Diversity of Endophytic Bacterial Populations and Their Interaction with Xylella fastidiosa in Citrus Plants

Citrus variegated chlorosis (CVC) is caused by Xylella fastidiosa, a phytopathogenic bacterium that can infect all Citrus sinensis cultivars. The endophytic bacterial communities of healthy, resistant, and CVC-affected citrus plants were studied by using cultivation as well as cultivation-independent techniques. The endophytic communities were assessed in surface-disinfected citrus branches by plating and denaturing gradient gel electrophoresis (DGGE). Dominant isolates were characterized by fatty-acid methyl ester analysis as Bacillus pumilus, Curtobacterium flaccumfaciens, Enterobacter cloacae, Methylobacterium spp. (including Methylobacterium extorquens, M. fujisawaense, M. mesophilicum, M. radiotolerans, and M. zatmanii), Nocardia sp., Pantoea agglomerans, and Xanthomonas campestris. We observed a relationship between CVC symptoms and the frequency of isolation of species of Methylobacterium, the genus that we most frequently isolated from symptomatic plants. In contrast, we isolated C. flaccumfaciens significantly more frequently from asymptomatic plants than from those with symptoms of CVC while P. agglomerans was frequently isolated from tangerine (Citrus reticulata) and sweet-orange (C. sinensis) plants, irrespective of whether the plants were symptomatic or asymptomatic or showed symptoms of CVC. DGGE analysis of 16S rRNA gene fragments amplified from total plant DNA resulted in several bands that matched those from the bacterial isolates, indicating that DGGE profiles can be used to detect some endophytic bacteria of citrus plants. However, some bands had no match with any isolate, suggesting the occurrence of other, nonculturable or as yet uncultured, endophytic bacteria. A specific band with a high G+C ratio was observed only in asymptomatic plants. The higher frequency of C. flaccumfaciens in asymptomatic plants suggests a role for this organism in the resistance of plants to CVC.     

柑橘黄龙病寄主长春花内生细菌的分离及功能鉴定

【目的】感柑橘黄龙病长春花植株与健康长春花植株不同部位内生细菌菌群结构及功能对柑橘黄龙病菌与长春花内生细菌的相关性研究提供理论基础。【方法】利用兼性厌氧可培养技术以及植物内生菌功能特性分析相结合的方法。【结果】分别从感病和健康长春花叶、茎、根的组织中分离获得67株内生细菌,与GenBank中29种细菌的相似性达到97%-100%。其中短小杆菌属(Curtobacterium sp.)、欧文氏菌属(Erwinia sp.)、蜡样芽胞杆菌(Bacillus cereus)为感病长春花内生细菌的优势菌群,鞘胺醇单胞菌属(Brevundimonas sp.)、芽胞杆菌属(Bacillus sp.)为健康长春花内生细菌的优势菌群;马胃葡萄球菌(Staphylococcus equorum)为两者的共同优势菌群。29种内生细菌进行功能分析,其中6株内生细菌至少具有4种功能特性,分属于马胃葡萄球菌、苏云金芽孢杆菌、巨大芽孢杆菌、短小杆菌属、摩氏摩根菌(Morganella morganii)及溶杆菌属(Lysobacter sp.)5个属。【结论】感病与健康长春花植株中均含有丰富的内生细菌且差异较大,黄龙病菌的存在改变了长春花原有内生细菌的菌群结构。通过分析菌群的差异,有望找到与柑橘黄龙病菌生长相关的菌种。     

Isolation,partial characterization,and the effect of plant growth-promoting bacteria (PGPB) on micro-propagated sugarcane in vitro

