A novel method for sampling bacteria on plant root and soil surfaces at the microhabitat scale

This study reports the first method for sampling bacteria at a spatial scale approximating a microhabitat. At the core of this method is the use of tungsten rods with laser-cut tips of known surface area (0.013 mm(2)). Exposed plant root or soil surfaces were viewed with a dissecting microscope and micro-sampling rods were guided to sample sites using a micro-manipulator. Bacteria that adhered to the sampling tips were then recovered for microbiological analyses. The efficiency of this method for removing bacteria from root surfaces was similar to that with which bacteria are recovered from dissected root segments using the conventional technique of washing. However, as the surface area of the micro-sampling tips was known, the new method has the advantage of eliminating inaccuracy in estimates of bacterial densities due to inaccurate estimation of the root or soil surface sampled. When used to investigate spatial distributions of rhizoplane bacteria, the new technique revealed trends that were consistent with those reported with existing methods, while providing access to additional information about community structure at a much smaller spatial scale. The spatial scale of this new method is ca. 1000-times smaller than other sampling methods involving swabbing. This novel technique represents an important methodological step facilitating microbial ecological investigations at a microhabitat scale.     

Relationship between assemblages of mycorrhizal fungi and bacteria on grass roots

Soils support an enormous microbial diversity, but the ecological drivers of this diversity are poorly understood. Interactions between the roots of individual grass species and the arbuscular mycorrhizal (AM) fungi and bacteria in their rhizoplane were studied in a grazed, unimproved upland pasture. Individual root fragments were isolated from soil cores, DNA extracted and used to identify plant species and assess rhizoplane bacterial and AM fungal assemblages, by amplifying part of the small-subunit ribosomal RNA gene, followed by terminal restriction fragment length polymorphism analysis. For the first time we showed that AM fungal and bacterial assemblages are related in situ and that this relationship occurred at the community level. Principal coordinate analyses of the data show that the AM fungi were a major factor determining the bacterial assemblage on grass roots. We also report a strong influence of the composition of the plant community on AM fungal assemblage. The bacterial assemblage was also influenced by soil pH and was spatially structured, whereas AM fungi were influenced neither by the bacteria nor by soil pH. Our study shows that linkages between plant roots and their microbial communities exist in a complex web of interactions that act at individual and at community levels, with AM fungi influencing the bacterial assemblage, but not the other way round.     

西北黄土高原柠条种植区土壤微生物多样性分析

柠条锦鸡儿(Caragana korshinskii)是我国黄土高原区重要的饲用豆科灌木植物。为揭示土壤微生物与柠条种植之间的关系,采用未培养技术提取样品宏基因组DNA,分别构建柠条根表、根际和自然土16SrDNA文库,分析各文库微生物群落的变化。结果显示,随距离柠条根部渐远,微生物数量呈现递减趋势。聚类分析发现,变形杆菌纲是根表土壤区系中的优势微生物种群(70.3%),尤其存在大量α-Proteobacteria类的能诱使植物形成根瘤的根瘤菌和对植物有促生作用的γ-Proteobacteria类微生物;而在根际和自然土中,酸杆菌属(Acidobacteria)和古菌(Archaea)数量较多。柠条根际的多样性指数最高,而根表和自然土微生物类群具有较高的优势度,表现出从根表、根际植物相关微生物到自然土单一简单微生物类群的过渡。说明植物根系和土壤环境与微生物类群具有相互选择性。     

Microbial populations and activities in the rhizoplane of rock-weathering desert plants. I. Root colonization and weathering of igneous rocks

Dense layers of bacteria and fungi in the rhizoplane of three species of cactus (Pachycereus pringlei, Stenocereus thurberi, Opuntia cholla) and a wild fig tree (Ficus palmeri) growing in rocks devoid of soil were revealed by bright-field and fluorescence microscopy and field emission scanning electron microscopy. These desert plants are responsible for rock weathering in an ancient lava flow at La Purisima-San Isidro and in sedimentary rock in the Sierra de La Paz, both in Baja California Sur, Mexico. The dominant bacterial groups colonizing the rhizoplane were fluorescent pseudomonads and bacilli. Seven of these bacterial species were identified by the 16S rRNA molecular method. Unidentified fungal and actimomycete species were also present. Some of the root-colonizing microorganisms fixed in vitro N(2), produced volatile and non-volatile organic acids that subsequently reduced the pH of the rock medium in which the bacteria grew, and significantly dissolved insoluble phosphates, extrusive igneous rock, marble, and limestone. The bacteria were able to release significant amounts of useful minerals, such as P, K, Mg, Mn, Fe, Cu, and Zn from the rocks and were thermo-tolerant, halo-tolerant, and drought-tolerant. The microbial community survived in the rhizoplane of cacti during the annual 10-month dry season. This study indicates that rhizoplane bacteria on cacti roots in rock may be involved in chemical weathering in hot, subtropical deserts.     

