ABSTRACT
The sulphate-reducing bacteria (SRB) of genus Desulfovibrio are a group of prokaryotes associated with autism spectrum disorders (ASD). The connection between the elevated numbers of Desulfovibrio in the gut of children with ASD compared with healthy children remains unresolved. A conceivable consequence of SRB overgrowth in the gut is the conversion of bioavailable iron into low-soluble crystalline iron sulphides, causing iron deficiency in the organism. In this study, we report the draft genome sequence and physiological features of the first cultivable isolate from a patient with ASD, Desulfovibrio desulfuricans strain AY5.The capability of the strain to produce crystalline iron sulphides was studied under different pH conditions. The most notable greigite(Fe3S4) and pyrite (FeS2) formation was revealed at pH 6.0, which suggests that the iron loss due to insoluble sulphide formation may occur in the proximal part of the gastrointestinal tract. Strain AY5 was adapted to grow under nitrogen-limiting conditions by N2 fixation. The urease found in the strain's genome may play a role in resistance to acidic pH.
ABSTRACT
The ludwigite Co2FeBO5 has been studied experimentally using 57Fe Mössbauer spectroscopy and theoretically using DFT + GGA calculations. The room-temperature Mössbauer spectra are composed of four quadrupole doublets corresponding to the high-spin Fe3+ ions in octahedral oxygen coordination. All components undergo splitting below 117 K due to the magnetic hyperfine fields. The DFT + GGA calculations performed for three models of Fe ion distributions have revealed that the ground state corresponds to the "Fe4(HS)" model with the high-spin Fe3+ ions located at the M4 site and the high-spin Co2+ ions located at the M1, M2, and M3 sites. A ferrimagnetic ground state, with the Co and Fe magnetic moments being nearly parallel to the b-axis and a total magnetic moment of circa 1.1µB f.u.-1, was found. The other Fe distributions cause an increase in the local octahedral distortions and transformation of the spin state. The calculated quadrupole splitting values are in good agreement with the experimental values obtained by Mössbauer spectroscopy.
