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Archo Oceanogr. Limnol. 22 (2001), 199-206
Istituto di Biologia del Mare, Venezia, Italia

SPATIAL AND TEMPORAL VARIATIONS IN MICROBIAL ACTIVITY IN
THE MEDITERRANEAN SEA

R. ZACCONE, R. LA FERLA, M. AZZARO, G. CARUSO AND E. CRISAFI

Istituto Sperimentale Talassografico – CNR, Spianata S. Raineri, 86 – 98122 Messina

INTRODUCTION

The cycle of organic substances in the sea is strongly influenced by metabolic
processes carried out by microorganisms within the microbial loop. In particular,
heterotrophic bacteria are responsible for hydrolysis of a considerable fraction of the
photosynthetic production both in particulate form (POM) and dissolved form
(DOM) through their ectoenzymatic activity (EEA). The production of ectoenzymes
is closely correlated to the availability of polymeric substrates or the lack of directly
utilizable monomers. Hydrolysis products, transported to the inside of the cell, are in
part used for the production of bacterial biomass (BCP, Bacterial Carbon
Production). The coupling of hydrolysis and uptake processes increases the
utilization efficiency of DOM by aquatic bacteria (Chrost, 1993).

Thereafter, the produced biomass is oxidised during respiration, with the release
of CO2 and nutrients in the aquatic systems in a newly assimilable form by primary
producers. Furthermore, the respiration rates along the water column provide an
index of the export of phytoplanktonic photosynthetic products towards the oceanic
depths and as a consequence the oceans constitute a reservoir of CO2 in the deepest
layers.

Organic matter decomposition by means of ectoenzymatic activity and oxidation
by means of respiration are the processes by which the input and output of C
through the bacterial cells occur.

Microbial enzymatic and respiratory activities in the Mediterranean have been
studied in the last years. The Mediterranean basin is, from a biogeochemical point of
view, strongly conditioned by the morphology of the straits, which subdivide it into
different sub-basins with peculiar characteristics affecting the trophic levels in the
system. In this paper an overview of recent studies on the hydrolytic and respiratory
activities observed in areas with different trophic conditions is reported.