Tomato genotype and Azospirillum inoculation modulate the changes in bacterial communities associated with roots and leaves

AIMS: To evaluate the effect of plant variety and Azospirillum brasilense inoculation on the microbial communities colonizing roots and leaves of tomato (Lycopersicon esculentum Mill.) plants. METHODS AND RESULTS: Seeds of cherry and fresh-market tomato were inoculated with A. brasilense BNM65. Sixty days after planting, plants were harvested and the microbial communities of the rhizoplane and phyllosphere were analysed by community-level physiological profiles (CLPP) using BIOLOG EcoPlates and denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S rRNA genes. Differences on the rhizoplane and phyllosphere bacterial communities between the two tomato types were detected by principal component analysis of the CLPP; DGGE fingerprints also showed differences at the phyllosphere level. Fresh-market tomato had a more complex phyllosphere bacterial community than cherry tomato, as determined by DGGE profiles. Physiological and genetic changes on phyllosphere and rhizoplane bacterial communities by Azospirillum seed inoculation were evident only on cherry tomato. CONCLUSIONS: Tomato genotype affects the response of native bacterial communities associated with the roots and leaves to A. brasilense seed inoculation. SIGNIFICANCE AND IMPACT OF THE STUDY: The successful implementation of Azospirillum inoculation requires not only the consideration of the interactions between A. brasilense strains and plant genotypes, but also the plant-associated microflora.     

Root-induced increases in soil pH and nutrient availability to field-grown cereals and legumes on acid sandy soils of Sudano-Sahelian West Africa

A field experiment with millet (Pennisetum glaucum L.), sorghum [Sorghum bicolor (L.) Moench], cowpea (Vigna unguiculata L.) and groundnut (Arachnis hypogeae L.) was conducted on severely P-deficient acid sandy soils of Niger, Mali and Burkina Faso to measure changes in pH and nutrient availability as affected by distance from the root surface and by mineral fertiliser application. Treatments included three rates of phosphorus (P) and four levels of nitrogen (N) application. Bulk, rhizosphere and rhizoplane soils were sampled at 35, 45 and 75 DAS in 1997 and at 55 and 65 DAS in 1998. Regardless of the cropping system and level of mineral fertiliser applied, soil pH consistently increased between 0.7 and two units from the bulk soil to the rhizoplane of millet. Similar pH gradients were observed in cowpea, but pH changes were much smaller in sorghum with a difference of only 0.3 units. Shifts in pH led to large increases in nutrient availability close to the roots. Compared with the bulk soil, available P in the rhizoplane was between 190 and 270% higher for P-Bray and between 360 and 600% higher for P-water. Exchangeable calcium (Ca) and magnesium (Mg) levels were also higher in the millet rhizoplane than in the bulk soil, whereas exchangeable aluminium (Al) levels decreased with increasing pH close to the root surface. The results suggest an important role of root-induced pH increases for crops to cope with acidity-induced nutrient deficiency and Al stress of soils in the Sudano-Sahelian zone of West Africa. This revised version was published online in June 2006 with corrections to the Cover Date.     

Isolation and identification of potential phosphate solubilizing bacteria from the rhizoplane of Oryza sativa L. cv. BR29 of Bangladesh

A total of 30 bacteria were isolated from the rhizoplane of rice cv. BR29 cultivated in Mymensingh, Bangladesh and from the seedlings obtained from surface-sterilized seeds of BR29. Upon screening, 6 isolates showed varying levels of phosphate solubilizing activity in both agar plate and broth assays using National Botanical Research Institute's phosphate medium. The bacterial isolates were identified based on their phenotypic and 16S rRNA genes sequencing data as Acinetobacter sp. BR-12, Klebsiella sp. BR-15, Acinetobacter sp. BR-25, Enterobacter sp. BR-26, Microbacterium sp. BRS-1 and Pseudomonas sp. BRS-2. The BR-25 exhibited highest phosphate solubilizing activity followed by BR-15. They grew rapidly in the liquid medium at pH 5 and 7 but almost no growth occurred at pH 3. The pH value of the culture medium was decreased with bacterial growth suggesting that they might secrete organic acids to solubilize insoluble phosphorus. Scanning electron microscope analysis of two-week-old rice seedlings germinated from seeds previously inoculated with BR-25 and BR-15 revealed dense colonization at the root surfaces presumably using fimbriae on the bacterial cells.     

