Luis Egea

Bacterial Colonization and Ectoenzymatic Activity in Phytoplankton-Derived Model Particles: Cleavage of Peptides and Uptake of Amino Acids

A bstractPhytoplankton-derived model particles were created in laboratory from a mixture of autoclaved diatom cultures. These particles were colonized by a marine bacterial community and incubated in rolling tanks in order to examine the relationship between aminopeptidase activity and leucine uptake. Bacteria inhabiting particles and ambient water were characterized for abundance, biovolume, aminopeptidase activity, leucine uptake, and growth rate. Particles were a less favorable habitat than ambient water for bacterial growth since growth rates of particle-attached bacteria were similar or even lower than those of free-living bacteria. During the first ∼100 h of the particle decomposition process, there were not statistically significant differences in the aminopeptidase activity:leucine uptake ratio between attached and free-living bacteria. From ∼100 h to ∼200 h, this ratio was higher for attached bacteria than for free-living bacteria. This indicates an uncoupling of aminopeptidase activity and leucine uptake. During this period, attached and free-living bacteria showed similar hydrolytic activities on a cell-specific basis. In the free-living bacterial community, variations in aminopeptidase activity per cell were associated with variations in leucine uptake per cell and growth rates. However, in the attached bacterial community, when leucine uptake and growth rates decreased, aminopeptidase activity remained constant. Thus, after ∼100 h, particle-attached bacteria were not taking advantage of their high aminopeptidase activity; consequently the hydrolysed amino acids were released into the ambient water, supporting the growth of free-living bacteria. These results demonstrate that over the particle decomposition process, the relationship between hydrolysis and uptake of the protein fraction shows different patterns of variation for attached and free-living bacterial communities. However, in our experiments, this uncoupling was not based on a hyperproduction of enzymes by attached bacteria, but on lower uptake rates when compared to the free-living bacteria.

Direct viable count of Gram-positive and Gram-negative bacteria using ciprofloxacin as inhibitor of cellular division

Abstract Following the method described by Kogure et al. (Can. J. Microbiol. 25 (1979) 415–420), we used ciprofloxacin, a quinolone which inhibits cell division of Gram-positive and Gram-negative bacteria, to quantify the number of viable bacteria in a series of cultures. As test bacteria we used three Escherichia coli strains, two of them sensitive to nalidixic acid and a third resistant to this inhibitor, and three Gram-positive bacteria: one rod ( Lactobacillus plantarum ) and two cocci ( Enterococcus faecalis and Micrococcus varians ). Ciprofloxacin is an efficient inhibitor of cell division in all six strains, although the effect on the morphology of the rods and cocci was clearly different. The percentage of viable bacteria was determined in the case of the rods by the increase in either length or biovolume and, for the cocci, by the increase in cell biovolume. Image analysis was required to detect variations in cell biovolume in the case of cocci and rods. For nalidixic acid-sensitive strains, it was possible to use both, as similar percentages of viable bacteria were detected with both inhibitors. The differences between the colony forming units (CFU) and direct viable (DVC) counts were much higher in the strains showing typical arrangements than in those strains without them. Finally, we found no significant differences in the number of viable bacteria in the natural population of the Butron river when we used either ciprofloxacin or nalidixic acid as inhibitors of cell division.

Factors affecting the survival of E. coli in a river

The relationships between physical, chemical and microbial characteristics of an aquatic ecosystem and the survival of E. coli have been studied. Two conditions of the ecosystem (warm and cold) are considered. T90 (time necessary for 90% of a bacterial population to die) in the warm situation shows an inverse exponential relationship with water temperature. Besides the direct relationship temperature-T90, there is an indirect effect of temperature upon T90 through the natural microflora of the water. The relationships between temperature and the heterotrophic population, and between the heterotrophic population and the bacterial consumers (P.F.U.), are exponential and linear, respectively.

Influence of light and natural microbiota of the Butrón river on E. coli survival

The survival of an E. coli strain in water samples from the Butrón river has been studied. The input of E. coli cells in the aquatic system breaks down the established balance among the components of the natural microbiota: E. coli becomes the object of the active protozoal predation whereas the autochtonous heterotrophic community become alternative preys. As a result of this new situation, the natural microbiota increases but returns to the initial values once the E. coli cells have been removed from the system. The effect of the temperature of incubation on the survival is exerted through the effect of this parameter on the predatory activity of the protozoa. Light has a lethal and direct action on the E. coli cells, the effect of this parameter is even superior to that of predation.

Channeling of bacterioplanktonic production toward phagotrophic flagellates and ciliates under different seasonal conditions in a river

The objective of this study was to analyze the flux of biomass through the communities of bacteria and phagotrophic protists in the cold and warm conditions occurring seasonally in Butrón River. Bacterial and heterotrophic protistan (flagellate and ciliate) abundance was determined by epifluorescence direct counts; protistan grazing on planktonic bacteria was measured from fluorescently labeled bacteria uptake rates; and the estimate of bacterial secondary production was obtained from [3H]thymidine incorporation rates. The abundance of bacterial, flagellate, and ciliate communities was similar during cold and warm situations. However, we observed that estimates of dynamic parameters, i.e., secondary bacterial production and protistan grazing, in both situations were noticeably different. In the warm situation, grazing rates of flagellates and ciliates (bacteria per protist per hour) were, respectively, 7 times and 18 times higher than those determined in the cold situation, and the grazing rates of the protistan communities (bacteria per protists present in 1 ml of water per hour) increased up to 5 times in the case of flagellates and 42 times in the case of ciliates. Estimates of bacterial secondary production were also higher during the warm situation, showing a ninefold increase. The percentage of bacterial production preyed upon by flagellates or ciliates was not significantly different between the two conditions. These results showed that in the different conditions of a system, the flux of biomass between the trophic levels may be quite different although this process may not be reflected in the abundance of each community of bacteria, flagellates, and ciliates.

Enumeration, Isolation and Some Physiological Properties of Actinomycetes from Sea Water and Sediment

Summary Nine selective culture media were used for counting actinomycetes in marine water and sediments. The presence of glycerol and/or asparagine in the media favoured the growth of these microorganims. Thermic treatment of sediment samples resulted in a selective reduction of the non-actinomycetal heterotrophic microflora. However, the same treatment of water samples had a negative effect on the actinomycetal flora. Actinomycetes in water and sediment represented 3–4% and 5–6% of the total flora, respectively. 72.7% of the isolated strains were Streptomyces, 20.5% Micromonospora and 7% Nocardia. The isolated actynomycetes strains, especially Streptomyces, showed a high hydrolytic activity for macromolecules and non-viable Gram-negative cells. Antimicrobial activity increased when sea water was present in the culture medium.

Attached and free-liviing dividing bacteria in two aquatic systems

The percentage of dividing biomass was calculated for attached and free‐living bacteria, in a coastal marine and a freshwater system. In the marine system with low concentrations of total and dissolved organic carbon (TOC and DOC) the percentage of dividing biomass was higher for attached (41.4 ± 13.9) than for the free‐living bacteria (22.0 ± 11.7). However, in the freshwater system, which had a higher concentration of TOC and DOC, the percentage of dividing biomass was similar for both communities‐attached (53.4 ± 26.5) and free‐living (78.4 ± 21.9). Thus the attachment to particulate material is not necessarily an advantage in waters where dissolved organic nutrients are readily available.