Sugarcane Rhizosphere Research Articles

Mycorrhizal diversity in the rhizosphere of sugarcane and grass on different soil types

Mycorrhiza has been known well as beneficial microbiota for supporting plant growth and production. Understanding of the variability and the consistency of the mycorrhizal diversity on various habitats is important for developing mycorrhizal utilization. Mycorrhizal diversity in the rhizosphere of sugarcane from 4 (four) soil types and the rhizosphere of grass from 3 (three) soil types were investigated in the present study. The results showed that Glomus indicated as a versatile genus because it was found as a common and dominant genus in the sugarcane rhizosphere on all of four soil types (Alfisol, Andisol, Inceptisol, Vertisol) and in the grass rhizosphere on all of three soil types (Ultisol, Oxisol, Histosol). In addition, Acaulospora was found as a common genus in grass rhizosphere. Statistical analysis indicated that P availability in the rhizosphere of sugarcane had a significantly negative correlation with mycorrhizal spore density, in which decreasing P availability significantly related with increasing spore density.

Assessment of two carrier materials for phosphate solubilizing biofertilizers and their effect on growth of wheat (Triticum aestivum L.)

Biofertilizers are usually carrier-based inoculants containing beneficial microorganisms. Incorporation of microorganisms in carrier material enables easy-handling, long-term storage and high effectiveness of biofertilizers. Objective of the present study was to assess enriched biogas sludge and soil as biofertilizer carriers on growth and yield of wheat. Six phosphate solubilizing strains were used in this study. Three phosphate solubilizing strains, 77-NS2 (Bacillus endophyticus), 77-CS-S1 (Bacillus sphaericus) and 77-NS5 (Enterobacter aerogenes) were isolated from the rhizosphere of sugarcane, two strains, PSB5 (Bacillus safensis) and PSB12 (Bacillus megaterium) from the rhizosphere of wheat and one halophilic phosphate solubilizing strain AT2RP3 (Virgibacillus sp.) from the rhizosphere of Atriplex amnicola, were used as bioinoculants. Phosphate solubilization ability of these strains was checked in vitro in Pikovskaya medium, containing rock phosphate (RP) as insoluble P source, individually supplemented with three different carbon sources, i.e., glucose, sucrose and maltose. Maximum phosphate solubilization; 305.6μg/ml, 217.2μg/ml and 148.1μg/ml was observed in Bacillus strain PSB12 in Pikovskaya medium containing sucrose, maltose and glucose respectively. A field experiment and pot experiments in climate control room were conducted to study the effects of biogas sludge and enriched soil based phosphorous biofertilizers on growth of wheat. Bacillus strain PSB12 significantly increased root and shoot dry weights and lengths using biogas sludge as carrier material in climate control room experiments. While in field conditions, significant increase in root and shoot dry weights, lengths and seed weights was seen by PSB12 and PSB5 (Bacillus) and Enterobacter strain 77-NS5 using biogas sludge as carrier. PSB12 also significantly increased both root and shoot dry weights and lengths in field conditions when used as enriched soil based inoculum. These results indicated that bacterial isolates having plant beneficial traits such as P solubilization are more promising candidates as biofertilizer when used with carrier materials.

Changes of bacterial communities in the rhizosphere of sugarcane under elevated concentration of atmospheric CO2

