Purification of an alpha amylase from Aspergillus flavus NSH9 and molecular characterization of its nucleotide gene sequence

In this study, an alpha-amylase enzyme from a locally isolated Aspergillus flavus NSH9 was purified and characterized. The extracellular α-amylase was purified by ammonium sulfate precipitation and anion-exchange chromatography at a final yield of 2.55-fold and recovery of 11.73%. The molecular mass of the purified α-amylase was estimated to be 54 kDa using SDS-PAGE and the enzyme exhibited optimal catalytic activity at pH 5.0 and temperature of 50 °C. The enzyme was also thermally stable at 50 °C, with 87% residual activity after 60 min. As a metalloenzymes containing calcium, the purified α-amylase showed significantly increased enzyme activity in the presence of Ca2+ ions. Further gene isolation and characterization shows that the α-amylase gene of A. flavus NSH9 contained eight introns and an open reading frame that encodes for 499 amino acids with the first 21 amino acids presumed to be a signal peptide. Analysis of the deduced peptide sequence showed the presence of three conserved catalytic residues of α-amylase, two Ca2+-binding sites, seven conserved peptide sequences, and several other properties that indicates the protein belongs to glycosyl hydrolase family 13 capable of acting on α-1,4-bonds only. Based on sequence similarity, the deduced peptide sequence of A. flavus NSH9 α-amylase was also found to carry two potential surface/secondary-binding site (SBS) residues (Trp 237 and Tyr 409) that might be playing crucial roles in both the enzyme activity and also the binding of starch granules. © 2018, Springer-Verlag GmbH Germany, part of Springer Nature

Antimicrobial potential of wild edible herbaceous species

Natural products, either as pure compounds or as standardized extracts, provide unlimited opportunities to control microbial growth, owing to their chemical composition and diversity. Many herb and spice extracts possess antimicrobial activity against a range of bacteria, yeast, and moulds. Because of their antimicrobial properties, they could be very useful, either as food preservatives or as natural biopesticides. In particular, extracts from wild edible herbaceous species are rich in phenolic compounds. A wide variety of phenolics derived from herbs and spices possesses potent biological activities contributing to their effect against spoilage microorganisms. Many studies have pointed out the antimicrobial properties of certain classes of phenolic compounds, such as hydroxybenzoic, coumaric, and caffeic acid derivatives, flavonoids and coumarins, catechin, epicatechin, proanthocyanidins, and tannins. Moreover, some authors studied the relationship between molecular structure and antimicrobial activity of some phenolic compounds. The antimicrobial activity of polyphenols is principally due to inhibition of some important cellular functions (nucleic acid synthesis, cytoplasmatic membrane functionality, etc.) and to disruption of membrane integrity with consequent leakage of cellular contents. This chapter reviews the most important phenol-rich wild edible herbaceous species known within the Mediterranean area, highlighting the relationship between phenolic composition and antimicrobial activity of their extracts. Moreover, the problem of standardization and safety of plant extracts is analyzed in the light of the latest literature

The rhizosphere: Molecular interactions between microorganisms and roots.

The rhizosphere has a large impact on plant performance in several ways. A stand-specific, more or less high diversity of microorganisms not only supports the plant in the acquisition of water and nutrients, but also modulates its ability to cope with pathogens. This diversity, however, has to be maintained and thus causes a considerable drain of photoassimilates, which are then not available for shoot development. In this chapter, we try to explain why the considerable allocation of carbon to the root system is a “wise” decision by the plant. We thus focus on the function of root-associated bacteria and their relevance for plant growth and development of disease resistance, and deliver data on the molecular basis of the root–fungus symbiosis (mycorrhiza)