[Show abstract][Hide abstract] ABSTRACT: AIMS: The aim of this work was to clarify the mechanism of monounsaturated fatty acid (MUFA) synthesis in Bradyrhizobium TAL1000 and the effect of high temperature on this process. METHODS AND RESULTS: Bradyrhizobium TAL1000 was exposed to a high growth temperature and heat shock, and fatty acid composition and synthesis were tested. To determine the presence of a possible desaturase, a gene was identify and overexpressed in Escherichia coli. The desaturase expression was detected by RT-PCR and Western blotting. In B. TAL1000, an aerobic mechanism for MUFA synthesis was detected. Desaturation was decreased by high growth temperature and by heat shock. Two hours of exposure to 37°C were required for the change in MUFA levels. A potential ∆9 desaturase gene was identified and successfully expressed in E. coli. A high growth temperature and not heat shock reduced transcript and protein desaturase levels in rhizobial strain. CONCLUSIONS: In B. TAL1000, the anaerobic MUFA biosynthetic pathway is supplemented by an aerobic mechanism mediated by desaturase and is down-regulated by temperature to maintain membrane fluidity under stressful conditions. SIGNIFICANCE AND IMPACT OF THE STUDY: This knowledge will be useful for developing strategies to improve a sustainable practice of this bacterium under stress and to enhance the bioprocess for the inoculants' manufacture.
Journal of Applied Microbiology 03/2013; · 2.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The rhizosphere is a multiple interface between soils, plant roots, microbes and fauna, where different biological components
interact strongly. Rhizosphere
interactions are based on complex exchanges that take place around plant roots. Beneficial, detrimental and neutral relationships
between plant roots and microorganisms are all regulated by complex molecular signalling. Plants exude a variety of organic
compounds (e.g. carbohydrates, carboxylic acids, phenolics, amino acids, flavonoids) as well as inorganic ions (protons and
other ions) into the rhizosphere which change the chemistry and biology of the root microenvironment. All chemical compounds
secreted by plants are collectively named rhizodepositions. In the rhizosphere, bacteria that exert beneficial effects on
plant development are referred to as plant growth-promoting rhizobacteria (PGPR) because their application is often associated
with increased rates of plant growth. On the other hand, although many technologies have been used in the improvement of stress
tolerance in plants, fewer reports have been published on how PGPR can exert tolerance to salt, drought or heavy metals. In
addition, the industrial use and technological application of compounds from plants and rhizobacteria are required to be successful
in attaining sustainable microbial-based agrotechnologies. Among crops, legumes are a good source of starch, dietary fibre,
protein and minerals. It has long been recognized that legumes are functional foods that promote good health and have therapeutic
properties. This chapter shows the significance of some biochemical and biological compounds derived from legumes and rhizobacteria
with potential in biotechnology.
[Show abstract][Hide abstract] ABSTRACT: Growth and survival of bacteria depend on homeostasis of membrane lipids, and the capacity to adjust lipid composition to adapt to various environmental stresses. Membrane fluidity is regulated in part by the ratio of unsaturated to saturated fatty acids present in membrane lipids. Here, we studied the effects of high growth temperature and salinity (NaCl) stress, separately or in combination, on fatty acids composition and de novo synthesis in two peanut-nodulating Bradyrhizobium strains (fast-growing TAL1000 and slow-growing SEMIA6144). Both strains contained the fatty acids palmitic, stearic, and cis-vaccenic + oleic. TAL1000 also contained eicosatrienoic acid and cyclopropane fatty acid. The most striking change, in both strains, was a decreased percentage of cis-vaccenic + oleic (≥ 80% for TAL1000), and an associated increase in saturated fatty acids, under high growth temperature or combined conditions. Cyclopropane fatty acid was significantly increased in TAL1000 under the above conditions. De novo synthesis of fatty acids was shifted to the synthesis of a higher proportion of saturated fatty acids under all tested conditions, but to a lesser degree for SEMIA6144 compared to TAL1000. The major adaptive response of these rhizobial strains to increased temperature and salinity was an altered degree of fatty acid unsaturation, to maintain the normal physical state of membrane lipids.
[Show abstract][Hide abstract] ABSTRACT: The rhizosphere is the volume of soil under the influence of plants roots, where very important and intensive microbe–plant
interactions take place. These interactions can both significantly influence plant growth and crop yields and have biotechnological
applications. The rhizosphere harbors a diverse community of microorganisms that interact and compete with each other and
with the plant root. The activity of some of the members of this community affects the growth and the physiology of the others,
as well as the physical and chemical properties of the soil. Among all these interactions, those resulting in symbiotic and
non-symbiotic nitrogen fixation are considerably important. In recent years, the use of bacteria (rhizobacteria) to promote
plant growth has increased in several regions of the world and has acquired relevant importance in developing countries that
are the producers of raw materials for food. Rhizobacteria can affect plant growth by producing and releasing secondary metabolites,
which either decrease or prevent the deleterious effects of phytopathogenic organisms in the rhizosphere, and/or by facilitating
the availability and uptake of certain nutrients from the root environment. Significant increases in the growth and yield
of agriculturally important crops in response to inoculation with rhizobacteria have been reported. This practical application
of plant growth-promoting rhizobacteria is the main focus of this chapter.
