Production and characterization of naturally occurring antibacterial magnetite nanoparticles from magnetotactic Bacillus sp. MTB17

Antibacterial Activity, GC MS Analysis and In Silico Validation of Bioactive Compound from Endophytic Fungus Lasiodiplodia pseudotheobromae EF-9

Secondary metabolites synthesized by endophytic fungi have garnered significant interest for their broad applications in treating various ailments. In this study involving 20 plant samples, 11 endophytic fungi were isolated and cultured, and Lasiodiplodia pseudotheobromae EF-9, derived from Hibiscus rosa-sinensis, demonstrated greater antibacterial efficacy than the other isolated endophytes. Phylogenetic analyses using 18S rRNA gene confirmed the EF-9 identity as L. pseudotheobromae. Following mass production, the active compound was partially purified using column chromatography. The fraction collected at the 60th min exhibited good antibacterial activity against Bacillus coagulans (MTCC 6735) and Shigella flexneri (ATCC 12022), with an inhibition zone of approximately 20 mm in diameter. UV spectral studies revealed a wide absorption band at 430 nm. High Performance Liquid Chromatography (HPLC) of the active fraction showed a distinct peak with a retention time of 4.216 min at 430 nm. Gas Chromatography-Mass Spectrometry (GC-MS) identified the active compound in the L. pseudotheobromae EF-9 culture broth extract as Bis(2-ethylhexyl) phthalate, which displayed a peak at 16.856 min and covered 66.69 % of the area in the spectral analysis.

Effects of static magnetic field on the sulfate metabolic pathway involved in Magnetospirillum magneticum AMB-1 cell growth and magnetosome formation

AIMS

Magnetotactic bacteria (MTB) can use their unique intracellular magnetosome organelles to swim along the Earth's magnetic field. They play important roles in the biogeochemical cycles of iron and sulfur. Previous studies have shown that the applied magnetic fields could affect the magnetosome formation and antioxidant defense systems in MTB. However, the molecular mechanisms by which magnetic fields affect MTB cells remain unclear. We aim to better understand the dark at 28°C-29°C for 20 h, as shownthe interactions between magnetic fields and cells, and the mechanism of MTB adaptation to magnetic field at molecular levels.

METHODS AND RESULTS

We performed microbiological, transcriptomic, and genetic experiments to analyze the effects of a weak static magnetic field (SMF) exposure on the cell growth and magnetosome formation in the MTB strain Magnetospirillum magneticum AMB-1. The results showed that a 1.5 mT SMF significantly promoted the cell growth but reduced magnetosome formation in AMB-1, compared to the geomagnetic field. Transcriptomic analysis revealed decreased expression of genes primarily involved in the sulfate reduction pathway. Consistently, knockout mutant lacking adenylyl-sulfate kinase CysC did no more react to the SMF and the differences in growth and Cmag disappeared. Together with experimental findings of increased reactive oxidative species in the SMF-treated wild-type strain, we proposed that cysC, as a key gene, can participate in the cell growth and mineralization in AMB-1 by SMF regulation.

CONCLUSIONS

This study suggests that the magnetic field exposure can trigger a bacterial oxidative stress response involved in AMB-1 growth and magnetosome mineralization by regulating the sulfur metabolism pathway. CysC may serve as a pivotal enzyme in mediating sulfur metabolism to synchronize the impact of SMF on both growth and magnetization of AMB-1.