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Legionella pneumophila is known as the causative agent of Legionnaires' disease and free-living amoebae (FLA) can serve as vehicles for legionellae. The aim of this study was to screen industrial waters for the occurrence of FLA and their co-occurrence with legionellae. A total of 201 water samples, including 129 cooling waters and 72 process waters, and 30 cooling lubricants were included in the study. Treated waters were screened periodically, pre and post treatment. Altogether, 72.6% of the water samples were positive for FLA, acanthamoebae being most prevalent (in 23.9% of the samples) followed by Vermamoeba vermiformis (19.4%). Only one cooling lubricant was positive (Acanthamoeba genotype T4). Legionella spp. were detected in 34.8% of the water samples and in 15% in high concentrations (>1000 CFU/100 ml). Altogether, 81.4% of the Legionella-positive samples were positive for FLA by standard methods. By applying a highly sensitive nested PCR to a representative set of random samples it was revealed that Legionella spp. always co-occurred with Acanthamoeba spp. Although the addition of disinfectants did influence amoebal density and diversity, treated waters showed no difference concerning FLA in the interphases of disinfection. It appears that FLA can re-colonize treated waters within a short period of time.

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RESUMEN

Floating riverine aggregates are composed of a complex mixture of inorganic and organic components from their respective aquatic habitats. Their architecture and integrity are supplemented by the presence of extracellular polymeric substances of microbial origin. They are also a habitat for virus-like particles, bacteria, archaea, fungi, algae, and protozoa. In this study we present different confocal laser scanning microscopy strategies to examine aggregates collected from the Danube and Elbe Rivers. In order to collect multiple types of information, various approaches were necessary. Small aggregates were examined directly. To analyze large and dense aggregates, limitations of the technique were overcome by cryo-sectioning and poststaining of the samples. The staining procedure included positive staining (specific glycoconjugates and cellular nucleic acid signals) as well as negative staining (aggregate volume) and multichannel recording. Data sets of cellular nucleic acid signals (CNAS) and the structure of aggregates were visualized and quantified using digital image analysis. The Danube and Elbe Rivers differed in their aggregate composition and in the relative contribution of specific glycoconjugate and CNAS volume to the aggregate volume; these contributions also changed over time. We report different spatial patterns of CNAS inside riverine aggregates, depending on aggregate size and season. The spatial structure of CNAS inside riverine aggregates was more complex in the Elbe River than in the Danube River. Based on our samples, we discuss the strengths and challenges involved in scanning and quantifying riverine aggregates.

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RESUMEN

In riverine water, both suspended particulate material and viruses are prominent ecological factors. The existence of various particle types and differences in viral abundance impose variability in microenvironments. Particulates and their microbial surrounding may interact in several ways, this interaction being strongly dependent on particle quality and the abundance of organisms involved. In laboratory experiments, we used different suspended matter types (fresh and aged mineral sediment and leaf litter, river snow) that typically occur in riverine environments as model particles. We investigated the effects of particle quality and different ambient viral abundances (×1, ×2 enrichments, and inactivated viruses) on several microbial parameters (changes in bacterial and viral abundances, bacterial production, specific bacterial production) of both the free-living and particle-attached fractions using water from a floodplain system of the Danube River (Austria). Both seston quality and variable viral abundances in the bulk water influenced some microbial parameters. The average abundance of bacteria and viruses was significantly higher on organic than on inorganic particles and on aged particles (for both sediment and leaf litter). Changes in bacterial abundance during the course of the experiments were also influenced by particle quality, with, for example, aged sediment favoring increasing abundances. Virus:bacterium ratios (VBR) were significantly higher on organic than on inorganic particles, but significantly lower on suspended particles than in the plank-tonic fraction. Typically, bacterial secondary production (overall and cell-specific) was higher on particles than in bulk water. Bacterial productivity in the ambient water was negatively affected by the abundance of planktonic viruses but positively affected by that of attached viruses. These findings from experimental systems may foster in situ studies of particle-rich environments.