[Show abstract][Hide abstract] ABSTRACT: The legume–rhizobia symbiosis is considered the most important nitrogen-fixing interaction from an agricultural point of view.
However, biotic and abiotic factors can modify critical parameters of both the legumes and the rhizobia. These changes may
lead to differences in the molecular dialogue, consequently reducing the symbiotic effectiveness. Therefore, optimal performance
of the N-fixing symbiosis will be guaranteed by selection of both symbiotic partners for adaptation to the target environment.
The symbiotic process can be negatively affected by many other rhizosphere interactions, resulting in important ecological,
economic, and nutritional losses. The application of agricultural techniques that are friendly with the environment, based
on the use of plant growth promoting rhizobacteria (PGPR), can increase the efficiency of the symbiotic process. The use of
these beneficial microorganisms could reduce the use of polluting chemicals allowing sustainable production of legumes. Co-inoculations
of appropriate rhizobia together with PGPR may profoundly increase the crop yield by different mechanisms. The negative effects
of environmental stresses on the legume–rhizobia symbiosis may further be significantly diminished by applying mixtures of
rhizobia and PGPR.
[Show abstract][Hide abstract] ABSTRACT: Phosphatidylcholine, the major phospholipid in eukaryotes, is found in rhizobia and in many other bacteria interacting with eukaryotic hosts. Phosphatidylcholine has been shown to be required for a successful interaction of Bradyrhizobium japonicum USDA 110 with soybean roots. Our aim was to study the role of bacterial phosphatidylcholine in the Bradyrhizobium-peanut (Arachis hypogaea) symbiosis. Phospholipid N-methyltransferase (Pmt) and minor phosphatidylcholine synthase (Pcs) activities were detected in crude extracts of the peanut-nodulating strain Bradyrhizobium sp. SEMIA 6144. Our results suggest that phosphatidylcholine formation in Bradyrhizobium sp. SEMIA 6144 is mainly due to the phospholipid methylation pathway. Southern blot analysis using pmt- and pcs-probes of B. japonicum USDA 110 revealed a pcs and multiple pmt homologues in Bradyrhizobium sp. SEMIA 6144. A pmtA knockout mutant was constructed in Bradyrhizobium sp. SEMIA 6144 that showed a 50% decrease in the phosphatidylcholine content in comparison with the wild-type strain. The mutant was severely affected in motility and cell size, but formed wild-type-like nodules on its host plant. However, in coinoculation experiments, the pmtA-deficient mutant was less competitive than the wild type, suggesting that wild-type levels of phosphatidylcholine are required for full competitivity of Bradyrhizobium in symbiosis with peanut plants.
[Show abstract][Hide abstract] ABSTRACT: Phospholipids provide the membrane with its barrier function and play a role in a variety of processes in the bacterial cell, as responding to environmental changes. The aim of the present study was to characterize the physiological and metabolic response of Bradyrhizobium SEMIA 6144 to saline and temperature stress. This study provides metabolic and compositional evidence that nodulating peanut Bradyrhizobium SEMIA 6144 is able to synthesize fatty acids, to incorporate them into its phospholipids (PL), and then modify them in response to stress conditions such as temperature and salinity. The fatty acids were formed from [1-(14)C]acetate and mostly incorporated in PL (95%). Phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), and cardiolipin (CL) were found to be the major phospholipids in the bacteria analyzed. The amount and the labeling of each individual PL was increased by NaCl, while they were decreased by temperature stress. The amount of PC, PE, and PG under the combined stresses decreased, as in the temperature effect. The results indicate that synthesized PL of Bradyrhizobium SEMIA 6144 are modified under the tested conditions. Because in all conditions tested the PC amount was always modified and PC was the major PL, we suggest that this PL may be involved in the bacteria response to environmental conditions.
Current Microbiology 02/2007; 54(1):31-5. · 1.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The effects of saline and osmotic stress on four peanut rhizobia, plant growth and symbiotic N2-fixation inArachis hypogaea were studied. Abiotic stress was applied by adding either 100 mM NaCl or 20 mM PEG6000. At the rhizobial level,Bradyrhizobium ATCC10317 and TAL1000 showed stronger tolerance to stress than TAL1371 and SEMIA6144. The effect of salinity on the bacterium-plant
association was studied by using the variety Blanco Manfredi M68. In the absence of stresses, all the strains induced a significantly
higher number of nodules on the roots, although TAL1371 and SEMIA6144 were more effective. Both stresses affected the interaction
process, while TALl371 was the best partner.