We report the isolation of nitrogen fixing, phytohormone producing bacteria from sugarcane and their beneficial effects on the growth of micropropagated sugarcane plantlets. Detection of the nitrogen fixing bacteria by ARA-based MPN (acetylene reduction assay-based most probable number) method indicated the presence of up to 10⁶ bacteria per gram dry weight of stem and 10⁷ bacteria per gram dry weight of root of field-grown sugarcane. Two nitrogen fixing bacterial isolates were obtained from stem (SC11, SC20) and two from the roots (SR12, SR13) of field-grown plants. These isolates were identified as Enterobacter sp. strains on the basis of their morphological characteristics and biochemical tests. The isolate SC20 was further characterized by 16S rRNA sequence analysis, which showed high sequence similarity to the sequence of Enterobacter cloacae and Klebsiella oxytoca. All the isolates produced the phytohormone indoleacetic acid (IAA) in pure culture and this IAA production was enhanced in growth medium containing tryptophan. The bacterial isolates were used to inoculate micro-propagated sugarcane in vitro where maximum increase in the root and shoot weight over control was observed in the plantlets inoculated with strain SC20. By using the¹⁵N isotope dilution technique, maximum nitrogen fixation contribution (28% of total plant nitrogen) was detected in plantlets inoculated with isolate SC20.     

Botanicals,selective insecticides,and predators to control Diaphorina citri （Hemiptera： Liviidae） in citrus orchards

The Asian citrus psyllid （ACP） Diaphorina citri Kuwayama vectors pathogens that cause huanglongbing （HLB） or citrus greening devastating and economically im- portant disease present in most citrus growing regions. Young citrus shoots are required for psyllid reproduction and development. During winter citrus trees produce little or no new growth. Overwintering adults reproduce in spring on newly emerging shoots also attractive to other pests and beneficial insects. Botanicals and relatively selective insecti- cides could help to conserve beneficial insects and reduce pest resistance to insecticides. Sprays of Azadirachtin （Neem）, Tropane （Datura）, Spirotetramat, Spinetoram, and broad- spectrum Imidacloprid were evaluated to control ACP in spring and summer on 10-year-old ＂Kinow＂ Citrus reticulata Blanco trees producing new growth. Psyllid populations were high averaging 5-9 nymphs or adults per sample before treatment application. Nymphs or adults were significantly reduced to 0.5-1.5 per sample in all treatments for 3 weeks, aver- age 61%-83% reduction. No significant reduction in ladybeetles Adalia bipunctata, Ane- glei scardoni, Cheilomenes sexmaculata, and Coccinella septempunctata was observed. Syrphids, spiders and green lacewings were reduced in treated trees except with Tropane. Studies are warranted to assess impact of these predators on ACP and interaction with insecticides. Observed reduction in ACP populations may not be enough considering its reproductive potential and role in the spread of HLB. Follow-up sprays may be required to achieve additional suppression using rotations of different insecticides.     

Asian citrus psyllid,Diaphorina citri,vector of citrus huanglongbing disease

The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Psyllidae), is an important pest of citrus because it transmits phloem‐limited bacteria [Candidatus Liberibacter spp., notably Ca. L. asiaticus (LAS)] associated with huanglongbing (HLB; citrus greening disease), currently considered the world's most serious disease of citrus. Asian citrus psyllid transmits LAS in a persistent manner and, although the rate of LAS transmission by ACP individuals usually is low, HLB can spread rapidly in a citrus grove and the geographic range of the disease is expanding, threatening citrus industries in new areas. Intensive chemical control of ACP is the primary management strategy currently advocated for HLB, but this strategy is costly, unsustainable, and generally ineffective. The scientific community is searching aggressively for solutions to HLB on many fronts, but it could still be years before solutions are found and implemented. Plant resistance to LAS is one area of research being pursued, whereby traits that confer resistance are identified and incorporated into citrus germplasm through conventional or transgenic methods. It remains to be seen if a solution to HLB can be found that specifically targets ACP, but research on ACP has been stepped up in a number of areas, notably on ACP–LAS–plant interactions, on host plant resistance to ACP, and on molecular methods of silencing ACP genes to induce mortality or to block its ability to transmit HLB‐causing bacteria. Advancements in these and other research areas may depend greatly on a better understanding of basic ACP biology and vector–pathogen–host plant interactions at the molecular, cellular, and community levels. Here, we present an updated review of ACP and HLB with an emphasis on the problem in Florida.     

