos os isolados pertencem ao gênero Bacillus e que, entre treze isolados com padrão protéico similar, dois eram linhagens diferentes. Entre os quarenta e dois isolados identificados por seqüenciamento de rDNA, Bacillus subtilis e B. pumilus foram mais frequentes (15 e 12 isolados, respectivamente), seguido por, B. licheniformes (7 isolados), B. cereus (5 isolados) e B. amiloliquefascens (3 isolados). Baseado nos resultados, conclui-se que a técnica de SDS-PAGE poderá ser usada como primeiro procedimento, rápido e barato, para identificar variação inter-específica em coleções de bactérias endofíticas isoladas do milho, enquanto o método de seqüenciamento de rDNA poderá ser aplicado para analisar variações intra-específica entre isolados com padões similares de proteínas e estudos de taxonomia.