AbstractIt is believed that climate change will influence most of interactions that sustain life on Earth. Among these, the recruitment exerted by plants in their roots vicinity can change, leading to differential assemblages of microbiomes in the rhizosphere. We approached this issue analyzing the variations in the composition of bacterial communities in the rhizosphere of sugarcane cultivated under two concentrations of atmospheric CO2 (350 or 700 ppm). In addition to the analysis of bacterial community, the use of DNA‐SIP allowed the comparison of bacterial groups assimilating roots exudates (based on 13C‐labeled DNA) in both conditions, in a period of 8 days after the CO2 pulse. The separation of 13C‐DNA indicated the low but increasing frequency of labeling in the rhizosphere, as averages of 0.6, 2.4 and 5.0% of total DNA were labeled after 2, 4, and 8 days after the 13CO2 pulse, respectively. Based on large‐scale sequencing of the V6 region in the gene 16S rRNA, we found an increase in the bacterial diversity in the 13C‐DNA along the sampling period. We also describe the occurrence of distinct bacterial groups assimilating roots exudates from sugarcane cultivated under each CO2 concentration. Bacilli, Gammaproteobacteria, and Clostridia showed high affinity for the C‐sources released by sugarcane under 350 ppm of CO2, while under elevated concentration of CO2, the assimilation of roots exudates was prevalently made by members of Bacilli and Betaproteobacteria. The communities became more similar along time (4 and 8 days after CO2 pulse), in both concentrations of CO2, electing Actinobacteria, Sphingobacteriia, and Alphaproteobacteria as the major cross‐feeders on sugarcane exudates. In summary, we described the bacterial groups with higher affinity to assimilate roots exudates in the rhizosphere of sugarcane, and also demonstrated that the rhizosphere community can be differentially assembled in a future scenario with increased contents of CO2.

Genetic Diversity of Nitrogen-Fixing and Plant Growth Promoting Pseudomonas Species Isolated from Sugarcane Rhizosphere.

The study was designed to isolate and characterize Pseudomonas spp. from sugarcane rhizosphere, and to evaluate their plant- growth- promoting (PGP) traits and nitrogenase activity. A biological nitrogen-fixing microbe has great potential to replace chemical fertilizers and be used as a targeted biofertilizer in a plant. A total of 100 isolates from sugarcane rhizosphere, belonging to different species, were isolated; from these, 30 isolates were selected on the basis of preliminary screening, for in vitro antagonistic activities against sugarcane pathogens and for various PGP traits, as well as nitrogenase activity. The production of IAA varied from 312.07 to 13.12 μg mL−1 in tryptophan supplemented medium, with higher production in AN15 and lower in CN20 strain. The estimation of ACC deaminase activity, strains CY4 and BA2 produced maximum and minimum activity of 77.0 and 15.13 μmoL mg−1 h−1. For nitrogenase activity among the studied strains, CoA6 fixed higher and AY1 fixed lower in amounts (108.30 and 6.16 μmoL C2H2 h−1 mL−1). All the strains were identified on the basis of 16S rRNA gene sequencing, and the phylogenetic diversity of the strains was analyzed. The results identified all strains as being similar to Pseudomonas spp. Polymerase chain reaction (PCR) amplification of nifH and antibiotic genes was suggestive that the amplified strains had the capability to fix nitrogen and possessed biocontrol activities. Genotypic comparisons of the strains were determined by BOX, ERIC, and REP PCR profile analysis. Out of all the screened isolates, CY4 (Pseudomonas koreensis) and CN11 (Pseudomonas entomophila) showed the most prominent PGP traits, as well as nitrogenase activity. Therefore, only these two strains were selected for further studies; Biolog profiling; colonization through green fluorescent protein (GFP)-tagged bacteria; and nifH gene expression using quantitative real-time polymerase chain reaction (qRT-PCR) analysis. The Biolog phenotypic profiling, which comprised utilization of C and N sources, and tolerance to osmolytes and pH, revealed the metabolic versatility of the selected strains. The colonization ability of the selected strains was evaluated by genetically tagging them with a constitutively expressing GFP-pPROBE-pTetr-OT plasmid. qRT-PCR results showed that both strains had the ability to express the nifH gene at 90 and 120 days, as compared to a control, in both sugarcane varieties GT11 and GXB9. Therefore, our isolated strains, P. koreensis and P. entomophila may be used as inoculums or in biofertilizer production for enhancing growth and nutrients, as well as for improving nitrogen levels, in sugarcane and other crops. The present study, to the best of our knowledge, is the first report on the diversity of Pseudomonas spp. associated with sugarcane in Guangxi, China.

