Polyhydroxyalkanoates are biodegradable polymer materials that accumulate in numerous bacteria. The polyhydroxybutyrate is the most common type of polyhydroxyalkanoates, which potentially serves as precursor for bioplastic production. The most extensively studied polyhydroxybutyrate producing bacteria is Cupriavidus necator due to its capability to accumulate large amounts of this biopolymer in simple culture medium. Accumulation of polyhydroxyalkanoates granules in the cytoplasm of C. necator significantly depended on pH, aeration, carbon sources, nitrogen sources, and minerals in the culture medium. In the present study, the effect of both nutritional and physical variables on polyhydroxybutyrate production was investigated in order to optimize these conditions. At first, on the basis of one-factor-at-a-time experiments, fructose and ammonium chloride were found to be the most suitable sources of carbon and nitrogen for biopolymer production. Then the most significant factors affecting granules accumulation were recognized as fructose, agitation speed, KH 2 PO 4 , and initial pH using the Plackett-Burman and central composite design. ANOVA analysis showed significant interaction between fructose and agitation speed. After optimization of the medium, compositions for polyhydroxybutyrate production were determined as follows: fructose 35 g/L, KH 2 PO 4 1.75 g/L, MgSO 4 Á7H 2 O 1.2 g/L, citric acid 1.7 g/L, trace element 10 mL/L, initial pH = 7, and agitation speed 175 rpm. Under this optimal culture conditions, the maximum yield of PHB was 7.48 g/L. The present strategies included in this study could be used for PHB production by this bacterium. These results are the highest values of PHB ever obtained from batch culture of C. necator reported so far.

Polyhydroxybutyrate (PHBs) have attracted much attention due to their biodegradability and biocompatibility properties. The main drawback to the commercial production of them is their high cost. The recovery of PHB from bacterial cytoplasm significantly increases total processing costs. Efficient, economical, and environmentfriendly extraction of PHB from cells is required for its industrial production. In the present study, several nonhalogenated organic solvents (ethylene carbonate, dimethyl sulfoxide, dimethyl formamide, hexane, propanol, methanol, and acetic acid) were examined for their efficacy regarding recovery at different temperatures from culture broth containing Cupriavidus necator cells. The highest recovery percentage (98.6%) and product purity (up to 98%) were seen to be those of ethylene carbonate-assisted extraction at 150°C within 60 min of incubation time. Average molecular weight of the recovered PHB (1.3 × 10 6 ) was not significantly affected by the extraction solvent and conditions. The melting point of PHB extracted using ethylene carbonate was measured to be 176.2°C with an enthalpy of fusion of 16.8% and the corresponding degree of crystallinity of 59.2%. NMR and GC analyses confirmed that the extracted biopolymer was PHB. The presented strategy can help researchers to reduce the cost to obtain the final product.

The present study developed an efficient and environmentally friendly method for recovering polyhydroxybutyrate (PHB) from Cupriavidus necator. Several non-halogenated solvents were tested and it was found that butyl acetate and ethyl acetate are powerful solvents for the biopolymer. Testing was performed to examine the effects of temperature (25 °C until temperature below solvent boiling points) and heating incubation time (0-60 min) on the two solvents. Butyl acetate had a higher recovery level (96%) and product purity (up to 99%) than ethyl acetate at 103 °C and a heating incubation time of 30 min. Under these conditions, PHB recorded the highest molecular weight of 1.4 × 10(6) compared with the standard procedure (i.e., recovery using chloroform). The proposed strategy showed that butyl acetate is a good alternative to halogenated solvents such as chloroform for recovery of PHB.

Staphylococcal enterotoxin B, from Staphylococcus aureus (S. aureus), is one of the most potent bacterial superantigens with profound toxic effects on the immune system. It is associated with food poisoning, toxic shock, atopic dermatitis, asthma, and nasal polyps in humans. The current diagnostic methods for staphylococcal enterotoxin are mainly based on traditional monoclonal antibodies which hardly meet the requirements for clinical applications, and hybridoma clones lose their ability to secrete antibodies during time. The present study investigates the development of a novel, highly specific, low-cost, and sensitive nanobody capable of being used in immunoassays for Staphylococcal enterotoxin B (SEB) detection in suspicious foods. For this purpose, Camelus dromedarius was immunized against SEB toxin. After obtaining acceptable titration, a high-quality phage display nanobody library (4 × 10 PFU/ml) was constructed. High-affinity SEB-specific nanobodies were retrieved from constructed libraries. After phage rescue and five round of biopanning, clone screening was performed by phage ELISA. Recombinant nanobodies which were expressed from C7 and C21 clone showed the highest affinity for SEB. The presence of high quality and pure nanobody band at ~ 15 kDa was confirmed by SDS-PAGE and western blotting. The affinity constant which was measured by ELISA was calculated to be around 10 M. The results suggest that the proposed detection method by nanobodies is an alternative diagnostic tool enabling a rapid, inexpensive, and specific detection of the SEB.

RADA 16-I is a synthetic amphiphilic peptide, composed of 16 amino acids, designed to self-assemble in a controlled way into fibrils and higher ordered structures depending on solvent condition. This peptide has many applications in tissue engineering and wound healing. We have studied the cluster formation of four RADA 16-I peptide chains in the presence of different concentrations of NaCl and CaCl 2 as solvents, using all-atom molecular dynamics simulation. Nine independent simulations over 20 ns were performed. The results show that the fastest cluster formation rate occurs in the presence of 0.2 M NaCl following by water. In these simulations cluster formation doesn't occur in the presence of CaCl 2 . It is also found that the cluster formation depends on two solvent-related factors: (a) salt concentration and (b) salt type. The effect of salts may act through changing the compactness and secondary structure of this peptide. In fact NaCl helps each peptide to adopt transitional expanded a-helical conformation in order to induce better interaction sites for self-assembly. The results gave insight into the effect of ionic strength in self-assembly mechanism of RADA 16-I in the bulk solution.Electronic supplementary material The online version of this article (