Isolation and characterization of root-associated bacteria from agricultural crops in the Kavango region of Namibia

Root-associated bacteria can have beneficial effects on their host plants. Microbial products can promote and stimulate plant growth or lead to bioprotection against pathogens. This study aimed to isolate putatively beneficial bacteria from traditional cereals grown by subsistence farmers in the Kavango of Namibia. Bacteria were isolated from surface-sterilized roots of Pennisetum glaucum, Sorghum bicolor, and Zea mays, and subjected to phenotypic and phylogenetic analyses. A total of 44 root-associated bacterial strains were isolated. From 33 distinct isolates, 22 belonged to Firmicutes and Actinobacteria, while 11 were Proteobacteria. Eleven novel phylotypes were among the isolates. Features known to contribute to plant growth-promotion and biocontrol were tested in vitro and revealed promising candidates with multiple beneficial characteristics. This is the first report on the characterization of native isolates associated with important agriculture crops in the Kavango region of Namibia. Such isolates have the potential for application as inoculants adapted to poor soils and local crops. Desiccation-tolerant or sporulating Gram-positive bacteria are of particular interest for this region, which is characterized by a long dry season.     

Diversity of endophytic bacterial populations and their interaction with Xylella fastidiosa in citrus plants

Citrus variegated chlorosis (CVC) is caused by Xylella fastidiosa, a phytopathogenic bacterium that can infect all Citrus sinensis cultivars. The endophytic bacterial communities of healthy, resistant, and CVC-affected citrus plants were studied by using cultivation as well as cultivation-independent techniques. The endophytic communities were assessed in surface-disinfected citrus branches by plating and denaturing gradient gel electrophoresis (DGGE). Dominant isolates were characterized by fatty-acid methyl ester analysis as Bacillus pumilus, Curtobacterium flaccumfaciens, Enterobacter cloacae, Methylobacterium spp. (including Methylobacterium extorquens, M. fujisawaense, M. mesophilicum, M. radiotolerans, and M. zatmanii), Nocardia sp., Pantoea agglomerans, and Xanthomonas campestris. We observed a relationship between CVC symptoms and the frequency of isolation of species of Methylobacterium, the genus that we most frequently isolated from symptomatic plants. In contrast, we isolated C. flaccumfaciens significantly more frequently from asymptomatic plants than from those with symptoms of CVC while P. agglomerans was frequently isolated from tangerine (Citrus reticulata) and sweet-orange (C. sinensis) plants, irrespective of whether the plants were symptomatic or asymptomatic or showed symptoms of CVC. DGGE analysis of 16S rRNA gene fragments amplified from total plant DNA resulted in several bands that matched those from the bacterial isolates, indicating that DGGE profiles can be used to detect some endophytic bacteria of citrus plants. However, some bands had no match with any isolate, suggesting the occurrence of other, nonculturable or as yet uncultured, endophytic bacteria. A specific band with a high G+C ratio was observed only in asymptomatic plants. The higher frequency of C. flaccumfaciens in asymptomatic plants suggests a role for this organism in the resistance of plants to CVC.     

Root bacteria from nematicidal plants and their biocontrol potential against trichodorid nematodes in potato

Trichodorid nematodes (Nematoda: Trichodoridae) are vectors of tobacco rattle virus (TRV), one of the causal agents of spraing disease in potato. Root bacteria from nematicidal plants and their control potential against Trichodoridae were the focus of this study. Bacteria isolated from the roots of 12 nematicidal plants and potato were characterized for their production of hydrolytic enzymes, hydrogen cyanide, phenol oxidation ability and antifungal activity towards the potato pathogen Rhizoctonia solani. Based on these functional traits, bacteria isolates were selected and tested in greenhouse conditions on potato (cv. Saturna) for their effect on plant growth, and screened for nematicidal activity against Paratrichodorus pachydermus and Trichodorus primitivus in naturally infested soil. Sixteen bacteria isolates out of 44 reduced nematode densities by 50–100%. Nine selected isolated were further tested by bacterizing potato tubers (cv. King Edward) which were planted in a trichodorid and TRV-infested soil. Four bacterial isolates consistently reduced nematode densities (by 56.7–74.4%) with no visual negative effect on plant growth. These isolates were tentatively identified, partly by fatty acid methyl ester (FAME) analysis as: Stenotrophomonas maltophilia, Bacillus mycoides, Pseudomonas sp., and one unidentified bacterium. The isolates originated from potato, Plantago major, Thymus vulgaris and Asparagus officinalis, respectively. Two Pseudomonas isolates obtained from Zinnia elegans and selected for their strong nematicidal activity in soil screening tests, did not reduce the nematode population when tested on potato. It is concluded that plants releasing nematicidal compounds may harbour nematode-antagonistic bacteria as well.     

