Ryszard J. Chróst

Microbial ecology of Lake Plußsee

Lake Plusssee is a small eutrophic kettle lake in northern Germany. Because it is sheltered and has no inflow from rivers, the Plusssee exhibits stable stratification and is especially suitable for limnological studies. This book presents the results of extensive research conducted on the ecophysiology of micro-organisms - principally bacteria - at the Plusssee over the past several decades. It begins with three chapters on the general limnological state of the lake: physical factors, inorganic nutrients, plankton composition and succession, fish fauna, etc. These chapters are followed by discussions of dissolved organic matter and photosynthetic production of organic matter by phytoplankton. The remainder of the book addresses the dynamics of structure, function and metabolism of the micro-organisms in the Plusssee.

Factors controlling bacteria and protists in selected Mazurian eutrophic lakes (North-Eastern Poland) during spring

BackgroundThe bottom-up (food resources) and top-down (grazing pressure) controls, with other environmental parameters (water temperature, pH) are the main factors regulating the abundance and structure of microbial communities in aquatic ecosystems. It is still not definitively decided which of the two control mechanisms is more important. The significance of bottom-up versus top-down controls may alter with lake productivity and season. In oligo- and/or mesotrophic environments, the bottom-up control is mostly important in regulating bacterial abundances, while in eutrophic systems, the top-down control may be more significant.ResultsThe abundance of bacteria, heterotrophic (HNF) and autotrophic (ANF) nanoflagellates and ciliates, as well as bacterial production (BP) and metabolically active cells of bacteria (CTC, NuCC, EST) were studied in eutrophic lakes (Mazurian Lake District, Poland) during spring. The studied lakes were characterized by high nanoflagellate (mean 17.36 ± 8.57 × 103 cells ml-1) and ciliate abundances (mean 59.9 ± 22.4 ind. ml-1) that were higher in the euphotic zone than in the bottom waters, with relatively low bacterial densities (4.76 ± 2.08 × 106 cells ml-1) that were lower in the euphotic zone compared to the profundal zone. Oligotrichida (Rimostrombidium spp.), Prostomatida (Urotricha spp.) and Scuticociliatida (Histiobalantium bodamicum) dominated in the euphotic zone, whereas oligotrichs Tintinnidium sp. and prostomatids Urotricha spp. were most numerous in the bottom waters. Among the staining methods used to examine bacterial cellular metabolic activity, the lowest percentage of active cells was recorded with the CTC (1.5–15.4%) and EST (2.7–14.2%) assay in contrast to the NuCC (28.8–97.3%) method.ConclusionsIn the euphotic zone, the bottom-up factors (TP and DOC concentrations) played a more important role than top-down control (grazing by protists) in regulating bacterial numbers and activity. None of the single analyzed factors controlled bacterial abundance in the bottom waters. The results of this study suggest that both control mechanisms, bottom-up and top-down, simultaneously regulated bacterial community and their activity in the profundal zone of the studied lakes during spring. In both lake water layers, food availability (algae, nanoflagellates) was probably the major factor determining ciliate abundance and their composition. In the bottom waters, both groups of protists appeared to be also influenced by oxygen, temperature, and total phosphorus.

Molecular (PCR-DGGE) versus morphological approach: analysis of taxonomic composition of potentially toxic cyanobacteria in freshwater lakes.

BackgroundThe microscopic Utermöhl method is commonly used for the recognition of the presence and taxonomic composition of potentially toxic cyanobacteria and is especially useful for monitoring reservoirs used as drinking water, recreation and fishery resources. However, this method is time-consuming and does not allow potentially toxic and nontoxic cyanobacterial strains to be distinguished. We have developed a method based on denaturing gradient gel electrophoresis (DGGE) of the marker gene ITS and the mcy-gene cluster, and DNA sequencing. We have attempted to calibrate the DGGE-method with a microscopic procedure, using water samples taken in 2011 from four lakes of the Great Mazurian Lakes system.ResultsResults showed that the classic microscopic method was much more precise and allowed the classification of the majority of cyanobacterial taxa to the species or genus. Using the molecular approach, most of the sequences could only be assigned to a genus or family. The results of DGGE and microscopic analyses overlapped in the detection of the filamentous cyanobacteria. For coccoid cyanobacteria, we only found two taxa using the molecular method, which represented 17% of the total taxa identified using microscopic observations. The DGGE method allowed the identification of two genera of cyanobacteria (Planktothrix and Microcystis) in the studied samples, which have the potential ability to produce toxins from the microcystins group.ConclusionsThe results confirmed that the molecular approach is useful for the rapid detection and taxonomic distinction of potentially toxic cyanobacteria in lake-water samples, also in very diverse cyanobacterial communities. Such rapid detection is unattainable by other methods. However, with still limited nucleotide sequences deposited in the public databases, this method is currently not sufficient to evaluate the entire taxonomic composition of cyanobacteria in lakes.

