The synthesis of elemental selenium particles by Synechococcus leopoliensis

Abstract

Exposure of Synechococcus leopoliensis to selenite in the light resulted in orange-colored granules associated with the cells. No such particles were made in dark grown cells or when selenite was replaced by selenate. Light and scanning electron microscopy revealed that the particles formed inside the cells. Furthermore, these were easily extracted and shown to be composed of selenium as determined by energy-dispersive X-ray spectroscopy. During selenium particle synthesis there was a concurrent loss of organic pigments in the cyanobacteria. Cells also become heavier as they produced and accumulated particles which were on average 220 nm in diameter and generally spherical in shape. The decline in selenite concentration in the culture media can be accounted for by the formation of cellular elemental selenium (Se(0)) during particle formation, although synthesis of small amounts of other Se compounds cannot be entirely discounted. Photosynthetic activity is required for the formation of Se(0), implicating the involvement of thylakoids. It is possible that an intimate association between the nascent particles and the thylakoids occurred. However, Se(0) granule formation did not occur peripherally between the thylakoid and the cytoplasmic membranes, but inside the thylakoid bands towards the center of the cells. It then appears that the particles are mobilized to the periphery and expelled from the cells, causing irreparable damage to the cell walls.

Response surface design for accumulation of selenium by different lactic acid bacteria

“…Similar SEM images and characteristic energy peaks were also obtained from those cells of Se-enriched St (data not shown). These phenomena suggested that Lb and St reduced toxic selenite to elemental Se, and similar properties and phenomena were found in others studies (Bajaj et al 2012;Hnain et al 2013). A summary from Kielisezek et al showed that there are two mechanisms during the process of selenium bioaccumulation and selenium metabolism in yeast cells: one is extracellular binding by ligands of membrane assembly, and another is intracellular accumulation accompanied with the ions transportation across the cytoplasmic membrane into the cell interior.…”

Speeding up bioproduction of selenium nanoparticles by using Vibrio natriegens as microbial factory

“… Bacteria Selenite tolerance Growth SeNPs size Selenite reduction detection* Reference Bacillus mycoides Sel TE01 25 mM Aerobic 50–400 nm Early-exponential growth phase (5 h) 55 Shewanella sp. HN-41 1 mM Anaerobic 11–20 nm Mid-exponential growth phase (12 h) 54 Stenotrophomonas maltophilia SelTE02 5 mM Aerobic 100–300 nm Early-exponential growth phase (80 h) 69 Rhodopseudomonas palustri s N 8 mM Anaerobic 80–200 nm Stationary growth phase (50 h) 70 Pseudomonas moraviensis 120 mM Aerobic ND Stationary growth phase (12 h) 49 Synechococcus leopoliensis 5 mM Aerobic 174–390 nm Mid-exponential growth phase (24 h) 71 Rhodospirillum rubrum 1.5 mM Anaerobic ND Late-exponential growth phase (70 h) 72 Azoarcus sp. CIB 8 mM Anaerobic 88 ± 40 nm Stationary growth phase (48 h) 53 Pseudomonas putida KT2440 10 mM Aerobic 100–500 nm Mid-exponential growth phase (12 h) 48 Vibrio natriegens 100 mM Aerobic 100–400 nm Early-exponential growth phase (3 h) This work * Time required to detect selenite reduction in the cell culture is indicated in brackets.…”

Green synthesis of selenium nanoparticles using<em> Acinetobacter</em> sp. SW30: optimization, characterization and its anticancer activity in breast cancer cells

“…HN-41 and Lactobacillus sp. 35,36 Streptomyces bikiniensis can synthesize nanorods of size 17 nm. 37 It was observed that during the period of incubation, shape of elemental Se changed from spherical to rod-like structure.…”

“…and Bacillus licheniformis JS2. 35,42 The carbonyl groups from amino acids can bind strongly to metals, and hence, they can form a coat around NPs to prevent agglomeration. 35 …”