The Genetic Diversity of Culturable Nitrogen-Fixing Bacteria in the Rhizosphere of Wheat

A total of 17 culturable nitrogen-fixing bacterial strains associated with the roots of wheat growing in different regions of Greece were isolated and characterized for plant-growth-promoting traits such as auxin production and phosphate solubilization. The phylogenetic position of the isolates was first assessed by the analysis of the PCR-amplified 16S rRNA gene. The comparative sequence analysis and phylogenetic analysis based on 16S rRNA gene sequences show that the isolates recovered in this study are grouped with Azospirillum brasilense, Azospirillum zeae, and Pseudomonas stutzeri. The diazotrophic nature of all isolates was confirmed by amplification of partial nifH gene sequences. The phylogenetic tree based on nifH gene sequences is consistent with 16S rRNA gene phylogeny. The isolates belonging to Azospirillum species were further characterized by examining the partial dnaK gene phylogenetic tree. Furthermore, it was demonstrated that the ipdC gene was present in all Azospirillum isolates, suggesting that auxin is mainly synthesized via the indole-3-pyruvate pathway. Although members of P. stutzeri and A. zeae are known diazotrophic bacteria, to the best of our knowledge, this is the first report of isolation and characterization of strains belonging to these bacterial genera associated with wheat.     

Free-living culturable bacteria and protozoa from the rhizoplanes of three floating aquatic plant species

Terrestrial plant roots exude compounds that promote the proliferation of microorganisms, a phenomenon called the rhizosphere effect. However, little is known about the influence of roots of aquatic plants on microbial populations. We compared cultivable bacteria and protozoa from the rhizoplanes of Azolla filiculoides Lam., Lemna gibba L., and Ricciocarpus natans L., collected at the Tecocomulco Lagoon (Hidalgo, Mexico). The functional bacterial groups isolated from A. filiculoides, L. gibba and R. natans, were macro- and microscopically characterized, and phylogenetically identified using the 16S rDNA gen. About 96% of isolates corresponded to Gram-negative bacteria, and potential N-fixing free-living bacteria (diazotrophic bacteria) were the most abundant. Molecular analysis detected 15 bacterial genera in the rhizoplane of R. natans, whereas A. filiculoides and L. gibba only yielded five genera, among which Aeromonas was predominant. Twenty-five genera of flagellated and 20 genera of ciliated protozoa were identified. Bodo was the more abundant flagellated, whereas Halteria was the most frequent ciliate. All three aquatic plants showed the rhizospheric effects. The most abundant and diverse community of protozoa was found in A. filiculoides, which also had the most abundant bacterial community, but the highest bacterial diversity was found in R. natans.     