Isolation, characterization and inter-relationship of phosphate solubilizing bacteria from the rhizosphere of sugarcane and rice

Abstract Phosphate solubilizing bacteria (PSB) have the ability to solubilize insoluble phosphorus to make it available for plant roots to be absorbed. In this study, isolation of rhizobacteria and screening of their ability for phosphate solubilization, production of indole acetic acid (IAA), antagonistic activity against fungal pathogen and intrinsic antibiotic resistance was studied. In total, 15 isolates of PSB were found gram negative with rod shaped cells. Different levels of antibiotic resistance was seen against four antibiotics (Ampicillin, Kanamycin, Tetracycline and Streptomycin 25, 30, 30 and 10 μg/ml respectively) by Rhizobacterial isolates (Seven isolates were found to show antifungal activity against Fusarium oxysporum). All PSB isolates were found to solubilize insoluble phosphorous Ca3(PO4) and produce IAA. Two PSB isolates sequences were found novel and were submitted in NCBI database. Conclusively, combine application of rhizobacterial isolates, Sugarcane (SC-22) in addition with antifungal agent can prove to be an excellent combination to solubilize insoluble phosphorus and to act as antifungal remedy. Further this combination can be eco-friendly and prove to be cost effective strategy to improve crop production.

Evaluating the growth performance of Two <i>Azotobactor</i> spp. In liquid glucose broth and tryptic peptone broth as inoculum for the production of bio-fertilizers

Biofertilizers with Azotobacter spp. releases available nitrogen to the plant rhizosphere. A media that yield a high viable inoculum cell count in a shorter incubation period is important for commercial production of biofertilizers. Current study evaluates the growth performances of Azotobacter chroococcum and Azotobacter vinelandii, two spp. commonly found in sugarcane rhizosphere, in two broth cultures: tryptic peptone broth (TPB) and liquid glucose broth (LGB) using optical density (OD) measurements at a wavelength of 620 nm over an incubation period of 12 - 15 hours. The analysis of variance revealed significant (p<0.001) species, broth and species × broth interaction on OD. Azotobacter spp. had a higher growth rate in the protein enriched TPB compared to LGB. Azotobacter chroococcum had a higher growth rate than A. vinelandii particularly in TPB. Despite the cost, A. chroococcum inoculum grown in TPB can be recommended for commercial biofertilizer production, due to yield and time advantage.

Bacterial Abilities and Adaptation Toward the Rhizosphere Colonization.

The rhizosphere harbors one of the most complex, diverse, and active plant-associated microbial communities. This community can be recruited by the plant host to either supply it with nutrients or to help in the survival under stressful conditions. Although selection for the rhizosphere community is evident, the specific bacterial traits that make them able to colonize this environment are still poorly understood. Thus, here we used a combination of community level physiological profile (CLPP) analysis and 16S rRNA gene quantification and sequencing (coupled with in silico analysis and metagenome prediction), to get insights on bacterial features and processes involved in rhizosphere colonization of sugarcane. CLPP revealed a higher metabolic activity in the rhizosphere compared to bulk soil, and suggested that D-galacturonic acid plays a role in bacterial selection by the plant roots (supported by results of metagenome prediction). Quantification of the 16S rRNA gene confirmed the higher abundance of bacteria in the rhizosphere. Sequence analysis showed that of the 252 classified families sampled, 24 were significantly more abundant in the bulk soil and 29 were more abundant in the rhizosphere. Furthermore, metagenomes predicted from the 16S rRNA gene sequences revealed a significant higher abundance of predicted genes associated with biofilm formation and with horizontal gene transfer (HGT) processes. In sum, this study identified major bacterial groups and their potential abilities to occupy the sugarcane rhizosphere, and indicated that polygalacturonase activity and HGT events may be important features for rhizosphere colonization.

