Microbiological Studies on the Decomposition of Chitin in Marine Environment-I

Abstract

The occurrence of chitinoclastic bacteria growing on plankton, suspended matter and in sea water at Aburatsubo Inlet was investigated for over a period of nearly one year. The results obtained are summarized as follows: 1. Marine chitinoclastic bacteria is widely distributed in sea water, on plankton and on suspended matter. The chitinoclastic bacteria constitutes less than 0.4 % of the total bacterial number in the neritic region. 2. The percentage of the chitinoclastic bacteria in the bacterial flora of suspended matter was higher than that obtained for plankton. A considerable number of chitinoclastic bacteria are, however, already attached on living copepods, and a correlation between the percentage of chitinoclasts in the bacterial flora of plankton and the percentage of planktonic crustaceans in plankton was observed. 3. The bacterial population in sea water, on plankton and on suspended matter increased slightly in summer and autumn, though their abundance was nearly equal all through the year. The percentage of chitinoclastic bacteria in each substratum showed an inverse relation with the COD of sea water. 4. All the isolated chitinoclastic bacteria were classified into the types of 5 species. Type LI appeared in Aburatsubo Inlet predominantly in summer, and Type HY appeared in winter and early spring, whereas Type IN and Type CH were always found on plankton and on suspended matter all through the year though they appeared dominantly in late spring and autumn while the interchange of Type LI and Type HY occurred in summer and winter and early spring respectively. 5. From experiments on the decomposition of Artemia in sea, it was found that the decomposition and liberation of easily destructible organic matter from plankton occurred within 4 days and the indestructible organic matter from plankton as chitin was later destroyed slowly. The increase of the bacterial population was rapid on dead Artemia and reached the stationary phase on the 4 th day, whereas chitinoclastic bacteria increased rapidly 2 days after Artemia died.