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Endophytic Actinobacteria and the Interaction of Micromonospora and Nitrogen Fixing Plants.

Trujillo ME, Riesco R, Benito P, Carro L - Front Microbiol (2015)

Bottom Line: For a long time, it was believed that a healthy plant did not harbor any microorganisms within its tissues, as these were often considered detrimental for the plant.Micromonospora is a Gram-positive bacterium with a wide geographical distribution; it can be found in the soil, mangrove sediments, and freshwater and marine ecosistems.Unexpectedly, a high number of plant-cell wall degrading enzymes were also detected, a trait usually found only in pathogenic bacteria.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Microbiología y Genética, Universidad de Salamanca Salamanca, Spain.

ABSTRACT
For a long time, it was believed that a healthy plant did not harbor any microorganisms within its tissues, as these were often considered detrimental for the plant. In the last three decades, the numbers of studies on plant microbe-interactions has led to a change in our view and we now know that many of these invisible partners are essential for the overall welfare of the plant. The application of Next Generation Sequencing techniques is a powerful tool that has permitted the detection and identification of microbial communities in healthy plants. Among the new plant microbe interactions recently reported several actinobacteria such as Micromonospora are included. Micromonospora is a Gram-positive bacterium with a wide geographical distribution; it can be found in the soil, mangrove sediments, and freshwater and marine ecosistems. In the last years our group has focused on the isolation of Micromonospora strains from nitrogen fixing nodules of both leguminous and actinorhizal plants and reported for the first time its wide distribution in nitrogen fixing nodules of both types of plants. These studies have shown how this microoganism had been largely overlooked in this niche due to its slow growth. Surprisingly, the genetic diversity of Micromonospora strains isolated from nodules is very high and several new species have been described. The current data indicate that Micromonospora saelicesensis is the most frequently isolated species from the nodular tissues of both leguminous and actinorhizal plants. Further studies have also been carried out to confirm the presence of Micromonospora inside the nodule tissues, mainly by specific in situ hybridization. The information derived from the genome of the model strain, Micromonospora lupini, Lupac 08, has provided useful information as to how this bacterium may relate with its host plant. Several strategies potentially necessary for Micromonospora to thrive in the soil, a highly competitive, and rough environment, and as an endophytic bacterium with the capacity to colonize the internal plant tissues which are protected from the invasion of other soil microbes were identified. The genome data also revealed the potential of M. lupini Lupac 08 as a plant growth promoting bacterium. Several loci involved in plant growth promotion features such as the production of siderophores, phytohormones, and the degradation of chitin (biocontrol) were also located on the genome and the functionality of these genes was confirmed in the laboratory. In addition, when several host plants species were inoculated with Micromonospora strains, the plant growth enhancing effect was evident under greenhouse conditions. Unexpectedly, a high number of plant-cell wall degrading enzymes were also detected, a trait usually found only in pathogenic bacteria. Thus, Micromonospora can be added to the list of new plant-microbe interactions. The current data indicate that this microorganism may have an important application in agriculture and other biotechnological processes. The available information is promising but limited, much research is still needed to determine which is the ecological function of Micromonospora in interaction with nitrogen fixing plants.

No MeSH data available.


Related in: MedlinePlus

Maximum-likelihood phylogenetic tree based on 16S rRNA gene sequences of Micromonospora species isolated from plant material and rhizospheric soil. There were 1408 nucleotides in the final dataset. Analyses were carried in MEGA 6 software. Bar indicates 0.005 substitutions per nucleotide position (Based on references provided in Table 2).
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Figure 2: Maximum-likelihood phylogenetic tree based on 16S rRNA gene sequences of Micromonospora species isolated from plant material and rhizospheric soil. There were 1408 nucleotides in the final dataset. Analyses were carried in MEGA 6 software. Bar indicates 0.005 substitutions per nucleotide position (Based on references provided in Table 2).

Mentions: The degree of genetic variation of Micromonospora strains recovered from the nitrogen-fixing nodules of various plants was analyzed using several molecular typing techniques (e.g., BOX–PCR, ARDRA, RFLP, RAPDS) (Cerda, 2008; Carro, 2009; Alonso de la Vega, 2010; Trujillo et al., 2010; Carro et al., 2012a; Martínez-Hidalgo et al., 2014). Highly diverse genetic fingerprint profiles were found among the isolates studied, indicating that they were not clones; the diversity found was unexpectedly high considering that in some cases, the strains analyzed were isolated from the same nodule (Alonso de la Vega, 2010). Subsequently, taxonomic studies carried for some of these isolates confirmed that many of these bacterial strains represented new species and include Micromonospora coriariae (Trujillo et al., 2006); Micromonospora lupini and Micromonospora saelicesensis (Trujillo et al., 2007); Micromonospora pisi (Garcia et al., 2010); Micromonospora cremea, Micromonospora zamorensis, and Micromonospora halotolerans (Figure 2). The latter three strains were isolated from the rhizospheric soil of the sampled plants (Carro et al., 2012b, 2013b).


