| Procaryotic strain 2-40 is presumptively classified within the genus Alteromonas. It is a periphytic marine bacterium isolated from the Chesapeake Bay, growing on decaying marsh grass, Spartina alterniflora. 2-40 produces many different degradative enzymes, especially carbohydrases including agarase, alginase, amylase, carrageenanase, carboxymethylcellulase, pullulanase, and xylanase. These enzymes allow 2-40 to utilize recalcitrant insoluble carbohydrates of plant, fungal, and bacterial origin. To better understand how organisms such as 2-40 can survive in environments where complex, particulate nutrients predominate, the agarase system was selected for further study.; The 2-40 agarase system was found to be comprised of three enzyme activities which synergistically combine to degrade the red algal polysaccharide, agar. {dollar}beta{dollar}-agarase I degrades the polymer to tetrasaccharide, {dollar}beta{dollar}-agarase II degrades tetramer to disaccharide and {dollar}alpha{dollar}-neoagarobiose hydrolase cleaves the dimer to the monosaccharides D-galactose and 3,6-anhydro-L-galactose.; Protein purification by HPLC and ammonium sulfate precipitation revealed that 2-40 contains two {dollar}beta{dollar}-agarase I enzymes. One degrades agarose to tetrasaccharide and disaccharide (approximately 98,000MW) and the other degrades agarose to tetrasaccharide only (approximately 42,000MW).; Regulatory studies, facilitated by zymogram techniques developed during this work, reveal that the agarase system is induced by agarose and its degradation intermediates; and it is repressed by D-glucose. The glucose effect is not allosteric and is relieved by the addition of exogenous cAMP in combination with agarose. The entire agarase system is coordinately regulated by selected carbon sources suggesting it may be organized in an operon.; 2-40 agarases as well as alginase, carrageenanase, and pullulanase are released from the cell during stationary phase. Electron microscopy studies revealed evidence of partial cell lysis in stationary phase growth, corresponding to the time of enzyme release. Cells may experience severe carbon limitation at this time in batch growth and release of degradative enzymes by such a mechanism could represent an act of altruism. The bulk of the population may die releasing enzymes which benefit the viable members of the community. |
