Decomposition of Marsh Grass by Aerobic Marine Bacteria

1. Aerobic, heterotrophic, marine bacteria have been found to participate actively in the decomposition of Spartina, both in the field and in the laboratory. Thirty-five per cent of 125 isolates obtained from sea water and marsh mud near Sapelo Island, Georgia, grew in sea water marsh grass extract medium more luxuriantly than in sea water Difco nutrient broth. 2. Assuming similar relationships to hold in nature and in the laboratory quantititive data provided an estimate that about eleven per cent of the annual crop of marsh grass may be rapidly converted to bacteria (dry weight basis). Microbial utilization of crude fiber takes place more slowly than decomposition and use of protein and soluble carbohydrate constituents. 3. Marsh mud extracts failed to serve as an enrichment medium for aerobic heterotrophic bacteria unless supplemented with organic materials, such as casein hydrolysate or grass extract. Supplements of dextrose, phosphate, or ammonium nitrate were generally ineffective. Numerous bacterial isolates from water and mud were able to grow well on extracts of Spartina in either natural or artificial sea water. 4. Bacterial isolates did not possess specific requirements for single amino acids, although growth in the presence of sources of amino nitrogen was generally better than on ammonium sulfate. Growth in the presence of multiple mixtures of pure amino acids or hydrolysed casein was better than growth on single amino acids. Among the combinations of pure amino acids studied, a mixture of alanine, aspartic acid, and glutamic acid yielded very good growth. 5. In the estuarine waters of the Georgia sea island region, where salinity varies greatly with changes in the seasons and tides, both euryhaline and stenohaline types of bacteria occur as natural adaptations to the fluctuating conditions of the environment.