CELL-BOUND AND EXTRACELLULAR LAMINARINASE ACTIVITY IN DENDRYPHIELLA-SALINA AND 5 OTHER MARINE FUNGI

Six species of marine fungi were able to use laminarin as a carbon source. The rates of disappearance of carbohydrate were similar to those obtained when the fungi were grown on glucose. Laminarinase activity (E. C. 3.2.1.58) was associated mainly with the fungal mycelia: in four of the fungi only 5 - 20% of the total activity was detected in the culture fluids, while in the remaining two species both mycelial and extracellular activities were very low. Quantitative growth studies of one fungus, Dendryphiella salina, showed that the mycelial activity was proportional to dry weight (determined by chitin measurements) over the growth phase of the fungus and confirmed the low levels of extracellular activity. The ratio of cell-bound to extracellular enzyme activity was little altered by changes in growth conditions, viz. agitation, medium composition, buffering and salinity. The mycelial enzyme from D. salina had a pH optimum of 4.6 and produced only glucose when incubated with laminarin. The appearance of free glucose during growth on laminarin by D. salina and the other five fungi examined indicated that the levels of laminarinase in these organisms did not limit their growth on the polysaccharide. These results show that marine fungi are capable of degrading laminarin, and may therefore have a role in the breakdown of seaweed.