PowerPoint Contents
Introduction
Polymeric molecules found in the environment such as cellulose, chitin, starch, protein, and nucleic acids are degraded by exoenzymes such as proteases, nucleases, and amylases synthesized by members of the genus Bacillus in order to obtain carbon sources for their metabolic processes. Bacterial membrane-spanning transporters admit biomolecules no larger than 600 to 700 daltons, and high molecular mass molecules must be degraded in order to pass through the bacterial membrane-spanning transporters. Starch is a homopolymer of glucose and is the most important reserve polysaccharide found in plants; casein is the principal protein fraction of milk and contains all essential amino acids; gelatin is a heterogeneous mixture of water-soluble proteins of high average relative molecular mass derived from collagen. Based on proteolytic, lipolytic, and saccharolytic activities of Bacillus species, these organisms have been used to ferment cereal or legume foods to obtain condiments such as Bikalga and dawadawa, used to flavor soups and stews in the African diet. Moreover, inclusion of amylases from Bacillus species in detergents affords advantages such as reduction or replacement of other components that may be harmful to the environment. The hydrolysis test with substrates such as starch, casein, and gelatin have been used mainly for screening of proteolytic and amylolytic activities in Bacillus species used in food microbiology settings, such as selection of Bacillus isolates for starter cultures for cereal or legume foods fermentations.
Figure 1: Starch hydrolysis by Bacillus spp. A) A Bacillus spp. isolated from the environment, plated on starch agar, grown for 24 hours, and flooded with Gram's iodine solution. Iodine reacts with starch to produce a blue-black color. Starch degradation is visible as a clear zone surrounding the microbial growth where bacterial exoenzymes hydrolyzed the starch in the agar. B) Escherichia coli plated on starch agar, grown for 24 hours, and flooded with Gram's iodine. There is no clear zone surrounding the bacterial growth showing that E. coli did not hydrolyze the starch.
Figure 2: Casein hydrolysis by Bacillus species. A) A Bacillus spp. isolated from the environment, plated on casein agar, grown for 24 hours, and flooded with mercuric chloride solution. Casein degradation is visible as a clear zone surrounding the microbial growth where bacterial exoenzymes hydrolyzed the casein in the agar. B) Escherichia coli plated on casein agar, grown for 24 hours, and flooded with mercuric chloride solution. There is no clear zone surrounding the bacterial growth showing that E. coli did not hydrolyze the casein.
Figure 3: Gelatin degradation by Bacillus species. A) A Bacillus spp. isolated from the environment, plated on gelatin agar, grown for 24 hours, and flooded with mercuric chloride solution. Gelatin degradation is visible as a clear zone surrounding the microbial growth where bacterial exoenzymes hydrolyzed the gelatin in the agar. B) Escherichia coli plated on gelatin agar, grown for 24 hours, and flooded with mercuric chloride solution. There is no clear zone surrounding the bacterial growth showing that E. coli did not hydrolyze the gelatin.
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