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LAP ACTIVITY IN AQUATIC ECOSYSTEMS 959

tent in¯uence on LAP levels; the signi®cant positive corre- Approaches ed. Overbeck, J. and Chrost, R.J. pp. 47±78. New
lations found between this enzyme and chlorophyll and York: Springer-Verlag.
POC contents suggest that the greater organic loading, Hoppe, H.G. (1983) Signi®cance of exoenzymatic activities in the
being an available source of carbon for bacterial metabo- ecology of brackish water: measurements by means of methy-
lism, further induces the enzyme production. Therefore, it lumbelliferyl-substrates. Marine Ecology Progress Series 11, 299±
may be hypothesized that, besides biological factors, all the 308.
hydrological and chemical features of the different ecosys- Hoppe, H.G. (1986) Relations between bacterial extracellular
tems may exercise a strong in¯uence on microbial activity. enzyme activities and heterotrophic substrate uptake in a brack-
A similar conclusion has also been suggested by Misic and ish water environment. Actes de Colloques, Gerbam-Ifremer 3,
Fabiano (1996), who reported a summary of the values of 119±128.
leucine aminopeptidase recorded by various authors in dif- Hoppe, H.G., Kim, S.J. and Gocke, K. (1988) Microbial decom-
position in aquatic environments: combined process of extracel-
ferent areas of the world.
lular enzyme activity and substrate uptake. Applied and
Although the LAP assay provides only potential infor-
Environmental Microbiology 54, 784±790.
mation on proteolytic activity, this determination in natural
Hoppe, H.G., Giesenhagen, H.C. and Gocke, K. (1998) Changing
ecosystems is of great ecological signi®cance, and contri-
patterns of bacterial substrate decomposition in a eutrophication
butes to knowledge of the microbial potentialities over the
gradient. Aquatic Microbial Ecology 15, 1±13.
organic matter pool and consequently to the estimation of
Karner, M., Fuks, D. and Herndl, G.J. (1992) Bacterial activity
the role played by bacteria in biogeochemical processes.
along a trophic gradient. Microbial Ecology 24, 243±247.
Leonardi, M., Azzaro, F., Bonaccorso, A. et al. (1998a) Dati preli-
ACKNOWLEDGEMENTS minari sulle caratteristiche idrobiologiche del sistema acqua-
sedimento nell'area delle Isole Egadi (Campagna oceanogra®ca
The authors are grateful to the other operating units of the EGA 96). Atti Associazione Italiana Oceanologia e Limnologia 12,
0
Prisma 1 and 2 Projects (Dr A. Puddu and M. Pettine, 377±386.
IRSA, Rome; Dr S. Rabitti, IBM, Venice; Dr Franco Leonardi, M., Caruso, G., Monticelli, L. and Zaccone, R. (1998b)
Decembrini, IST, Messina) and to Dr Marcella Leonardi Spatial and temporal variations of microbial processes on
and Luis Monticelli, IST, Messina, who kindly provided organic matter in Oliveri-Tindari coastal ponds (Sicily, Italy).
physical±chemical data supporting this study. In Proceedings of the VII International Congress of Ecology July
19±25, 1998, Firenze (Italy) ed. Farina, A., Kennedy, J. and
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= 2000 The Society for Applied Microbiology, Journal of Applied Microbiology, 89, 951ÿ959