Bacteria that colonize plant roots and promote plant growth are referred to as plant growth-promoting rhizobacteria (PGPR). PGPR are highly diverse and in this review we focus on rhizobacteria as ...biocontrol agents. Their effects can occur via local antagonism to soil-borne pathogens or by induction of systemic resistance against pathogens throughout the entire plant. Several substances produced by antagonistic rhizobacteria have been related to pathogen control and indirect promotion of growth in many plants, such as siderophores and antibiotics. Induced systemic resistance (ISR) in plants resembles pathogen-induced systemic acquired resistance (SAR) under conditions where the inducing bacteria and the challenging pathogen remain spatially separated. Both types of induced resistance render uninfected plant parts more resistant to pathogens in several plant species. Rhizobacteria induce resistance through the salicylic acid-dependent SAR pathway, or require jasmonic acid and ethylene perception from the plant for ISR. Rhizobacteria belonging to the genera Pseudomonas and Bacillus are well known for their antagonistic effects and their ability to trigger ISR. Resistance-inducing and antagonistic rhizobacteria might be useful in formulating new inoculants with combinations of different mechanisms of action, leading to a more efficient use for biocontrol strategies to improve cropping systems.
Background and Aims This study was aimed at assessing the diversity of putatively diazotrophic rhizobacteria associated with sunflower (Helianthus annuus L.) cropped in the south of Brazil, and to ...examine key plant growth promotion (PGP) characteristics of the isolates for the purposes of increasing plant productivity. 299 strains were isolated from the roots and rhizosphere of sunflower cultivated in five different areas using N-free media. 16S rDNA PCR-RFLP and 16S rRNA partial sequencing were used for identification and the Shannon index was used to evaluate bacterial diversity. Production of siderophores and indolic compounds (ICs), as well phosphate solubilization activities of each isolate were also evaluated in vitro. On the basis of multiple PGP activities, eight isolates were selected and tested for their N-fixation ability, and their capacity as potential PGPR on sunflower plants was also assessed. Results All except three Gram-positive strains (phylum Actinobacteria) belonged to the Gram-negative Proteobacteria subgroups Gamma (167), Beta (78), and Alpha (50) and the family Flavobacteriaceae (1). Shannon indexes ranged from 0.96 to 2.13 between the five sampling sites. Enterobacter and Burkholderia were the predominant genera isolated from roots and rhizosphere, respectively. Producers of siderophores and ICs were widely found amongst the isolates, but only 19.8% of them solubilized phosphate. About 8% of the isolates exhibited all three PGP traits, and these mostly belonged to the genus Burkholderia. Four isolates were able to stimulate the growth of sunflower plants under gnotobiotic conditions. Conclusions Enterobacter and Burkholderia were the dominant rhizospheric bacterial genera associated with sunflower plants. Inoculation with isolates belonging to the genera Achromobacter, Chryseobacterium, Azospirillum, and Burkholderia had a stimulatory effect on plant growth.
► There is a diverse population of PGPR in the rhizosphere, roots and stem of sugarcane. ► Achromobacter, Agrobacterium, Burkholderia, Gluconacetobacter, and Stenotrophomonas were the most abundant ...genera. ► A particular organism can promote plant growth by more than one mechanism. ► Gluconacetobacter diazotrophicus VI27 isolate was able to increase sugarcane yield.
Plant growth promoting (PGP) bacteria associated with sugarcane are a promising alternative for the expansion of this crop in Southern Brazil. In this study bacterial strains from different sugarcane fields were isolated to estimate their diversity, to evaluate some of their PGP activities and to use them as inoculant strains in field experiment. Samples of rhizospheric soil, roots, and stems of sugarcane were collected in six Rio Grande do Sul localities. The isolation of bacteria was made in three different N-free media. DNA from each isolate was subjected to nifH or 16S rDNA PCR-RFLP, and to the 16S rDNA partial sequencing. Five hundred and sixteen strains were isolated and several PGP characteristics were analyzed. Shannon index was used to evaluate the bacterial diversity. Indexes varying from 0.94 to 2.46 were obtained. Soil pH and clay were the characteristics most closely related to bacterial diversity. Achromobacter, Agrobacterium, Burkholderia, Gluconacetobacter, and Stenotrophomonas were the most abundant genera. Concerning the PGP activities, indolic compounds production was detected in 368 isolates; 138 isolates were able to solubilize phosphate; and 390 were siderophores producers. The inoculation of sugarcane with Gluconacetobacter diazotrophicus VI27 strain showed a significant increase in the number of sets germinated, in the amount of soluble solids, and in the yield of sugarcane juice compared with the control. As a conclusion, a diverse population of PGP bacteria was found in the sugarcane samples. These bacteria, especially G. diazotrophicus strain VI27, could be used as biofertilizers of sugarcane as well as other cereal crops under controlled conditions to avoid or reduce the use of standard N fertilizers.