Links between plant and rhizoplane bacterial communities in grassland soils, characterized using molecular techniques

Molecular analysis of grassland rhizosphere soil has demonstrated complex and diverse bacterial communities, with resultant difficulties in detecting links between plant and bacterial communities. These studies have, however, analyzed "bulk" rhizosphere soil, rather than rhizoplane communities, which interact most closely with plants through utilization of root exudates. The aim of this study was to test the hypothesis that plant species was a major driver for bacterial rhizoplane community composition on individual plant roots. DNA extracted from individual roots was used to determine plant identity, by analysis of the plastid tRNA leucine (trnL) UAA gene intron, and plant-related bacterial communities. Bacterial communities were characterized by analysis of PCR-amplified 16S rRNA genes using two fingerprinting methods: terminal restriction fragment length polymorphisms (T-RFLP) and denaturing gradient gel electrophoresis (DGGE). Links between plant and bacterial rhizoplane communities could not be detected by visual examination of T-RFLP patterns or DGGE banding profiles. Statistical analysis of fingerprint patterns did not reveal a relationship between bacterial community composition and plant species but did demonstrate an influence of plant community composition. The data also indicated that topography and other, uncharacterized, environmental factors are important in driving bacterial community composition in grassland soils. T-RFLP had greater potential resolving power than DGGE, but findings from the two methods were not significantly different.     

Root exudation and rhizoplane bacterial abundance of barley (Hordeum vulgare L.) in relation to nitrogen fertilization and root growth

The abundance of bacteria in the rhizoplane of barley varieties was investigated at different soil nitrogen levels. Increased amendments of nitrogen resulted in higher bacterial numbers in the rhizoplane of barley seedlings of different varieties. A negative correlation was found between nitrogen level in the soil and the growth rate of the seedling roots. The effect of nitrogen on the bacterial abundances could be indirect through changed root growth and thereby changed exudation. The exudation of soluble organic carbon componds from barley seedling roots were measured in hydroponic culture. The effect of natural variation in root growth rate and of different concentrations of nitrogen in the nutrient solution was investigated. The amount of exudates consituted 2–66% of the dry weight increase in root biomass, depending on the root growth. Slower growing roots released considerably more organic carbon per unit root weight than faster growing roots. The variation in root exudation appeared to be mainly explained by differences in root growth, rather than of the nitrogen concentration in the nutrient solution. A significantly higher exudation rate was found during day time compared to night.     

Diversity of root-associated bacteria associated with field-grown canola (Brassica napus L.) and wheat (Triticum aestivum L.)

Little is known about the composition and diversity of the bacterial community associated with plant roots. The purpose of this study was to investigate the diversity of bacteria associated with the roots of canola plants grown at three field locations in Saskatchewan, Canada. Over 300 rhizoplane and 220 endophytic bacteria were randomly selected from agar-solidified trypticase soy broth, and identified using fatty acid methyl ester (FAME) profiles. Based on FAME profiles, 18 bacterial genera were identified with a similarity index >0.3, but 73% of the identified isolates belonged to four genera: Bacillus (29%), Flavobacterium (12%), Micrococcus (20%) and Rathayibacter (12%). The endophytic community had a lower Shannon-Weaver diversity index (1.35) compared to the rhizoplane (2.15), and a higher proportion of Bacillus, Flavobacterium, Micrococcus and Rathayibacter genera compared to rhizoplane populations. Genera identified in the endophytic isolates were also found in the rhizoplane isolates. Furthermore, principal component analysis indicated three clusters of bacteria regardless of their site of origin, i.e., rhizoplane or endophytic. In addition, the rhizoplane communities of canola and wheat grown at the same site differed significantly. These results indicate that diverse groups of bacteria are associated with field-grown plants and that endophytes are a subset of the rhizoplane community.     