Burkholderia tropica UNA BACTERIA CON GRAN POTENCIAL PARA SU USO EN LA AGRICULTURA

The genus Burkholderia whit over 90 species reported to date, is divided into two major groups phylogenetically distant. The first group is made up of pathogenic species which highlights referred opportunistic pathogens such as Burkholderia cepacia (Bcc) complex; The other group consists of nonpathogenic species with skills to promote plant growth and rhizoremediation. Burkholderia tropica is a bacterium capable of fixing nitrogen; isolated from the rhizosphere, rhizoplane, stem and roots of corn plants and sugarcane. Besides its ability diazotrofa, B. tropica presents characteristics that classify it as a plant promoter bacteria, such growth as is the ability to produce siderophores, solubilizing phosphates, producing exo-heteropolysaccharides, and can be used as biocontrol for some plant parasites, which It makes it a promising bacteria to be used in the agricultural sector.

Observations on Hoplolaimus indicus Sher, 1963 and Hoplolaimus seinhorsti Luc, 1958 (Nematoda: Hoplolaimidae) from Southern Iran

Morphological observations are made on several populations of Hoplolaimus indicus and Hoplolaimus seinhorsti, recovered from rhizosphere of mango, tamarind, sour orange and sugarcane from the southern regions of Iran. Detailed studies on the two species Hoplolaimus dubius and H. indicus being separated from each other based on some morphological characters, revealed each of them having intra-specific and overlapping variations in morphology and morphometric ranges, enough for not separating two closely related aforementioned species and as a result, H. dubius is considered as a junior synonym of H. indicus. Observations on H. seinhorsti also supported the Siddiqi's decision on the synonymy of Hoplolaimus sheri with H. seinhorsti. The results of the phylogenetic analyses using D2-D3 expansion segments of 28S rRNA gene were in agreement with the results of previous works, i.e. the classic scheme for assigning species of the genus into two ancestral and/or derived groups was supported. In phylogenetic trees inferred, using different analysis methods, the Iranian populations of H. indicus were located in the same clade with H. seinhorsti and H. columbus, belonging to derived group of species of the genus characterized by having six nuclei in pharyngeal glands, less than four incisures at each lateral field and anteriorly situated position of excretory pore to hemizonid.

Intercropping in Sugarcane Cultivation Influenced the Soil Properties and Enhanced the Diversity of Vital Diazotrophic Bacteria

Soil survey was conducted at four different locations of Guangxi, China to investigate the effect of peanut and soybean inter-cropping in sugarcane cultivation on the soil properties and diazotrophic bacterial diversity. Principal component analysis result shown (PCA) showed difference impact of intercropping and monoculture on the basis of biological and chemical properties of soil. Two-way analysis of variance of soil properties showed a significant interactive effect with locations and cultivation systems. Microbial enumeration results demonstrated that intercropping system enhanced the diazotrophic population. After isolation of diazotrophs, 21 selected bacteria were characterized by siderophore, phosphate, indole acetic acid, 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase and nitrogenase assay. Among the identified bacteria, isolate MYSP104 showed maximum nitrogenase activity and isolate MYSS78 showed maximum ACC deaminase activity. Partial 16S rRNA gene sequencing results classified these diazotrophs in six phyla (Firmicutes, α, β, Υ-proteobacteria, actinobacteria and bacteroidetes). Diazotrophs such as Bacillus tequilensis, Variovorax paradoxus, Acidovorax facilis, Leucobacter aridicollis, Streptomyces fimicarius and Pseudomonas nitroreducens were reported for the first time from the sugarcane rhizosphere of Guangxi, China. Venn diagram explained that seven bacterial species (Brevibacterium, Burkholderia, Delftia, Leucobacter, Pseudomonas, Sinorhizobium and Variovorax) were recognized with soybean and sugarcane intercropping cultivation systems. This study concluded that intercropping system could enhance the population of N-fixers in soil. Soybean intercropping influenced the soil chemical and biological properties better than peanut. Moreover, the isolated diazotrophs need further characterization and they might be utilized as bio-inoculums for commercial sugarcane production in the future.

