Paulo Teixeira Lacava

Isolation and enzyme bioprospection of endophytic bacteria associated with plants of Brazilian mangrove ecosystem.

The mangrove ecosystem is a coastal tropical biome located in the transition zone between land and sea that is characterized by periodic flooding, which confers unique and specific environmental conditions on this biome. In these ecosystems, the vegetation is dominated by a particular group of plant species that provide a unique environment harboring diverse groups of microorganisms, including the endophytic microorganisms that are the focus of this study. Because of their intimate association with plants, endophytic microorganisms could be explored for biotechnologically significant products, such as enzymes, proteins, antibiotics and others. Here, we isolated endophytic microorganisms from two mangrove species, Rhizophora mangle and Avicennia nitida, that are found in streams in two mangrove systems in Bertioga and Cananéia, Brazil. Bacillus was the most frequently isolated genus, comprising 42% of the species isolated from Cananéia and 28% of the species from Bertioga. However, other common endophytic genera such as Pantoea, Curtobacterium and Enterobacter were also found. After identifying the isolates, the bacterial communities were evaluated for enzyme production. Protease activity was observed in 75% of the isolates, while endoglucanase activity occurred in 62% of the isolates. Bacillus showed the highest activity rates for amylase and esterase and endoglucanase. To our knowledge, this is the first reported diversity analysis performed on endophytic bacteria obtained from the branches of mangrove trees and the first overview of the specific enzymes produced by different bacterial genera. This work contributes to our knowledge of the microorganisms and enzymes present in mangrove ecosystems.

Endophytic Bacteria: A Biotechnological Potential in Agrobiology System

Endophytes are microorganisms that inhabit the interior of plant tissues without causing harm to the host. This definition includes internal colonists with apparently neutral behavior as well as symbionts. It also includes bacteria that migrate back and forth between the surface and the inside of the plant during their endophytic phase. The utilization of endophytic bacteria for biotechnological purposes has increased recently, especially in pest and disease control and in plant growth promotion. Endophytic bacteria promote plant growth function in three different ways: they synthesize particular compounds for the plants, facilitate the uptake of certain nutrients from the soil, and control or prevent diseases (biological control). Growth promotion mediated by endophytic bacteria includes several mechanisms: the production of vital enzymes; the production of hormones such as auxin (indole acetic acid [IAA]); symbiotic nitrogen fixation; antagonism against phytopathogens caused by the production of siderophores, chitinases, or antibiotics; and the solubilization and mineralization of nutrients, particularly mineral phosphates. Exploitation of the interactions between endophytes and plants can promote plant health and play a significant role in low-input sustainable agriculture for both food and nonfood crops. An understanding of the mechanisms enabling these endophytic bacteria to interact with plants is essential to achieve the biotechnological potential of these microorganisms.

Biological Control of Insect-Pest and Diseases by Endophytes

The natural and biological control of insect-pests and diseases affecting cultivated plants has gained much attention in the past decades as a way of reducing the use of pesticides in agriculture. Biocontrol has been frequently used in tropical countries, such as Brazil, and it is supported by the development of local basic and applied research. In this context, tropical endophytes have attracted special attention to develop their roles to control of pest insect and plant diseases. Endophytic symbiotic microorganisms are defined in different ways and a recent definition includes all of the culturable microorganisms that inhabit inner parts of plant tissues causing no harm to their hosts. They can be divided in two groups: those that do not generate external structures from the host and those able to develop external structures such as nodules of N2 fixing bacteria and mycorrhizal fungi. Endophytes have important roles in the plant host protection, acting against predators and pathogens. They protect host plants against herbivores such as cattle and pest insect. They also may increase plant resistance to pathogens that produce antimicrobial agents and plant-growth hormones and have other effects countering biotic and abiotic stresses. Endophytic microorganisms were first studied in plants in temperate regions but more recently have been also studied in plants from tropical regions. In this chapter, we focus on examples of endophytic bacteria and fungi, especially those that may control pest insects and plant diseases by antagonistic effects, production of enzymes, or introduction of heterologous genes by recombinant DNA technology.