Links between Plant and Rhizoplane Bacterial Communities in Grassland Soils, Characterized Using Molecular Techniques

Molecular analysis of grassland rhizosphere soil has demonstrated complex and diverse bacterial communities, with resultant difficulties in detecting links between plant and bacterial communities. These studies have, however, analyzed “bulk” rhizosphere soil, rather than rhizoplane communities, which interact most closely with plants through utilization of root exudates. The aim of this study was to test the hypothesis that plant species was a major driver for bacterial rhizoplane community composition on individual plant roots. DNA extracted from individual roots was used to determine plant identity, by analysis of the plastid tRNA leucine (trnL) UAA gene intron, and plant-related bacterial communities. Bacterial communities were characterized by analysis of PCR-amplified 16S rRNA genes using two fingerprinting methods: terminal restriction fragment length polymorphisms (T-RFLP) and denaturing gradient gel electrophoresis (DGGE). Links between plant and bacterial rhizoplane communities could not be detected by visual examination of T-RFLP patterns or DGGE banding profiles. Statistical analysis of fingerprint patterns did not reveal a relationship between bacterial community composition and plant species but did demonstrate an influence of plant community composition. The data also indicated that topography and other, uncharacterized, environmental factors are important in driving bacterial community composition in grassland soils. T-RFLP had greater potential resolving power than DGGE, but findings from the two methods were not significantly different.     

Comparison of bacterial community structures in the rhizoplane of tomato plants grown in soils suppressive and conducive towards bacterial wilt.

It has been reported that the growth of Ralstonia solanacearum is suppressed at the rhizoplane of tomato plants and that tomato bacterial wilt is suppressed in plants grown in a soil (Mutsumi) in Japan. To evaluate the biological factors contributing to the suppressiveness of the soil in three treated Mutsumi soils (chloroform fumigated soil; autoclaved soil mixed with intact Mutsumi soil; and autoclaved soil mixed with intact, wilt-conducive Yamadai soil) infested with R. solanacearum, we bioassayed soil samples for tomato bacterial wilt. Chloroform fumigation increased the extent of wilt disease. More of the tomato plant samples wilted when mixed with Yamadai soil than when mixed with Mutsumi soil. Consequently, the results indicate that the naturally existing population of microorganisms in Mutsumi soil was significantly able to reduce the severity of bacterial wilt of tomato plants. To characterize the types of bacteria present at the rhizoplane, we isolated rhizoplane bacteria and classified them into 22 groups by comparing their 16S restriction fragment length polymorphism patterns. In Yamadai soil a single group of bacteria was extremely predominant (73.1%), whereas in Mutsumi soil the distribution of the bacterial groups was much more even. The 16S rDNA sequence analysis of strains of dominant groups suggested that gram-negative bacteria close to the beta-proteobacteria were most common at the rhizoplane of the tomato plants. During in vitro assays, rhizoplane bacteria in Mutsumi soil grew more vigorously on pectin, one of the main root exudates of tomato, compared with those in Yamadai soil. Our results imply that it is difficult for the pathogen to dominate in a diversified rhizobacterial community that thrives on pectin.     

Distinctive Bacterial Communities in the Rhizoplane of Four Tropical Tree Species

It is known that the microbial community of the rhizosphere is not only influenced by factors such as root exudates, phenology, and nutrient uptake but also by the plant species. However, studies of bacterial communities associated with tropical rainforest tree root surfaces, or rhizoplane, are lacking. Here, we analyzed the bacterial community of root surfaces of four species of native trees, Agathis borneensis, Dipterocarpus kerrii, Dyera costulata, and Gnetum gnemon, and nearby bulk soils, in a rainforest arboretum in Malaysia, using 454 pyrosequencing of the 16S rRNA gene. The rhizoplane bacterial communities for each of the four tree species sampled clustered separately from one another on an ordination, suggesting that these assemblages are linked to chemical and biological characteristics of the host or possibly to the mycorrhizal fungi present. Bacterial communities of the rhizoplane had various similarities to surrounding bulk soils. Acidobacteria, Alphaproteobacteria, and Betaproteobacteria were dominant in rhizoplane communities and in bulk soils from the same depth (0–10?cm). In contrast, the relative abundance of certain bacterial lineages on the rhizoplane was different from that in bulk soils: Bacteroidetes and Betaproteobacteria, which are known as copiotrophs, were much more abundant in the rhizoplane in comparison to bulk soil. At the genus level, Burkholderia, Acidobacterium, Dyella, and Edaphobacter were more abundant in the rhizoplane. Burkholderia, which are known as both pathogens and mutualists of plants, were especially abundant on the rhizoplane of all tree species sampled. The Burkholderia species present included known mutualists of tropical crops and also known N fixers. The host-specific character of tropical tree rhizoplane bacterial communities may have implications for understanding nutrient cycling, recruitment, and structuring of tree species diversity in tropical forests. Such understanding may prove to be useful in both tropical forestry and conservation.     

