Resistance mechanisms of acid Mn 2+-resistant purple nonsulfur bacteria (PNSB) were investigated to determine their ability to alleviate adverse effects of excess manganese on plant growth and productivity in acid sulfate soils (ASS). PNSB were isolated and selected based on their resistance to acid and manganese. Their resistance mechanisms were assessed on the basis of biosorption, bioaccumulation, and plant growth promoting properties. Six PNSB were selected for their resistance to Mn 2+ in acidic conditions (pH 3.5-5.5). They were identified as Rhodopseudomonas palustris strains TLS12, VNS19, VNS32, VNS62, and VNW95, and Rhodopseudomonas harwoodiae strain TLW42. Under aerobic dark and microaerobic light incubating conditions in aqueous solution at pH 4.25 for 30 min, these strains adsorbed Mn 2+ (1500 mg L −1) more effectively with released exopolymeric substances (EPS) than with their biomass. Under both incubating conditions, bioaccumulation of Mn 2+ diminished in the following order: cell wall, cytoplasm, plasma membrane. Scanning electron microscope-energy dispersive X-ray spectrometry (SEM-EDS) found accumulated manganese (0.30-0.67% of total elements) in bacterial cells caused morphological change in the form of wrinkles and bleb-like features on exterior surfaces. All selected strains under both incubating conditions released NH 4 + by N 2 fixing and PO 4 3− by solubilizing phosphate from various P-sources. Siderophores, 5-aminolevulinic acid (ALA), and indole-3-acetic acid (IAA) were also released and pH increased. The studied strains showed potential as bioremediators that could reduce Mn 2+ toxicity using EPS and effectively release nutrients and plant growth promoting substances to improve cultivation and fertility in acidic conditions.

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Abstract. Research on the stability to determine the critical value of structures is a complex issue but of real significance. Piezoelectric composite plate is one of the structures which have the ability to control the mechanical behaviors under loads. One of the prominent capabilities of this structure is the ability to control its vibration and stability. Using the finite element method (FEM) and construction calculation program in Matlab, the authors analyzed the elastic stability of piezoelectric composite plates under dynamic in-plane loads, taking into account damping properties of the structure. Critical loads and other factors affecting the stability of the plate are investigated.

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