Bacterial endophytes in cotton: location and interaction with other plant-associated bacteria

Quadt-Hallmann, A.; Hallmann, Johannes; Kloepper, Joseph W.

doi:10.1139/m97-035

Cited by 101 publications

(55 citation statements)

References 8 publications

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“…In general, endophytic bacteria colonize the intercellular spaces and vascular systems of host plants, with only a few reports of intracellular colonization (9). Since endophytic bacteria are considered to compete with each other and with other endophytic organisms (such as fungi) for the limited space within the host plant (5,33), the endophytic bacteria that reside in seeds may have the advantage of being able to infect rapidly the next generation of plants.…”

Section: Resultsmentioning

confidence: 99%

Rice Seeds as Sources of Endophytic Bacteria

Mano²,

et al. 2009

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Endophytic bacteria are considered to originate from the external environment. To examine the hypothesis that rice (Oryza sativa, cultivar Kinuhikari) seeds are a source of endophytic bacteria, we isolated endophytic bacteria from the shoots, remains of the seeds, and roots of rice seedlings that were aseptically cultivated in vitro from surfacedisinfected seeds. Of the various bacterial strains isolated, the closest relatives, identified by 16S rRNA gene sequencing, were: Bacillus firmus, B. fusiformis, B. pumilus, Caulobacter crescentus, Kocuria palustris, Micrococcus luteus, Methylobacterium fujisawaense, Me. radiotolerans, and Pantoea ananatis. The latter three species have been detected frequently inside both rice seedlings and mature rice plants. These results indicate that rice seeds are an important source of endophytic bacteria. The bacteria that colonize the seed interior appear to infect the subsequent generation via rice seeds and become the dominant endophytic species in the mature plant.Key words: culturable endophytic bacteria, rice seed, infection from seed to shoot, 16S rRNA gene sequence Various types of microorganisms, including fungi, actinomycetes, and other bacteria, are found inside plants and designated endophytes. In general, microorganisms having visibly harmful effects on plants are not considered endophytes. Some endophytic bacteria have beneficial effects on the host, e.g., promoting plant growth, strengthening resistance to pathogens, and increasing the supply of fixed nitrogen to the plant (9). Studies are underway to exploit these beneficial features for agriculture. However, our knowledge of endophytic bacterial ecology, including the origins of these bacteria, remains incomplete.Endophytic bacteria are considered to originate from the external environment and to enter the plant through the stomata, lenticles, wounds (including broken trichomes), areas of emergence of lateral roots, and germinating radicles (12). The notion of seeds as a source of endophytic bacteria remains controversial (9). Sato (39) did not detect endophytic bacteria in rice seeds. Mundt and Hinkle (27) obtained endophytes only from the damaged seeds of 28 plant types other than rice. Endophytic bacteria were detected in cotton seeds at viable population densities that ranged from 1×10 3 to 1×105 CFU g −1 fresh weight, as well as in the seeds of sweet corn at viable population densities of <1×10 CFU g −1 fresh weight (26). Endophytic bacterial populations increased from nondetectable levels in cotton seeds to detectable levels in radicles 4 days after placing surface-disinfected cotton seeds on water agar (1).Rice (Oryza sativa) is the most important cereal crop in the world, feeding more than 50% of the global population (8). In our search for endophytic bacteria in rice plants, we detected culturable endophytic bacteria in rice seeds at viable population densities that ranged from 10 2 to 10 6 CFU g −1 fresh weight (22,31). Endophytes in seeds may be carried over to the subsequent generation. Thus, in the p...

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Section: Resultsmentioning

confidence: 99%

Rice Seeds as Sources of Endophytic Bacteria

Mano²,

et al. 2009

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“…It has previously been shown that endophytic communities vary spatially in the plant (9) or may be dependent on the interaction with other endophytic or pathogenic bacteria (29).…”

Section: Discussionmentioning

confidence: 99%

Diversity of Endophytic Bacterial Populations and Their Interaction withXylella fastidiosain Citrus Plants

Araújo

Marcon

Maccheroni

et al. 2002

Appl Environ Microbiol

512

354

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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.

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“…In addition, at a tissue level, the role of the cortex in root exudation versus that of the epidermis remains unknown. Although apoplastic loss may represent a slow diffusion pathway in comparison to direct loss from the epidermis (Canny 1995;Fleischer and Ehwald 1995), evidence suggests that gaps between epidermal cells (where apoplastic loss ultimately manifests itself) are strong regions of microbial colonization and therefore C availability (Quadt-Hallmann et al 1997;Watt et al 2006). Therefore more work is required to characterise apoplastic loss pathways from the root cortex and its contribution to maintaining the endo-and ectorhizosphere microbial community.…”

Section: Exudatesmentioning

confidence: 99%

Carbon flow in the rhizosphere: carbon trading at the soil–root interface

Jones

Nguyen²,

Finlay³

2009

Plant Soil

1,352

769

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The loss of organic and inorganic carbon from roots into soil underpins nearly all the major changes that occur in the rhizosphere. In this review we explore the mechanistic basis of organic carbon and nitrogen flow in the rhizosphere. It is clear that C and N flow in the rhizosphere is extremely complex, being highly plant and environment dependent and varying both spatially and temporally along the root. Consequently, the amount and type of rhizodeposits (e.g. exudates, border cells, mucilage) remains highly context specific. This has severely limited our capacity to quantify and model the amount of rhizodeposition in ecosystem processes such as C sequestration and nutrient acquisition. It is now evident that C and N flow at the soil-root interface is bidirectional with C and N being lost from roots and taken up from the soil simultaneously. Here we present four alternative hypotheses to explain why high and low molecular weight organic compounds are actively cycled in the rhizosphere. These include:(1) indirect, fortuitous root exudate recapture as part of the root's C and N distribution network, (2) direct re-uptake to enhance the plant's C efficiency and to reduce rhizosphere microbial growth and pathogen attack, (3) direct uptake to recapture organic nutrients released from soil organic matter, and (4) for interroot and root-microbial signal exchange. Due to severe flaws in the interpretation of commonly used isotopic labelling techniques, there is still great uncertainty surrounding the importance of these individual fluxes in the rhizosphere. Due to the importance of rhizodeposition in regulating ecosystem functioning, it is critical that future research focuses on resolving the quantitative importance of the different C and N fluxes operating in the rhizosphere and the ways in which these vary spatially and temporally.

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Bacterial endophytes in cotton: location and interaction with other plant-associated bacteria

Cited by 101 publications

References 8 publications

Rice Seeds as Sources of Endophytic Bacteria

Rice Seeds as Sources of Endophytic Bacteria

Diversity of Endophytic Bacterial Populations and Their Interaction withXylella fastidiosain Citrus Plants

Carbon flow in the rhizosphere: carbon trading at the soil–root interface

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