The Estância Velha stream integrates the Sinos River Basin that provides drinking water in one of the most important Brazilian centers, the “Capital of tanneries,” and it receives effluents from ...tannery industries. In Brazil, water quality is monitored only through physicochemical and microbiological parameters, and considering the biomarkers’ importance in complementing the analysis, the present study was aimed at evaluating the environmental quality of the Estância Velha stream also through cytogenotoxic criteria, at the stream source (site 1), as well as upstream (site 2) and downstream (site 3) of the demographically most dense area. The results for dissolved oxygen, color, total phosphorus, silver, and thermotolerant coliforms classified the Estância Velha stream as class 4 in general; that is, the water is suitable only for navigation and to landscape harmony. Overall, the water was classified as poor by Water Quality Index (WQI) and as hypereutrophic by Trophic State Index (TSI). The main genotoxic alterations (micronuclei and nuclear buds) were observed in site 2, in which were obtained the highest levels of aluminum, silver, iron, and manganese. Despite this, most of the effluents released from the region are not treated prior to being discharged into the stream, suggesting the requirement for effluent treatment to ensure the quality of the water source available.
Taxonomic decisions within the order
have relied heavily on the interpretations of highly conserved 16S rRNA sequences and DNA-DNA hybridizations (DDH). Currently, bacterial species are defined as ...including strains that present 95-96% of average nucleotide identity (ANI) and 70% of digital DDH (dDDH). Thus, ANI values from 520 genome sequences of type strains from species of
order were computed. From the resulting 270,400 comparisons, a ≥95% cut-off was used to extract high identity genome clusters through enumerating maximal cliques. Coupling this graph-based approach with dDDH from clusters of interest, it was found that: (i) there are synonymy between
and
,
and
, "
," and
,
, and
,
, and
,
, and
, and
and
; (ii)
is not a synonym of
; (iii) "
" subsp.
and "
" subsp.
represent members of different species; (iv) the genome accessions GCF_003024615.1 ("
LMG 6,125
"), GCF_003024595.1 ("
LMG 11,892
"), GCF_003096615.1 ("
DSM 760
"), and GCF_000373025.1 ("
R-602 sp
") are not from the genuine type strains used for the respective species descriptions; and v) "
" Py2 and "
" KCTC 2,477
represent cases of misuse of the term "type strain".
comb. nov. and the reclassification of
as
is also proposed. To facilitate the downstream analysis of large ANI matrices, we introduce here ProKlust ("Prokaryotic Clusters"), an R package that uses a graph-based approach to obtain, filter, and visualize clusters on identity/similarity matrices, with settable cut-off points and the possibility of multiple matrices entries.
The potential of indigenously isolated bacteria from the Estância Velha stream to reduce Cr(VI) was evaluated and also the chromium contamination over the past ten years was verified in one of the ...most important industrial centers of Brazil, the “Brazilian Capital of Tanneries,” Estância Velha municipality in the Rio Grande do Sul State, South Brazil. Samples were collected from the Estância Velha stream at the source (P1), as well as at upstream (P2) and downstream (P3) of the most demographically area. The bacterial strains reduced between 52.5 and 61.6% of 250 mg L
–1
Cr(VI) in 48 h. The genus
Acinetobacter
was the most abundant and could efficiently reduce 500 mg L
–1
of Cr(VI); for example, P2.8 and P2.9 strains of
Acinetobacter ursingii
reduced 21.3 and 24.5% of 500 mg L
–1
of Cr(VI), respectively, after 48 h. Moreover, an analysis of Cr levels in the stream sediment reported up to 3594 mg. L
–1
of total Cr and up to 138 mg. L
–1
of Cr(VI) in 2009.
Acinetobacter
strains were identified as the most abundant and efficient in reducing Cr(VI), makes them an ideal candidate for cleaning environments contaminated with tannery effluents, an approach that is more cost-effective than the traditional methods.
Although inoculating soybean with rhizobia for biological nitrogen fixation is a common practice in agriculture, rhizobia are also known to associate with grasses. In this study, we evaluate the ...potential utility of the rhizobial strains SEMIA 587 and 5019 (
Bradyrhizobium elkanii
), 5079 (
Bradyrhizobium japonicum
), and 5080 (
Bradyrhizobium diazoefficiens
), recommended for Brazilian soybean inoculation, in colonizing black oat plants and promoting growth in black and white oats, and ryegrass. Inoculation of white oats with SEMIA 587 increase the seed germination (SG) by 32.09%, whereas the SG of black oats inoculated with SEMIA 587 and 5019 increased by 40.38% and 37.85%, respectively. Similarly, inoculation of ryegrass with all strains increased SG values between 24.63 and 27.59%. In addition, white oats with SEMIA 587 and 5080 had root areas significantly superior to those in other treatments, whereas inoculation with SEMIA 5079 and 5080 resulted in the highest volume of roots. Likewise, SEMIA 5079 and 5080 significantly increased the length, volume, and area of black oats roots, whereas SEMIA 587 increased the volume, area, and dry mass of roots and shoot. Inoculation in ryegrass with SEMIA 587 significantly increased the root volume. Moreover, most strains transformed with
gfp
and
gus
were observed to colonize the roots of black oats. Collectively, the findings of this study indicate that rhizobial strains recommended for inoculation of soybean can also be used to promote the growth of the three assessed grass species, and are able to colonize the roots of black oats.