Isolation and characterization of halophilic bacteria from Urmia Lake in Iran

Urmia Lake is one of the most permanent hypersaline lakes in the world which is threatened by hypersalinity and serious dryness. In spite of its importance no paper has been published regarding bacterial community of this lake. Accordingly, the present study aimed to investigate the halophilic bacteria in the aforementioned lake. In so doing, thirty seven strains were isolated on six different culture media. The isolated strains were characterized using phenotypic and genotypic methods. Growth of the strains occurred at 25–35°C, pH 6–9 and 7 to 20% (w/v) NaCl indicating that most of the isolates were moderately halophiles. Catalase, oxidase and urease activities were found to be positive for the majority of the isolates. Phylogenetic analysis based on 16S rRNA gene sequences indicated that the isolated bacteria belonged to two major taxa: Gammaproteobacteria (92%, including Salicola [46%], Pseudomonas [13.5%], Marinobacter [11%], Idiomarina [11%], and Halomonas [8%]) and Firmicutes (8%, including Bacillus [5%] and Halobacillus [3%]). In addition, a novel bacterium whose 16S rRNA gene sequence showed almost 98% sequence identity with the taxonomically troubled DSM 3050^T, Halovibrio denitrificans HGD 3^T and Halospina denitriflcans HGD 1–3, each, was isolated. 16S rRNA gene similarity levels along with phenotypic characteristics suggest that some of the isolated strains could be regarded as potential type strain for novel species, on which further studies are recommended.     

Isolation of Bacterial Antagonists of Aspergillus flavus from Almonds

Bacteria were isolated from California almond orchard samples to evaluate their potential antifungal activity against aflatoxin-producing Aspergillus flavus. Fungal populations from the same samples were examined to determine the incidence of aflatoxigenic Aspergillus species. Antagonistic activities of the isolated bacterial strains were screened against a nonaflatoxigenic nor mutant of A. flavus, which accumulates the pigmented aflatoxin precursor norsolorinic acid (NOR) under conditions conducive to aflatoxin production. Using solid and liquid media in coculture assays, 171 bacteria isolated from almond flowers, immature nut fruits, and mature nut fruits showed inhibition of A. flavus growth and/or inhibition of NOR accumulation. Bacterial isolates were further characterized for production of extracellular enzymes capable of hydrolyzing chitin or yeast cell walls. Molecular and physiological identification of the bacterial strains indicated that the predominant genera isolated were Bacillus, Pseudomonas, Ralstonia, and Burkholderia, as well as several plant-associated enteric and nonenteric bacteria. A set of 20 isolates was selected for further study based on their species identification, antifungal phenotypes, and extracellular enzyme production. Quantitative assays using these isolates in liquid coculture with a wild-type, aflatoxin-producing A. flavus strain showed that a number of strains completely inhibited fungal growth in three different media. These results indicate the potential for development of bacterial antagonists as biological control agents against aflatoxigenic aspergilli on almonds.     

In vitro egg hatching of Diaphorina citri,the vector of Huanglongbing

Citrus greening (Huanglongbing, HLB) is a destructive disease associated with the uncultivable, phloem-limited, gram-negative bacteria Candidatus Liberibacter spp., which affects citrus crops and other Rutaceae species. HLB is rapidly transmitted by the Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae). We developed an artificial medium on which D. citri eggs can hatch and first-instar nymphs can feed. The medium could be used to study insect physiology and screen molecules that may interfere with egg hatching and nymph development.     

Infection and distribution of Candidatus Liberibacter asiaticus in citrus plants and psyllid vectors at the cellular level

Huanglongbing (HLB) is currently considered the most destructive disease of citrus worldwide. In the major citrus-growing areas in Asia and the US, the major causal agent of HLB is the bacterial pathogen Candidatus Liberibacter asiaticus (CLas). CLas is vectored by the Asian citrus psyllid, Diaphorina citri, in a persistent propagative manner. CLas cannot be cultured in vitro because of its unclear growth factors, leading to uncertainty in the infection mechanism of CLas at the cellular level in citrus and in D. citri. To characterize the detailed infection of CLas in the host and vector, the incidence of HLB was first investigated in citrus-growing fields in Fujian Province, China. It was found that the positive association of the level of CLas infection in the leaves correlated with the symptoms. Then antibodies against peptides of the outer membrane protein (OMP) of CLas were prepared and tested. The antibodies OMP-225, OMP-333 and OMP724 showed specificity to citrus plants in western blot analyses, whereas the antibodies OMP-47 and OMP-225 displayed specificity to the D. citri vector. The application of OMP-225 in the immunofluorescence assay indicated that CLas was located in and distributed throughout the phloem sieve cells of the leaf midribs and axile placenta of the fruit. CLas also infected the epithelial cells and visceral muscles of the alimentary canal of D. citri. The application of OMP-333 in immunoelectron microscopy indicated the round or oval CLas in the sieve cells of leaf midribs and axile placenta of fruit as well as in the epithelial cells and reticular tissue of D. citri alimentary canal. These results provide a reliable means for HLB detection, and enlighten a strategy via neutralizing OMP to control HLB. These findings also provide insight for the further investigation on CLas infection and pathogenesis, as well as CLas–vector interaction.     

