Background: Amylases are among the most important enzymes which are of great significance for biotechnology and have almost completely replaced chemical hydrolysis of starch in the starch processing industry. The present study was concerned with the production and optimization of extracellular α-amylase from Bacillus sp. NRC22017. Results: The effect of various fermentation conditions on α-amylase production through shake-flask culture was investigated. Bacterial strain produces α-amylase was isolated from water in Wadi El-Natron. Based on microbiological, biochemical tests, and 16S rRNA gene sequences, the isolate was identified as Bacillus sp. NRC22017 and was later used for further studies. Maximum yield of α-amylase is 15.15 ± 0.47 U/ml from Bacillus sp. NRC22017; this strain is characterized with high temperature and high salinity in cultivated culture, and achieved maximum yield of α-amylase at pH 6.0 with inoculum size of 500 μl at 45°C and aerobically incubation period of 72 h. The optimum volume of the fermentation medium was found to be 20 ml in 100 ml Erlenmeyer flask; the best starch and meat extract plus peptone concentration that provided the highest enzyme production from Bacillus sp. NRC22017 were found to be 2% and 1.05% (w/v) respectively. Conclusion: Enzyme production was higher after optimizing the production conditions as compared to the basal medium.

Microbial exopolysaccharides (EPSs) extracted from lactic acid bacteria (LAB) are generally recognized as safe. They have earned popularity in recent years because of their exceptional biological features. Therefore, the present study main focus was to study EPS-production from probiotic LAB and to investigate their antioxidant and burn wound healing efficacy. Seventeen LAB were isolated from different food samples. All of them showed EPS-producing abilities ranging from 1.75 ± 0.05 to 4.32 ± 0.12 g/l. RO30 isolate (from Romi cheese) was chosen, due to its ability to produce the highest EPS yield (4.23 ± 0.12 g/l). The 16S rDNA sequencing showed it belonged to the Lactiplantibacillus plantarum group and was further identified as L. plantarum RO30 with accession number OL757866. It displayed well in vitro probiotic properties. REPS was extracted and characterized. The existence of COO−, OH and amide groups corresponding to typical EPSs was confirmed via FTIR. It was constituted of glucuronic acid, mannose, glucose, and arabinose in a molar ratio of 2.2:0.1:0.5:0.1, respectively. The average molecular weight was 4.96 × 104 g/mol. In vitro antioxidant assays showed that the REPS possesses a DPPH radical scavenging ability of 43.60% at 5 mg/ml, reducing power of 1.108 at 10 mg/ml, and iron chelation activity of 72.49% and 89.78% at 5 mg/ml and 10 mg/ml, respectively. The healing efficacy of REPS on burn wound models in albino Wistar rats showed that REPS at 0.5% (w/w) concentration stimulated the process of healing in burn areas. The results suggested that REPS might be useful as a burn wound healing agent.

α-Amylase biosynthesis was illustrated under stress circumstances of high temperature and high salinity in aerobically cultivated culture of a newly isolated moderately thermophilic bacterium of spore-forming Bacillus sp. NRC12017 in medium containing starch, peptone and yeast extract. Maximum yield (18.41 U/ml) was took place at pH 6.5 with 200 µl inoculum size at 45°C and an incubation time of 3 days. The ideal volume of the fermentation broth was found to be 15 ml in 100 ml Erlenmeyer flask, supplementation of starch at 2.5% and peptone plus yeast extract at 0.7% brought about the greatest production of α-amylase. Two fractions of α-amylase activities, designated FIII and FIV, were refined from culture filtrate utilizing ammonium sulfate (60 and 80%) and showed the main band at 30 KDa. Both fractions had the highest activity at 250 µl starch in a reaction mixture and pH 6.0-7.0. FIII and FIV showed that a temperature of 50 and 55°C and a reaction time of 20 and 30 min were the best available conditions for their activities, respectively, both fractions were stable up to 65°C and the activity was decreased drastically to 3.22 and 3.26 % when heated at 70°C. Concerning pH stability, a broad range of pH stability (5.0-11.0) was obtained by FIII and FIV.

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