The diversity of citrus endophytic bacteria and their interactions with Xylella fastidiosa and host plants

Abstract The bacterium Xylella fastidiosa is the causal agent of citrus variegated chlorosis (CVC) and has been associated with important losses in commercial orchards of all sweet orange [Citrus sinensis (L.)] cultivars. The development of this disease depends on the environmental conditions, including the endophytic microbial community associated with the host plant. Previous studies have shown that X. fastidiosa interacts with the endophytic community in xylem vessels as well as in the insect vector, resulting in a lower bacterial population and reduced CVC symptoms. The citrus endophytic bacterium Methylobacterium mesophilicum can trigger X. fastidiosa response in vitro, which results in reduced growth and induction of genes associated with energy production, stress, transport, and motility, indicating that X. fastidiosa has an adaptive response to M. mesophilicum. Although this response may result in reduced CVC symptoms, the colonization rate of the endophytic bacteria should be considered in studies that intend to use this endophyte to suppress CVC disease. Symbiotic control is a new strategy that uses symbiotic endophytes as biological control agents to antagonize or displace pathogens. Candidate endophytes for symbiotic control of CVC must occupy the xylem of host plants and attach to the precibarium of sharpshooter insects to access the pathogen. In the present review, we focus on interactions between endophytic bacteria from sweet orange plants and X. fastidiosa, especially those that may be candidates for control of CVC.

Screening of tropically derived, multi-trait plant growth- promoting rhizobacteria and evaluation of corn and soybean colonization ability

The present study assessed the plant growth-promoting (PGP) traits and diversity of culturable rhizobacteria associated with guarana (Paullinia cupana), a typical tropical plant. Ninety-six bacteria were isolated, subjected to biochemical tests, and identified by partial or total 16S rDNA sequencing. Proteobacteria and Firmicutes were the dominant rhizospheric phyla found, and Burkholderia and Bacillus were the most abundant genera. Thirteen strains exhibited the four PGP traits evaluated, and most of them belonged to the genus Burkholderia. Two multi-trait PGP strains, RZ2MS9 (Bacillus sp.) and RZ2MS16 (Burkholderia ambifaria), expressively promoted corn and soybean growth under greenhouse conditions. Compared to the non-inoculated control, increases in corn root dry weight of 247.8 and 136.9% were obtained with RZ2MS9 and RZ2MS16 inoculation, respectively, at 60days after seeding. The dry weights of corn and soybean shoots were significantly higher than those of non-inoculated plants, showing increases of more than 47% for both strains and crops. However, soybean root dry weight did not increased after bacterial inoculation with either strain. The colonization behavior of RZ2MS16 was assessed using GFP-labeling combined with fluorescence microscopy and a cultivation-based approach for quantification. RZ2MS16:gfp was able to colonize the roots and shoots of corn and soybean, revealing an endophytic behavior.

Diversity and Biotechnological Potential of Endophytic Microorganisms Associated with Tropical Mangrove Forests

Mangroves are typical tropical ecosystems situated between land and sea. These biological communities are frequently found in tropical and subtropical areas and occupy approximately 18.1 million hectares of the planet. Endophytic microorganisms inhabit the internal tissues of plants without generating negative effects and represent an extensive source of promising natural products. Endophytes protect the plant host against predators and pathogens, including cattle and insect pests. That may also increase the resistance of plants against biotic and abiotic stresses and produce plant growth hormones, antibiotics, enzymes, and many other compounds of biotechnological interest. Endophytic microorganisms produce antibiotics that enable their survival in competitive habitats with other microorganisms protecting the host against other bacterial and fungal pathogens. The biochemical versatility and diversity of rare microorganisms suggest that many active compounds remain unknown. Endophytes from mangroves open up new areas of potential biotechnological exploitation; thus, isolating and cultivating these organisms are of great importance. The production of bioactive natural compounds that are important for both pharmaceutical and agricultural fields is widespread among endophytes. The great biodiversity observed in the mangrove ecosystem reinforces the importance of studying endophytic microorganisms, particularly the isolation of new compounds.

