Jose Vives-Rego

Some kinetic characteristics of exoproteolytic activity in coastal seawater

Abstract The response of the exoproteolytic activity of seawater to proteolytic inhibitors suggests that metalloproteases are the main enzymes involved. The K m of exoproteolytic enzymes for the hydrolysis of indigenous proteins in coastal north seawater has been evaluated as 80 μg l −1 and the maximum rate of proteolysis lies in the range 0·1–0·35 μgC l −1 -enzymatic-unit −1 . Enrichment experiments suggest that both species selection and metabolic regulation may play a role in the exoproteolytic activity/biomass ratio. However, in situ exoproteolytic activity/biomass ratios observed in a broad range of natural marine environments lie in a very narrow range, which is intermediate between those observed after amino acid or protein enrichment.

Survival ofLegionella pneumophila in the aquatic environment.

Survival ofLegionella pneumophila SG 1 in seawater and river water was assessed using plate counts on buffered charcoal yeast extract agar amended with α-ketoglutarate (BCYEα) and [3H]thymidine-labeling. The [3H]thymidine-labeling method for assessing survival ofL. pneumophila in aquatic environments was compared with viable counts, direct fluorescent microscopy (DFA), and acridine orange direct counts (AODC). Protozoa were isolated from the samples employed in the study and identified by characteristic trophozite and cyst morphology. Selective filtration employing 2.0 μm Nucleopore filters was used to determine the effect of grazing on survival ofL. pneumophila in seawater and river water.Legionella viability as measured by plate counts (CFU/ml), declined to a greater extent than cell lysis, assessed by thymidine, DFA, and AODC counts, suggesting thatL. pneumophila survives in aquatic habitats to a greater extent than revealed through culturable counts.

Estimation of "Escherichia coli" mortality in seawater by the decrease in 3H-label and electron transport system activity

The mortality ofEscherichia coli in seawater was assessed by viable counts, electron transport system activity, and cellular3H-labelling. Filtration was used to assess the grazing mortality. Cellular radiolabelling and electron transport system activity were useful methods for assessingE. coli survival in seawater. The decrease in the3H-label as a method to assess bacterial mortality was validated by using viable counts and metabolic activity assays. The particulate fraction that passed 2 μm but was retained on 0.2 μm pore-size filters was the primary reason forE. coli mortality in seawater.

Assessment of bacterial production and mortality in Mediterranean coastal water

Abstract Bacterial production was estimated by thymidine incorporation using conversion factors estimated from the increase in bacterial abundance and thymidine incorporation in batch incubations. Grazing and bacterial mortality were estimated from the disappearance of the 3 H-label of natural assemblages in filtered and unfiltered samples. The approach was also used to calculate bacterial production (about 0·2 × 10 9 cells l −1 h −1 ). Bacterial mortality was about 0·02 h −1 and grazing represented 15–82% of the total mortality in a Mediterranean coastal water.

Mortality of marine bacterial strains in seawater

As an approach for assessing the dynamics of bacterial population in seawater, the survival of five isolated marine bacteria strains was assessed by the disappearance of radioactivity in the cold trichloroacetic acid (TCA)-insoluble fraction from a previously3H-labeled culture. Metabolic activity during survival experiments was assessed by the measurement of electron transport system (ETS) activity. Fractionated filtration was used to assess the grazing mortality. The particulate fraction that passed 2.0 μm and was retained in 0.2 μm was the main cause of mortality.