MARINE BACTERIA AND THEIR RÔLE IN THE CYCLE OF LIFE IN THE SEA

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Abstract
1. A study has been made of the proximate chemical composition of zoöplankton and of certain marine algæ, of their decomposition by marine bacteria, and of some of the bacteria capable of attacking certain carbohydrate constituents of marine plant life. 2. The zoöplankton was readily decomposed by bacteria in sea water and in marine mud media, with the result that more than a half of the total nitrogen present in the plankton was liberated as ammonia. Although the ammonia produced in the water and in the mud cultures was practically the same, a much greater amount of CO2 was liberated as a result of the decomposition of the plankton in the mud than in the water medium. 3. It is suggested that the protein constituents of the zoöplankton decompose alike in the water and in the mud cultures; however, other chemical constituents of the plankton, free from nitrogen, such as certain fats, or low in nitrogen, such as the chitins, seem to undergo more rapid decomposition in the mud than in the water. 4. In the decomposition of algal material by marine bacteria, the chemical composition of the algæ is of prime importance. In the case of Ulva lactuca, a green alga containing about 2 per cent nitrogen on a dry, salt-free basis, active decomposition took place both in the sea water and in the marine mud cultures. In the case of the brown alga Fucus vesiculosus, however, containing less than 1 per cent total nitrogen, very little decomposition took place in the sea water medium, but the material decomposed very actively in the mud medium. 5. The addition of inorganic sources of nitrogen to the Fucus material in the sea water cultures resulted in a much more active decomposition, due to the fact that this nitrogen was required by the bacteria decomposing the Fucus constituents for the synthesis of their cell substance. The presence of Fucus material in sea water may, therefore, result in a minimum amount of available nitrogen. A definite parallelism was found between the development of the bacteria in the culture and the amount of decomposition of the Fucus material, as measured by CO2 evolution. 6. Nitrate and ammonium salt were used readily as sources of nitrogen in the decomposition of the Fucus material by bacteria. The addition of an excess of nitrate to the culture proved to be injurious. This excess nitrate was rapidly destroyed by denitrifying bacteria. 7. The sea is found to harbor an extensive population of bacteria capable of utilizing cellulose and hemicelluloses. These bacteria represent a number of distinct types, varying considerably in their morphological and physiological properties. Some of the bacteria were found capable of attacking both cellulose and agar, while others decomposed either cellulose alone or agar alone. Some of these bacteria are also able to decompose a number of other polysaccharides, as well as various mono- and disaccharides.