Solubilization of Potassium Containing Mineral by Microorganisms From Sugarcane Rhizosphere

Abstract Potassium solubilizing microorganisms (KSM) isolated from sugarcane rhizosphere and their capability on solubilization from some insoluble potassium were examined. Isolation of potassium solubilizer was carried out from three sugarcane plantations area, on Alexandrov's agar medium. From the 41 isolated microorganisms were selected 15 isolates potassium solubilizing microorganisms which exhibiting highest potassium solubilization (solubility index) on solid medium. All the KSM were found to be capable of solubilizing K from insoluble K-bearing minerals source, and the solubilization zone ranging from 0.15 to 4.5 cm. 13.3% isolate has Solubility Index (SI) more than four on solid medium. Quantitative test result of KSM conducted on liquid medium containing potassium mineral trachyte, feldspar, leucite (Pati and Situbondo), released water soluble-K (exchangeable-K) ranging from 0.13 to 12.25 mg.L−1 (Feldspar); 1.24 to 15.57 mg L−1 (Leucite pati); 1.01 to 4.,59 mg L−1 (Leucite Situbondo); and 0.16 to 6,34 mg L−1 (Trachyte). KSM strain Sbr3 caused maximum solubilization on feldspar (12.25 mg L−1), KSM strain Asb3 on leucite Pati (18.17 mg L−1), KSM strain Prj3 on leucite Situbondo (16.14 mg L−1), whereas KSM strain Prj5 caused maximum solubilization on trachyte (6.92 mg L−1). All isolates produced organic acid citric, ferulic and coumaric, some isolates also produced malic and syringic acid. Total organic acid produced by isolated ranging from 130.42 to 434.44 mg.L−1. Ferulic acid was produced by all isolates on all of K sources higher than other organic acid.

Verrucomicrobial community structure and abundance as indicators for changes in chemical factors linked to soil fertility.

Here we show that verrucomicrobial community structure and abundance are extremely sensitive to changes in chemical factors linked to soil fertility. Terminal restriction fragment length polymorphism fingerprint and real-time quantitative PCR assay were used to analyze changes in verrucomicrobial communities associated with contrasting soil nutrient conditions in tropical regions. In case study Model I (“Slash-and-burn deforestation”) the verrucomicrobial community structures revealed disparate patterns in nutrient-enriched soils after slash-and-burn deforestation and natural nutrient-poor soils under an adjacent primary forest in the Amazonia (R = 0.819, P = 0.002). The relative proportion of Verrucomicrobia declined in response to increased soil fertility after slash-and-burn deforestation, accounting on average, for 4 and 2 % of the total bacterial signal, in natural nutrient-poor forest soils and nutrient-enriched deforested soils, respectively. In case study Model II (“Management practices for sugarcane”) disparate patterns were revealed in sugarcane rhizosphere sampled on optimal and deficient soil fertility for sugarcane (R = 0.786, P = 0.002). Verrucomicrobial community abundance in sugarcane rhizosphere was negatively correlated with soil fertility, accounting for 2 and 5 % of the total bacterial signal, under optimal and deficient soil fertility conditions for sugarcane, respectively. In nutrient-enriched soils, verrucomicrobial community structures were related to soil factors linked to soil fertility, such as total nitrogen, phosphorus, potassium and sum of bases, i.e., the sum of calcium, magnesium and potassium contents. We conclude that community structure and abundance represent important ecological aspects in soil verrucomicrobial communities for tracking the changes in chemical factors linked to soil fertility under tropical environmental conditions.Electronic supplementary materialThe online version of this article (doi:10.1007/s10482-015-0530-3) contains supplementary material, which is available to authorized users.

Nitrogen fertilizer dose alters fungal communities in sugarcane soil and rhizosphere.

