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Bacterial and biophysical aspects of macroaggregation phenomena in the northern Adriatic Sea

Transformation of DOC pool into gelatinous clouds and surface layers (Stachowitsch et al. 1990) composed of polysaccharide matrix, microorganisms (Revelante, Gillmartin, 1991 ; Herndl, 1992) is a dramatic manifestation of microbially mediated POM-DOM transformation. Formation and transient stability of gelatinous macroaggregates (cm to km size) involves microscale bacterial processing of the organic matter (Azam, 1996, 1997). Here we also propose simultaneous involvement of a large scale phase transition from dispersed to a gel state. We studied sticking and hydrophobic-hydrophilic properties of fresh macroaggregate samples, collected at a Northern Adriatic transect during summer 1991 and 1997, using model hydrophobic interfaces. Relaxation electrochemical and spectroscopic techniques were used together with standard microscopy. Hydrophobic domains within the overall hydrophilic structure and microzones of lower oxygen content were identified in the fresh macroaggregate samples. In the majority of subsurface aggregate samples the rate of oxygen consumption was comparable to that of dense bacterial suspensions (Svetlicic et al, 1997). Differential Raman Spectra revealed OH streching of structured water in the gel. We propose that structural differences between the gel and the dispersed state should be accompanied by alternation in microbiological properties.

bacterial aspects; biophysical aspects; macroaggregation phenomena; Northern Adriatic

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