Evidence for ferritin as dominant iron-bearing species in the rhizobacterium Azospirillum brasilense Sp7 provided by low-temperature/in-field Mössbauer spectroscopy

Abstract

For the ubiquitous diazotrophic rhizobacterium Azospirillum brasilense, which has been attracting the attention of researchers worldwide for the last 35 years owing to its significant agrobiotechnological and phytostimulating potential, the data on iron acquisition and its chemical speciation in cells are scarce. In this work, for the first time for azospirilla, low-temperature (at 80 K, 5 K, as well as at 2 K without and with an external magnetic field of 5 T) transmission Mössbauer spectroscopic studies were performed for lyophilised biomass of A. brasilense (wild-type strain Sp7 grown with (57)Fe(III) nitrilotriacetate complex as the sole source of iron) to enable quantitative chemical speciation analysis of the intracellular iron. In the Mössbauer spectrum at 80 K, a broadened quadrupole doublet of high-spin iron(III) was observed with a few percent of a high-spin iron(II) contribution. In the spectrum measured at 5 K, a dominant magnetically split component appeared with the parameters typical of ferritin species from other bacteria, together with a quadrupole doublet of a superparamagnetic iron(III) component and a similarly small contribution from the high-spin iron(II) component. The Mössbauer spectra recorded at 2 K (with or without a 5 T external field) confirmed the assignment of ferritin species. About 20% of total Fe in the dry cells of A. brasilense strain Sp7 were present in iron(III) forms superparamagnetic at both 5 and 2 K, i.e. either different from ferritin cores or as ferritin components with very small particle sizes.

Studies Using Mutant Strains of Azospirillum brasilense Reveal That Atmospheric Nitrogen Fixation and Auxin Production Are Light Dependent Processes

“…Similarly, wild-type Sp7 A. brasilense bacteria reared under the same conditions reduced 22% of the assimilated Fe 3+ -to-Fe 2+ [ 50 ]. These Mössbauer studies suggested that cellular Fe 3+ was stored in ferritin-like components which was verified in other work [ 49 , 51 ]. Furthermore, these studies showed that Fe 2+ existed in highly coordinated forms [ 48 , 50 ].…”

“…Upon surveying the early literature that addressed metal nutrient uptake and metabolic transformation within live cells of rhizospheric microorganisms, and particularly Azospirilla , we found the number of published works scarce [ 43 , 44 , 45 , 46 ]. It was not until later applications of Mössbauer spectroscopy (reviewed in [ 47 ]) that a greater understanding of microbial demands for iron came to light [ 48 , 49 , 50 , 51 , 52 ]. In this collection, studies using wild-type Sp245 A. brasilense grown aeroponically in cultures containing 57 Fe 3+ -nitrilotriacetate complex showed that live cells reduced 33% of the assimilated Fe 3+ -to-Fe 2+ over an 18 h period of growth [ 48 ].…”

The Collection of Rhizosphere Microorganisms: its importance for the study of associative plant-bacterium interactions

“…By using glutamine synthetase isolated from A. brasilense Sp245 cells as an example, the possibility of applying nuclear gamma resonance spectroscopy ( 57 Co nuclei) to the examination of the structural organization of metal cation binding sites in active centers of enzymes was shown . For the first time in relation to Azospirillum bacteria, the assimilation of iron and the composition and structure of iron-containing cellular components were studied (Kovács et al, 2016), and so were the interaction and metabolic transformations of cobalt ions by A. brasilense cultures .…”

Temperature Field Analysis of High-Speed Bearings Considering Frictional Heat and Interactive Effects

“…If the bearing friction torque is too large, the temperature of the bearing will increase significantly, the lubrication performance of non-circulating grease will be greatly reduced, relative thermal displacement will occur inside the bearing components, and it is easy to cause surface burns on internal components, leading to bearing failure, damage, or even premature scrapping [8][9][10][11][12][13]. The temperature of the bearing has a significant impact on its service life and flexibility, and the deformation of components caused by friction factors also seriously affects the accuracy and stability of machined parts [14][15][16][17][18][19][20]. Therefore, it is more important to analyze the temperature field of bearings in high-speed electric spindle machining applications.…”