The Role of Planktonic Organisms in Urea Metabolism in Lakes of Temperate Zone - Case Study

ABSTRACT Although urea is the simplest N-containing organic compound ubiquitous in all aquatic environments, its role in N-nutrition of planktonic biota and relevance for eutrophication of freshwater ecosystems is still insufficiently defined and often bypassed. The dynamics of production of autochthonous urea as well as maximal potential net ureolytic activity (net URA Vmax) of phyto- and bacterioplakton were studied in mesocosm experiment and verified during the field studies conducted in the Great Mazurian Lake system (GMLS). Analysis of the obtained results revealed that the proteins were the main autochthonous urea precursors. Urea concentration in the studied mesocosms and in GMLS surface waters was positively correlated with flagellate, ciliate and crustacean biomass and, less evidently, with bacterial biomass (BB). In surface waters of GMLS net URA Vmax, similarly as urea concentrations, increased with their trophic status. Analysis of correlation of potential ureolytic activity with chlorophylla, (Chla) BB and L-leucine aminopeptidase activity (AMP) in lakes of different trophic status suggests that although both groups of planktonic microorganisms participated in urea decomposition processes, in eutrophic ones bacterial decomposition of urea is more evident. In highly eutrophic lakes excess of phosphorus induced higher nitrogen requirement resulting in the increase in protein decomposition rate. Intensified protein degradation resulted faster urea production, which finally induced higher ureolytic activity of planktonic microorganisms. In profundal waters of GMLS potential ureolytic activity was distinctly lower than in surface waters. This was caused by low temperature of hypolymnetic waters, inhibitory effect of hydrogen sulphide and lack of phytoplankton, which is known as a primary urea consumer.

Introduction: Aims, Problems, and Solutions in Aquatic Microbial Ecology

The ultimate aim of ecology is to understand the relationships of all organisms to their environment. Thus, in very general terms, the duty of the ecologist is to examine a particular environment, estimate the abundance of individuals of each species that make up the populations, recognize the communities, and determine their activities and their interactions with both related species and the rest of the community. Stated this way, the problems of the microbial ecologist are obvious and difficult. Semantic problems often arise when a group of botanists, zoologists, and microbiologists try to discuss general ecological theory. Macroecological studies always start by defining the species composition and then proceed to draw certain conclusions on the role of these species in the ecosystem. However, the taxonomic name of the individual isolate of an aquatic bacterium (if any name can be given to it) in only a few instances gives us any indication of its role in the ecosystem. The uncertain state of microbial and especially bacterial classical taxonomy (based on isolation techniques and determination of morphology and in vitro biochemical characteristics of isolates) makes determination of each species of aquatic bacteria almost impossible, except in a few, well-defined instances. As a result, the microbial ecologist has had to rely on methods that have attempted to measure the biomass or activity of a very large conglomerate of coexisting microbial taxa in the aquatic environment. For a long time this has caused the very slow development of microbial ecology concepts and application of a general ecological theory to the microbial ecology.

Quantitative description of respiration processes in meso-eutrophic and eutrophic freshwater environments

We propose a modification of measurement methodology allowing the overall respiration rate (VResp) close to the in situ conditions; size of the labile, respirable organic matter pool (OMResp); and its turnover time (Tt) to be calculated. In addition to the respiration of dissolved substrates by free-living bacteria, the respiration of attached bacteria and other planktonic organisms is also taken into account. In case study we evaluated the modified, quantitative description of respiration processes in surface waters of lakes of different trophic status: mezzo-eutrophic and eutrophic. In both types of studied environments, VResp oscillated between 1.0 μmol C l-1 h-1 and 3.0 μmol C l-1 h-1, and the size of the OMResp pool varied from 39.3 μM C to 828.7 μM C. Despite of higher OMResp concentrations in eutrophic lakes, we found a lower susceptibility of OM to respiration processes in eutrophic than in meso-eutrophic lakes but similar VResp in both types of lakes. We conclude that the proposed method allows a fast quantitative description of labile organic matter utilization by aerobic aquatic microorganisms.