Endophytic Actinobacteria and the Interaction of Micromonospora and Nitrogen Fixing Plants.

Trujillo ME, Riesco R, Benito P, Carro L - Front Microbiol (2015)

Maximum-likelihood phylogenetic tree based on 16S rRNA gene sequences of Micromonospora species isolated from plant material and rhizospheric soil. There were 1408 nucleotides in the final dataset. Analyses were carried in MEGA 6 software. Bar indicates 0.005 substitutions per nucleotide position (Based on references provided in Table 2).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4664631&req=5

Figure 2: Maximum-likelihood phylogenetic tree based on 16S rRNA gene sequences of Micromonospora species isolated from plant material and rhizospheric soil. There were 1408 nucleotides in the final dataset. Analyses were carried in MEGA 6 software. Bar indicates 0.005 substitutions per nucleotide position (Based on references provided in Table 2).
Mentions: The degree of genetic variation of Micromonospora strains recovered from the nitrogen-fixing nodules of various plants was analyzed using several molecular typing techniques (e.g., BOX–PCR, ARDRA, RFLP, RAPDS) (Cerda, 2008; Carro, 2009; Alonso de la Vega, 2010; Trujillo et al., 2010; Carro et al., 2012a; Martínez-Hidalgo et al., 2014). Highly diverse genetic fingerprint profiles were found among the isolates studied, indicating that they were not clones; the diversity found was unexpectedly high considering that in some cases, the strains analyzed were isolated from the same nodule (Alonso de la Vega, 2010). Subsequently, taxonomic studies carried for some of these isolates confirmed that many of these bacterial strains represented new species and include Micromonospora coriariae (Trujillo et al., 2006); Micromonospora lupini and Micromonospora saelicesensis (Trujillo et al., 2007); Micromonospora pisi (Garcia et al., 2010); Micromonospora cremea, Micromonospora zamorensis, and Micromonospora halotolerans (Figure 2). The latter three strains were isolated from the rhizospheric soil of the sampled plants (Carro et al., 2012b, 2013b).

Bottom Line: For a long time, it was believed that a healthy plant did not harbor any microorganisms within its tissues, as these were often considered detrimental for the plant.Micromonospora is a Gram-positive bacterium with a wide geographical distribution; it can be found in the soil, mangrove sediments, and freshwater and marine ecosistems.Unexpectedly, a high number of plant-cell wall degrading enzymes were also detected, a trait usually found only in pathogenic bacteria.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Microbiología y Genética, Universidad de Salamanca Salamanca, Spain.

ABSTRACT
For a long time, it was believed that a healthy plant did not harbor any microorganisms within its tissues, as these were often considered detrimental for the plant. In the last three decades, the numbers of studies on plant microbe-interactions has led to a change in our view and we now know that many of these invisible partners are essential for the overall welfare of the plant. The application of Next Generation Sequencing techniques is a powerful tool that has permitted the detection and identification of microbial communities in healthy plants. Among the new plant microbe interactions recently reported several actinobacteria such as Micromonospora are included. Micromonospora is a Gram-positive bacterium with a wide geographical distribution; it can be found in the soil, mangrove sediments, and freshwater and marine ecosistems. In the last years our group has focused on the isolation of Micromonospora strains from nitrogen fixing nodules of both leguminous and actinorhizal plants and reported for the first time its wide distribution in nitrogen fixing nodules of both types of plants. These studies have shown how this microoganism had been largely overlooked in this niche due to its slow growth. Surprisingly, the genetic diversity of Micromonospora strains isolated from nodules is very high and several new species have been described. The current data indicate that Micromonospora saelicesensis is the most frequently isolated species from the nodular tissues of both leguminous and actinorhizal plants. Further studies have also been carried out to confirm the presence of Micromonospora inside the nodule tissues, mainly by specific in situ hybridization. The information derived from the genome of the model strain, Micromonospora lupini, Lupac 08, has provided useful information as to how this bacterium may relate with its host plant. Several strategies potentially necessary for Micromonospora to thrive in the soil, a highly competitive, and rough environment, and as an endophytic bacterium with the capacity to colonize the internal plant tissues which are protected from the invasion of other soil microbes were identified. The genome data also revealed the potential of M. lupini Lupac 08 as a plant growth promoting bacterium. Several loci involved in plant growth promotion features such as the production of siderophores, phytohormones, and the degradation of chitin (biocontrol) were also located on the genome and the functionality of these genes was confirmed in the laboratory. In addition, when several host plants species were inoculated with Micromonospora strains, the plant growth enhancing effect was evident under greenhouse conditions. Unexpectedly, a high number of plant-cell wall degrading enzymes were also detected, a trait usually found only in pathogenic bacteria. Thus, Micromonospora can be added to the list of new plant-microbe interactions. The current data indicate that this microorganism may have an important application in agriculture and other biotechnological processes. The available information is promising but limited, much research is still needed to determine which is the ecological function of Micromonospora in interaction with nitrogen fixing plants.

No MeSH data available.


Related in: MedlinePlus