Response of fungal, bacterial and ureolytic communities to synthetic sheep urine deposition in a grassland soil

In grazed pastures, soil pH is raised in urine patches, causing dissolution of organic carbon and increased ammonium and nitrate concentrations, with potential effects on the structure and functioning of soil microbial communities. Here we examined the effects of synthetic sheep urine (SU) in a field study on dominant soil bacterial and fungal communities associated with bulk soil and plant roots (rhizoplane), using culture-independent methods and a new approach to investigate the ureolytic community. A differential response of bacteria and fungal communities to SU treatment was observed. The bacterial community showed a clear shift in composition after SU treatment, which was more pronounced in bulk soil than on the rhizoplane. The fungal community did not respond to SU treatment; instead, it was more affected by the time of sampling. Redundancy analysis of data indicated that the variation in the bacterial community was related to change in soil pH, while fungal community was more responsive to dissolution of organic carbon. Like the universal bacterial community, the ureolytic community was influenced by the SU treatment. However, different taxa within the ureolytic bacterial community responded differentially to the treatment. The ureolytic community comprised of members from a range of phylogenetically different taxa and could be used to measure the effect of environmental perturbations on the functional diversity of natural ecosystems.     

Effect of ferritin overexpression in tobacco on the structure of bacterial and pseudomonad communities associated with the roots

The genetic structures of total bacterial and pseudomonad communities were characterized in rhizosphere soil and rhizoplane+root tissues of tobacco wild type and a ferritin overexpressor transgenic line (P6) by a cultivation-independent method using directly extracted DNA at the end of three consecutive plant cultures. The structure of total bacterial communities was characterized by automated ribosomal intergenic spacer analysis (A-RISA), and that of pseudomonad communities was characterized by PCR-restriction fragment length polymorphism (PCR-RFLP) from DNA amplified with specific primers. The structure of total bacterial communities was significantly modified in the rhizosphere soil by the overaccumulation of iron in the tobacco transgenic P6 line at the first culture, to a lesser extent at the second culture, and not at all at the third culture. No significant difference was recorded between the total communities associated with the roots (rhizoplane+root tissues) of the two plant genotypes in any of the cultures. In contrast, the difference in pseudomonad structure between the two plant genotypes increased with successive culture at the root level, but was not detected at a significant level in the rhizosphere soil. The impact of iron overaccumulation by the tobacco transgenic P6 line on pseudomonads supports previous findings on the importance of iron competition among fluorescent pseudomonads.     

Investigations on rhizoplane Actinobacteria communities of papyrus (Cyperus papyrus) from an Egyptian wetland

Wetlands have important global ecological functions, which include carbon storage and water interception. Wetland contributes to the maintenance of regional and global biodiversity. Though many important wetland ecological functions are based on microbial metabolism, we have scanty knowledge on microbial diversity in wetlands. Plant rhizoplane habitats are considered to harbor highly diverse bacterial communities. Most of the floating mats on river Nile are dominated by papyrus (Cyperus papyrus). Papyrus root samples were collected from a floating mat at the "Gold Island" inside the Nile River at Cairo, Egypt in February 1996 and May 1997 in order to investigate the rhizoplane actinobacteria communities. The root-tip regions were cut off, repeatedly washed, macerated and plated. Using the plate-count technique with three actinobacteria media, an average of 2.1 x 10(4) CFUg-1 root actinobacteria were obtained. All actinobacteria colonies were isolated, purified and investigated by classical and molecular methods. In the papyrus rhizoplane Streptomyces anulatus, Micromonospora sp., Rhodococcus luteus, Verrucosispora gifhornensis and Aureobacterium liquefaciens dominated, moreover Actinoplanes utahensis, and Str. diastaticus were also present. The physiological traits of the members of dominant groups revealed that these bacteria might be active in the rhizoplane and can be present there is their vegetative forms.     