Fungi play important roles as decomposers, plant symbionts and pathogens in soils. The structure of fungal communities in the rhizosphere is the result of complex interactions among selection factors that may favour beneficial or detrimental relationships. Using culture-independent fungal community profiling, we have investigated the effects of nitrogen fertilizer dosage on fungal communities in soil and rhizosphere of field-grown sugarcane. The results show that the concentration of nitrogen fertilizer strongly modifies the composition but not the taxon richness of fungal communities in soil and rhizosphere. Increased nitrogen fertilizer dosage has a potential negative impact on carbon cycling in soil and promotes fungal genera with known pathogenic traits, uncovering a negative effect of intensive fertilization.

Characterization of Plant Growth Promoting Bacteria from Sugarcane (Saccharum officinarum L.) Rhizosphere of Wonji-Shoa Sugar Estate and Farmers Landraces of Ethiopia

Characterization of Plant Growth Promoting Bacteria from Sugarcane (Saccharum officinarum L.) Rhizosphere of Wonji-Shoa Sugar Estate and Farmers Landraces of Ethiopia

Bacillus-related Spore Formers: Attractive Agents for Plant Growth Promotion.

Bacillus-related Spore Formers: Attractive Agents for Plant Growth Promotion.

Isolation and Identification of Rhizospheric Bacteria in Sugarcane (Saccharum spp. L.) Cultivated on Acrisols and Ferrasols of Dong Nai Province, the Southeast of Vietnam

Nitrogen-fixing and phosphate-solubilizing bacterial diversity and population dynamics in the Acrisol and Ferrasol rhizosphere of sugarcane grown in Dong Nai province, the eastern of South Vietnam was studied. Soil rhizosphere samples were taken in three districts (sites) of this region. Physical and chemical characteristics of soil samples and total nitrogen-fixing and phosphate-solubilizing bacteria counts were determined by drop plate count method together with 16S rRNA gene fragments amplified from DNA using eubacterial universal primers (27F and 1492R). A total of 31 isolates were isolated on two media (Burk’s N-free and NBRIP) and all of them have ability of nitrogen fixation and phosphate solubilization together with IAA biosynthesis. Population of nitrogen-fixing and phosphate-solubilizing bacteria correlated with N total concentration and organic matter content in soil closely (P<0.05). The sequences from selected nitrogen-fixing and phosphate-solubilizing bacteria (12 isolates) showed high degrees of similarity to those of the GenBank references strains (between 98% and 99%). From 12 isolates, 7 belonged to Bacilli, while 2 were Beta-Proteobacteria, 1 was Acidobacteria and 2 were Bacteroides. Based on Pi value (nucleotide diversity), Bacilli group had the highest theta value and Theta values (persequence) from S of SNP for DNA polymorphism were calculated for each group and Bacilli group had the highest values in comparison to three groups. From these results showed that two strains (Bacillus megaterium B6 (Ferrasols) and Sphingomonas sp. P14 (Acrisols)) revealed promising candidates with multiple beneficial characteristics and they have the potential for application as inoculants adapted to poor soils and sugarcane tree because they are not only famous strains but also are safety strains for agricultural sustainable.

Isolation and Characterization of Phosphate solubilising Burkholderia spp from the crops rhizosphere

It is an important trait in plant growth-promoting bacteria the ability to solubilize and mineralize insoluble inorganic phosphate compounds, making the element available for plants. High populations of phosphate solubilizing bacteria (PSB) will increases the P uptake by plants and reduce the application of organic fertilizers. In this study, a total of 14 PSB isolates from rhizosphere of maize, cotton, ragi, rice, turmeric, sugarcane, cowpea and green gram were tested for the mineral phosphate solubilizing (MPS) activities in Hydroxy Apatite (HAP) broth by analyzing the soluble-P content after 72 h of incubation at 30 0C. The ‘P’ solubilising ability of SGN 1 was found to be 35.56 mg/100ml isolated from sugarcane rhizosphere soil. SGN 1 which was showing higher phosphate solubilizing ability in HAP broth was selected for molecular characterization with amplifying and sequencing of 1.3 kb 16S rRNA gene. Based on the BLASTn homology it was found that PSB sugarcane isolate SGN1 having 95% identity with showed 99% homology with Burkholderia thailandensis.