Coomassie Blue G250 for Visualization of Active Bacteria from Lake Environment and Culture

Bacteria play a fundamental role in the cycling of nutrients in aquatic environments. A precise distinction between active and inactive bacteria is crucial for the description of this process. We have evaluated the usefulness of Coomassie Blue G250 for fluorescent staining of protein containing potentially highly active bacteria. We found that the G250 solution has excitation and emission properties appropriate for direct epifluorescence microscopy observations. It enables fast and effective fluorescent visualization of living, protein-rich bacteria, both in freshwater environment and culture. Our results revealed that the number of G250-stained bacteria from eutrophic lake was positively correlated with other standard bacterial activity markers, like number of bacteria containing 16S rRNA, bacterial secondary production or maximal potential leucine-aminopeptidase activity. In case of the E. coli culture, the percentage of bacteria visualized with G250 was similar to that of bacteria which accumulated tetracycline. Compared to other common methods utilizing fluorogenic substances for bacteria staining, the approach we evaluated is inexpensive and less hazardous (for example mutagenic) to the environment and researchers. It can be regarded as an additional or alternative method for protein rich, active bacteria staining.

The Relationship between Primary Production and Respiration in the Photic Zone of the Great Mazurian Lakes (GMLS), in Relation to Trophic Conditions, Plankton Composition and Other Ecological Factors

ABSTRACT The relation of primary production to respiration and dependence of both processes on various environmental factors were investigated in the surface waters of lakes of The Great Mazurian Lake System (GMLS) during summer seasons 2009–2011. Primary production and extracellular release was determined by 14C method, respiration (dark oxygen consumption) - by Winklers method. Collected results allow to conclude that: (i) in all studied lakes primary production was primarily cyanobacterial, although in mesotrophic ones participation of eukaryotic phytoplankton in light CO2 fixation was more pronounced; (ii) in mesotrophic part of GMLS primary production was limited alternately by N and P availability and less dependent on N and P regeneration processes, whereas in southern, eutrophic lakes it was primarily fueled by regeneration of biogenic substances from organic compounds and strongly limited by N resources; (iii) although in photic zone of whole GMLS respiration was dominated by heterotrophic bacteria, in its mesotrophic part also participation of other plankton components in respiration processes was significant and, (iv) that in eutrophic lakes planktonic respiration was more dependent on low molecular weight products liberated enzymatically from organic substrates than on organic compounds released by primary producers. The mean production to respiration ratio, which varied from 2.11 to 2.60 in northern, and from 2.05 to 3.67 in southern lakes suggested that during period of investigations photic zones of lakes of both parts of GMLS were net autotrophic systems.

Bacterial Life in the Plußsee: General Remarks on Aquatic Microbial Ecology

Until recently it was thought that heterotrophic bacteria in aquatic ecosystems played only a trivial role in organic fluxes and in the functioning of the ecosystem. It was commonly accepted that phytoplankton primary production was utilized predominantly by herbivores (mainly zooplankton) and passed on to the organisms that comprise the grazing food chain. Even in recently published, widely distributed books on limnology, bacteria are still treated as only remineralizers and/or decomposers of organic matter in the energy and organic matter fluxes throughout a lake ecosystem (Wetzel 1983, Cole 1988, Schwoerbel 1987, Sommer 1989, Lampert and Sommer 1993). Very little attention has been directed to further implications of bacterial dynamics for the trophic relationships between these microorganisms and higher trophic levels and the functioning of the lake ecosystem. This notion has changed significantly during the last decade with results from new methods of measuring bacterial production, biomass and activity of bacteria, and their in situ growth rates. In an ecosystem context, these new findings portray bacteria as a very dynamic metabolic and trophic component representing a major pathway for organic matter and energy flux in the aquatic food web (Sherr and Sherr 1988, Ducklow and Carlson 1992, Simon et al. 1992, Chrost 1992).