Root colonization of different plants by plant-growth-promoting Rhizobium leguminosarum bv. trifolii R39 studied with monospecific polyclonal antisera.

Monospecific polyclonal antisera raised against Rhizobium leguminosarum bv. trifolii R39, a bacterium which was isolated originally from red clover nodules, were used to study the colonization of roots of leguminous and nonleguminous plants (Pisum sativum, Lupinus albus, Triticúm aestivum, and Zea mays) after inoculation. Eight weeks after inoculation of soil-grown plants, between 0.1 and 1% of the total bacterial population in the rhizospheres of all inoculated plants were identified as R. leguminosarum bv. trifolii R39. To characterize the associative colonization of the nonleguminous plants by R.leguminosarum bv. trifolii R39 in more detail, a time course study was performed with inoculated roots of Z. mays. R. leguminosarum bv. trifolii R39 was found almost exclusively in the rhizosphere soil and on the rhizoplane 4 weeks after inoculation. Colonization of inner root tissues was detected only occasionally at this time. During the process of attachment of R. leguminosarum bv. trifolii R39 to the rhizoplane, bacterial lipopolysaccharides were overexpressed, and this may be important for plant-microbe interaction. Fourteen weeks after inoculation, microcolonies of R. leguminosarum bv. trifolii R39 were detected in lysed cells of the root cortex as well as in intracellular space of central root cylinder cells. At the beginning of flowering (18 weeks after inoculation), the number of R. leguminosarum bv. trifolii R39 organisms decreased in the rhizosphere soil, rhizoplane, and inner root tissue.     

Transgenic tobacco revealing altered bacterial diversity in the rhizosphere during early plant development

The rhizosphere constitutes a complex niche that may be exploited by a wide variety of bacteria. Bacterium–plant interactions in this niche can be influenced by factors such as the expression of heterologous genes in the plant. The objective of this work was to describe the bacterial communities associated with the rhizosphere and rhizoplane regions of tobacco plants, and to compare communities from transgenic tobacco lines (CAB1, CAB2 and TRP) with those found in wild-type (WT) plants. Samples were collected at two stages of plant development, the vegetative and flowering stages (1 and 3 months after germination). The diversity of the culturable microbial community was assessed by isolation and further characterization of isolates by amplified ribosomal RNA gene restriction analysis (ARDRA) and 16S rRNA sequencing. These analyses revealed the presence of fairly common rhizosphere organisms with the main groups Alphaproteobacteria, Betaproteobacteria, Actinobacteria and Bacilli. Analysis of the total bacterial communities using PCR-DGGE (denaturing gradient gel electrophoresis) revealed that shifts in bacterial communities occurred during early plant development, but the reestablishment of original community structure was observed over time. The effects were smaller in rhizosphere than in rhizoplane samples, where selection of specific bacterial groups by the different plant lines was demonstrated. Clustering patterns and principal components analysis (PCA) were used to distinguish the plant lines according to the fingerprint of their associated bacterial communities. Bands differentially detected in plant lines were found to be affiliated with the genera Pantoea, Bacillus and Burkholderia in WT, CAB and TRP plants, respectively. The data revealed that, although rhizosphere/rhizoplane microbial communities can be affected by the cultivation of transgenic plants, soil resilience may be able to restore the original bacterial diversity after one cycle of plant cultivation.     

Microbial Complexes Occurring on the Apogeotropic Roots and in the Rhizosphere of Cycad Plants

The microbial complexes of soil, the rhizosphere, and the rhizoplane of the apogeotropic (coralloid) roots of cycad plants were comparatively studied. The aseptically prepared homogenates of the surface-sterilized coralloid roots did not contain bacterial microsymbiont, indicating that in the root tissues the symbiosis is a two-component one (plant–cyanobacteria). At the same time, associated bacteria belonging to different taxonomic groups were detected in increasing amounts in the cycad rhizoplane, rhizosphere, and the surrounding soil. The bacterial communities found in the cycad rhizoplane and the surrounding soil were dominated by bacteria from the genus Bacillus. The saprotrophic bacteria and fungi colonizing the cycad rhizosphere and rhizoplane were dominated by microorganisms capable of degrading the plant cell walls. The local degradation of the cell wall was actually observed on the micrographs of the thin sections of cycad roots in the form of channels through which symbiotic cyanobacterial filaments can penetrate into the cortical parenchyma.