Actinomycetales bacteria from a spruce stand: Characterization and effects on growth of root symbiotic and plant parasitic soil fungi in dual culture

The rhizosphere, the narrow zone of soil around living roots, is characterized by root exudates which attract soil microorganisms. Most importantly, certain soil fungi establish symbiotic interactions with fine roots which enhance nutrient availability for the plant partner (mycorrhiza). The establishment of such a symbiosis can be affected by soil bacteria. In this study we isolated Gram-positive soil bacteria from the rhizosphere of a spruce stand rich with fly agaric (Amanita muscaria) fruiting bodies. Using a coculture technique in Petri dishes, bacterial isolates were characterized by their effect on the growth of fungal hyphae. A group of bacterial strains were identified which significantly promoted growth of fly agaric hyphae. One of these strains was shown to additionally inhibit growth of pathogenic fungi such as Armillaria obscura (wide host range) and Heterobasidion annosum (causes wood decay in conifers). Taxonomic characterization of the effective bacterial isolates by their morphological appearance, by the analysis of diaminopimelic acid, cell wall sugars, and DNA sequencing (16S rDNA) identified them as actinomycetes, some of which are not yet contained in data banks.     

Characterization of Plant Growth–Promoting Traits of Bacteria Isolated from Larval Guts of Diamondback Moth <Emphasis Type="Italic">Plutella xylostella</Emphasis> (Lepidoptera: Plutellidae)

Eight bacterial isolates from the larval guts of Diamondback moths (Plutella xylostella) were tested for their plant growth–promoting (PGP) traits and effects on early plant growth. All of the strains tested positive for nitrogen fixation and indole 3-acetic acid (IAA) and salicylic acid production but negative for hydrogen cyanide and pectinase production. In addition, five of the isolates exhibited significant levels of tricalcium phosphate and zinc oxide solubilization; six isolates were able to oxidize sulfur in growth media; and four isolates tested positive for chitinase and β-1,3-glucanase activities. Based on their IAA production, six strains including four that were 1-aminocyclopropane-1-carboxylate (ACC) deaminase positive and two that were ACC deaminase negative were tested for PGP activity on the early growth of canola and tomato seeds under gnotobiotic conditions. Acinetobacter sp. PSGB04 significantly increased root length (41%), seedling vigor, and dry biomass (30%) of the canola test plants, whereas Pseudomonas sp. PRGB06 inhibited the mycelial growth of Botrytis cinerea, Colletotrichum coccodes, C. gleospoiroides, Rhizoctonia solani, and Sclerotia sclerotiorum under in vitro conditions. A significant increase, greater than that of the control, was also noted for growth parameters of the tomato test plants when the seeds were treated with PRGB06. Therefore, the results of the present study suggest that bacteria associated with insect larval guts possess PGP traits and positively influence plant growth. Therefore, insect gut bacteria as effective PGP agents represent an unexplored niche and may broaden the spectrum of beneficial bacteria available for crop production.     