Establishing monoxenic culture of arbuscular mycorrhizal fungus Glomus intraradices through root organ culture

Arbuscular mycorrhizal fungi are soil fungi distributed worldwide, forming symbiosis with most of the vascular plants for their growth and survival, which is used for sustainable agriculture and ecosystem management. This study investigated the establishment of monoxenic cultures of Glomus intraradices in association with transformed carrot hairy root. The G.intraradices spores were isolated from sugarcane rhizosphere by wet sieving and decanting technique and propagated in open pot culture. Transformation in to carrot hairy root was done using Agrobacterium rhizogenes. Surface sterilization of G.intraradices spores co-cultured with transformed carrot hairy root in Modified Strulla and Romand (MSR) medium was found the host root growth as well as for germination AM spores. After three months of incubation in dark condition, significant production of extensive hyphal growth on MSR medium and an average of 8500-9000 spores per petri dish was observed. The in vitro inoculum exhibited higher potential of root colonization due to numerous intraradices mycelium with extensive spore load. The produced monoxenic inoculum can be used in place of traditional system where it has a advantage of producing contaminant free propagulas. Thus the monoxenic culture system, a powerful tool, of AM sporulation, can be used for the mass production of monoxenic inoculum of AM fungi besides studying its biology.

Bacillus subtilis Isolated from Sugarcane Rhizosphere Produces PHA to Defend NaCl Induced Stress

Bacillus subtilis Isolated from Sugarcane Rhizosphere Produces PHA to Defend NaCl Induced Stress

Effects of intercropping with soybean on bacterial and nitrogen-fixing bacterial diversity in the rhizosphere of sugarcane

Aims In order to investigate the effects of intercropping with soybean on the diversities of bacteria and nitrogenfixing bacteria in the rhizosphere of sugarcane(Saccharum officinarum), to collect and exploit nitrogen-fixing bacterial resources, and to screen for efficient sugarcane-associative nitrogen fixation system, an experiment was conducted by cultivating three sugarcane cultivars ‘ROC22', ‘GT21', and ‘B8' with a soybean(Glycine max) cultivar ‘Guizao 2'. Methods Rhizospheric soil bacteria and nitrogen-fixing bacteria were measured in the rhizosphere of sugarcane intercropped with soybean by using a nested-PCR combined with denaturing gradient gel electrophoresis(DGGE) technique. The specific bacterial 16 S rRNA gene fragments and nitrogen-fixing bacteria nifH gene fragments were amplified for phylogenetic and diversity analyses. Important findings Cluster analysis of bacterial communities showed that the sugarcane-soybean intercropping changed the community composition of rhizospheric soil bacteria and nitrogen-fixing bacteria, with the effect being greater on nitrogen-fixing bacterial communities than on the soil bacterial communities. The intercropping system had a significant effect on the diversity of the rhizospheric bacteria and nitrogen-fixing bacteria; the impact on the diversity of nitrogen-fixing bacteria was greater than on the soil bacteria, and was only minor on the dominance of the bacterial species. Analyses of Shannon-Wiener index and Simpson index showed that thenitrogen-fixing bacteria differed in diversity among the treatments with different sugarcane varieties, and that the sugarcane cultivar ‘ROC22'-soybean intercropping had the greatest diversity. The diversity of soil bacteria in the rhizosphere of sugarcane varied greatly among different stages of crop growth; the booming stage of soybean had the greatest diversity and variations in the diversity among treatments in soil bacteria in the rhizosphere of sugarcane, and thereafter the two variables decreased. In conclusion, the sugarcane-soybean intercropping system had significant effects on the community structures and diversities of soil bacteria and nitrogen-fixing bacteria in the rhizosphere of sugarcane. This is of help for understanding the beneficial effects of sugarcane-soybean intercropping and for identifying efficient sugarcane-associative nitrogen fixation systems.