Role of Endophytic Actinomycetes in Crop Protection: Plant Growth Promotion and Biological Control

Endophytes are microorganisms that inhabit the interior of plant tissues without causing apparent disease in the host plant. The utilization of endophytic microorganisms for agricultural purposes has increased recently, especially in the biological control of insect-pest and plant disease and in plant growth promotion. Research has shown that many endophytic actinomycetes are beneficial to host plants with regard to the biological control of phytopathogens and plant growth promotion. Endophytic actinomycetes may promote plant growth by a combination of mechanisms, such as the solubilization of nutrients and the production of growth hormones and enzymes. Because actinomycetes are able to produce spores, a dissemination structure that offers resistance to many adverse conditions. These actinobacteria could be used for the formulation of novel bioinoculants composed of spores and/or mycelium. An understanding of the mechanisms enabling these endophytes to interact with host is important for realizing the potential of these microorganisms in agriculture production.

Endophytic Microorganisms of the Tropical Savannah: A Promising Source of Bioactive Molecules

The Brazilian tropical savannah, known as the “Cerrado”, is comprised of rich and characteristic flora, which makes it one of the 25 most important terrestrial biodiversity hotspots on the planet. This ecosystem is characterized by seasonal weather with annual precipitation that varies between 1200 and 1800 mm and a dry season that occurs during 5–6 months a year. This Brazilian savannah is a typical mosaic biome characterized by plants that can be endemic to this niche and several plant species that have medicinal properties and great pharmaceutical relevance. Although interest has increased in the microbial biodiversity associated with medicinal plants, the diversity, taxonomic composition, and biotechnological potential of endophytic microorganisms associated with these tropical plants from the savannah remain unclear. Plant-associated microorganisms such as endophytes are subjected to constant metabolic and environmental interactions, and these organisms should produce more secondary metabolites. These molecules are characterized by their diverse chemical structures and may be of use due to the wide range of their bioactivity against pathogens. The native plants of the Brazilian savannah are commonly used to treat skin diseases, ulcers, anemia, diabetes, malaria, inflammatory reactions, and hepatic diseases, and this medicinal flora has been used as folk medicine by different people as an alternative to high-priced pharmaceutical drugs. However, only a few of the medicinal Brazilian plants have been studied as a source of bioactive endophytic microbial communities. Several endophytes are important for microbial activities such as antibiotic capability against Gram-positive and Gram-negative bacteria, antifungal, antibiotic resistance, enzyme production, antitumor activity, and anti-Leishimania activity. The exploration of endophytes from new host hosts is important for assessing the potential of these microorganisms in different application areas and for emphasizing the potential of natural compounds that can be used in clinics and the pharmaceutical industry.

Mangrove endophyte promotes reforestation tree (Acacia polyphylla) growth

Mangroves are ecosystems located in the transition zone between land and sea that serve as a potential source of biotechnological resources. Brazils extensive coast contains one of the largest mangrove forests in the world (encompassing an area of 25,000 km2 along all the coast). Endophytic bacteria were isolated from the following three plant species: Rhizophora mangle, Laguncularia racemosa and Avicennia nitida. A large number of these isolates, 115 in total, were evaluated for their ability to fix nitrogen and solubilize phosphorous. Bacteria that tested positive for both of these tests were examined further to determine their level of indole acetic acid production. Two strains with high indole acetic acid production were selected for use as inoculants for reforestation trees, and then the growth of the plants was evaluated under field conditions. The bacterium Pseudomonas fluorescens (strain MCR1.10) had a low phosphorus solubilization index, while this index was higher in the other strain used, Enterobacter sp. (strain MCR1.48). We used the reforestation tree Acacia polyphylla. The results indicate that inoculation with the MCR1.48 endophyte increases Acacia polyphylla shoot dry mass, demonstrating that this strain effectively promotes the plants growth and fitness, which can be used in the seedling production of this tree. Therefore, we successfully screened the biotechnological potential of endophyte isolates from mangrove, with a focus on plant growth promotion, and selected a strain able to provide limited nutrients and hormones for in plant growth.