Presence and abundance of Diaphorina citri in Murraya paniculata in urban areas free of huanglongbing in Brazil

Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Liviidae), is the vector of the bacterium Candidatus Liberibacter sp., a quarantine pathogen in citrus production areas such as Australia, Europe, and northeast Brazil, associated with huanglongbing (HLB). The psyllids’ preferred host is Murraya paniculata (L.) Jacq. (Rutaceae), an ornamental plant native to Asia and Oceania, and commonly found in urban areas next to citrus groves around the world. As there are insecticide application restrictions for urban areas, monitoring and use of biological control to suppress ACP are essential for an area-wide HLB management strategy, especially for production areas predominantly composed of small citrus farms. For this, it is necessary to understand the occurrence cycles of ACP and vegetative flush of the ornamental host. This study characterized the occurrence cycles of M. paniculata flush shoot and accumulated rainfall, and the association with ACP presence (proportion of monitored trees) and abundance (per tree) in a Brazilian urban area free of HLB. A 3-year time series was constructed using spectral and co-spectral analysis. Spectral analysis showed the occurrence of at least seven flush shoot cycles of M. paniculata, nearly 10 ACP presence and abundance cycles, and monthly cycles of accumulated rainfall. Cycles of ACP presence were associated with ACP abundance, with ACP presence cycles occurring around 7 days before ACP abundance cycles and the correlation and co-spectral analyses indicated an almost simultaneous occurrence of the main cycles of M. paniculata flush shoots and ACP occurrence. These findings will facilitate the development of an ACP biological control program based on parasitoid releases in urban areas in HLB-free citrus groves.     

喀斯特石漠化治理区钙果种植年限对根内细菌群落的影响

存在于健康植物根中的内生细菌不但能够与宿主植物建立共生关系,而且还具有促进植物生长、提升植物对营养元素摄取能力等功能,从而对维持陆地生态平衡、提升喀斯特石漠化综合治理成效具有重要的意义。【目的】探究宿主植物根中的内生细菌群落结构,为深入认识宿主植物-内生细菌的互作机制提供理论依据。【方法】以被引种到喀斯特断陷盆地石漠化综合治理区不同种植年限钙果根中的内生细菌和根际土为研究对象,分析根内生细菌群落特征和根际土理化性质。【结果】钙果种植年限对研究区土壤质量整体有着直接、显著的影响,并间接影响根内生细菌群落。根内生细菌群落以共生互作为主,通过共网络结构识别出种植第一年和第三年的前三位优势属为链霉菌属(Streptomyces)、卡氏伯克霍尔德菌属(Burkholderia-Caballeronia- Paraburkholderia)和噬几丁质菌属(Chitinophaga),种植第五年的前三位优势属为Streptomyces、Chitinophaga和海无柄孢囊黏细菌属(Haliangium)。根内生细菌群落的形成主要由随机性过程中的生态漂变所主导。【结论】不同生长阶段钙果根内生细菌群落结构的差异是由于随机性过程赋予了微生物物种多样化。内生细菌群落的共生互作关系以及优势菌具有生防功能,可增强钙果定殖能力和生长,进而提升钙果在喀斯特断陷盆地石漠化综合治理区的生态效益和经济效益。     

Molecular characterization of early colonizer bacteria from wastes in a steel plant

Aims: Forty‐nine bacteria isolated from four newly‐produced waste samples of a steel industry, which had a high content of CaO, MgO, Cr and P₂O₅, were characterized molecularly and phenotypically by susceptibility testing against heavy metals. Methods and Results: Phylogenetic analysis using 16S rRNA gene sequences revealed that the isolates belonged to nine genera, Pseudomonas, Micrococcus, Acinetobacter, Bacillus, Dietzia, Kocuria, Diaphorobacter, Staphylococcus and Brevibacillus. Besides, some isolates could be affiliated to species: M. luteus, Ac. junii, Ac. schindleri, B. cereus, K. marina, D. nitroreducens and Staph. warneri. The bacteria that were characterized are taxonomically diverse, and Pseudomonas and Micrococcus predominated. Fingerprinting BOX‐PCR revealed high genomic heterogeneity among the isolates. Among the heavy metal compounds Zn, Ni, Pb and Cu were least toxic to the bacterial isolates, whereas Ag inhibited all isolates at 0·001 mmol l^?1. Conclusions: Heterotrophic bacteria, affiliated with several phylogentic groups, were able to colonize different wastes of a steel industry. Significance and Impact of the Study: This study extends our knowledge of the early colonizers bacteria populating siderurgic environments. Some of these bacteria could have potential for recycling siderurgic waste for steel production.