Several strains of bacilli, mainly species of the genera
Bacillus and
Paenibacillus, displaying important plant growth promoting (PGP) characteristics were isolated from seven distinct rice ...production zones of the Rio Grande do Sul State, Brazil. Of 296 isolates, 155 were from rhizospheric soil and 141 from bulk soil. In order to evaluate the diversity among the isolates of each bacterial population the Shannon index was used on a 70% similarity basis. Diversity indices varying from 2.27 to 5.51 were obtained. Using principal coordinate analysis (PCA) to correlate bacterial diversity with soil parameters, it was found that soil pH was the characteristic most closely related to bacilli diversity. The bacilli isolated were also analyzed for some PGP activities. Of those 296 isolates, 94 and 148 produced between 0.1 and 30
μg of indole-3-acetic acid (IAA)
ml
−1
in vitro after 72 and 144
h of incubation, respectively. Twenty-two isolates were able to solubilize phosphate and 32 isolates produced siderophores.
Paenibacillus and
Bacillus genera were the most prominent groups in the rhizosphere and soil populations analyzed.
Paenibacillus borealis was the most frequent species in both locations. The isolate SVPR30, identified by 16S rRNA gene sequence analysis as a strain of
Bacillus sp., was chosen for
in vivo greenhouse experiments and proved to be very efficient in promoting a significant increase in the roots and shoot parts of rice plants. The identification and isolation of PGP bacilli from temperate and subtropical soils, which combine the ability to fix nitrogen with the production of substances capable to promote the plant growth, could significantly increase productivity of grain crops in Brazil.
Black wattle (
Acacia mearnsii
) is a forest species of significant economic importance in southern Brazil; as a legume, it forms symbiotic associations with rhizobia, fixing atmospheric nitrogen. ...Nonetheless, little is known about native rhizobia in soils where the species is cultivated. Therefore, this study aimed to evaluate the diversity and symbiotic efficiency of rhizobia nodulating
A. mearnsii
in commercial planting areas and validate the efficiency of a potential strain in promoting seedling development. To this end, nodules were collected from four
A. mearnsii
commercial plantations located in Rio Grande do Sul State, southern Brazil. A total of 80 rhizobia isolates were obtained from black wattle nodules, and thirteen clusters were obtained by rep-PCR. Higher genetic diversity was found within the rhizobial populations from the Duas Figueiras (H′ = 2.224) and Seival (H′ = 2.112) plantations. Twelve isolates were evaluated belonging to the genus
Bradyrhizobium,
especially to the species
Bradyrhizobium guangdongense.
The principal component analysis indicated an association between rhizobia diversity and the content of clay, Ca, Mg, and K. Isolates and reference strains (SEMIA 6163 and 6164) induced nodulation and fixed N via symbiosis with black wattle plants after 60 days of germination. The isolates DF2.4, DF2.3, DF3.3, SEMIA 6164, SEMIA 6163, CA4.3, OV3.4, and OV1.4 showed shoot nitrogen accumulation values similar to the N + control treatment. In the second experiment (under nursery conditions), inoculation with the reference strain SEMIA 6164 generally improved the growth of
A. mearnsii
seedlings, reinforcing its efficiency even under production conditions.
The bacterial strains SEMIA 587 and 5019 (
Bradyrhizobium elkanii
), 5079 (
Bradyrhizobium japonicum
), and 5080 (
Bradyrhizobium diazoefficiens
) are recommended for soybean inoculants in Brazil. In ...several countries, the current regulations are insufficient to induce companies for improving the quality of their products, leading to low performance and subsequent abandonment of inoculant use. From 2010 to 2014, 1086 samples coming mainly from Argentina and the southern region of Brazil were analyzed for viable cells counting, strains identification, and purity analysis according to the SDA/MAPA no. 30/2010 Normative Instruction. Most products were imported and formulated in liquid carriers with 5.0 × 10
9
colony-forming units (CFU)/mL. The strains most frequently used were SEMIA 5079/5080. Only 2.21% of samples had contaminants. The guaranteed concentration of viable cells in inoculants mostly ranged from 4.1 × 10
9
to 5.0 × 10
9
CFU/mL or CFU/g. The most frequently found concentration was above 1.1 × 10
10
CFU/mL or CFU/g, which was higher than the product guarantee. The inoculants used for soybean crop in Brazil have excellent quality, leading the country to the leadership in taking advantage of the biological nitrogen fixation benefits for a productive and sustainable agriculture.
PDF
