Biomedical subjects

Markus G Weinbauer

Publications and source records attributed to Markus G Weinbauer.

6 recordsLinked to original sources

PubMed2006

The response of Vibrio- and Rhodobacter-related populations of the NW Mediterranean Sea to additions of dissolved organic matter, phages, or dilution.

We investigated the growth response of the heterotrophic prokaryotic community focusing on Vibrio- and Rhodobacter-related populations (SRF3) to variation in the availability of dissolved organic matter (DOM), population density-dependent effects, and prokaryotic virus (phage) infection in coastal and offshore waters of the NW Mediterranean Sea. We tested the response of the prokaryotic community to three different DOM fractions prepared by ultrafiltration. One of the DOM fractions contained phages (<0.2 m), a second was virus-free (<100 kDa), and a third contained only low molecular weight (<1 kDa). The proportion of Vibrio and SRF3 populations as determined by fluorescent in situ hybridization in the community ranged from <1 to 6.2% and from 3.2 to 6.3%, respectively. Based on changes in cell numbers, growth rates ranged from 2.1 to 3.1 day(-1) for Vibrio and from 0.8 to 1.2 day(-1) for SRF3. Growth rates of Vibrio were similar or higher than those of the total prokaryotic community, whereas the ability of Vibrio to use high molecular weight (HMW) DOM and the responses to additions of phage-rich material were lower. Growth rates of SRF3 were lower than that of the community. Susceptibility to infection of SRF3 was sometimes lower than in the community, whereas the growth stimulation of HMW DOM was similar or lower. Reducing the cell concentrations of the prokaryotic community by dilution stimulated the overall growth of the community, including that of its constituent Vibrio and SRF3 populations, but the effect was smaller on the SRF3 and greater on Vibrio populations than for the total community. Comparisons with the community also revealed that life strategy traits of bacterial populations differed between coastal and offshore waters. Overall, our data suggest that Vibrio is an r-strategist or opportunistic population in the NW Mediterranean Sea, whereas SRF3 is a K-strategist or equilibrium population.

Bacteriophages↗

PubMed2005

Modelling viral impact on bacterioplankton in the North Sea using artificial neural networks.

The temporal variability of the viral impact on bacterioplankton during the summer-winter transition in the North Sea was determined and artificial neural networks (ANNs) were developed to predict viral production and the frequency of infected bacterial cells (FIC). Viral production and FIC were estimated using a virus-dilution approach during four cruises in the southern North Sea between July and December 2000 and an additional cruise in June 2001. Supplementary data such as bacterial production, and bacterial and viral abundance were collected to relate changes in FIC and viral production to the dynamics of other biotic parameters. Average viral abundance varied between 4.4 x 10(6) ml(-1) in December and 29.8 x 10(6) ml(-1) in July. Over the seasonal cycle, viral abundance correlated best with bacterial production. Average bacterial abundance varied between 0.5 x 10(6) ml(-1) in December and 1.3 x 10(6) ml(-1) in July. Monthly average values of FIC ranged from 9% in September to 39% in June and the average viral production from 11 x 10(4) ml(-1) h(-1) in December to 35 x 10(4) ml(-1) h(-1) in July. The data set was used to develop ANN-based models of viral production and FIC. Viral production was modelled best using sampling time, and bacterial and viral abundance as input parameters to an ANN with two hidden neurons. Modelling of FIC was performed using bacterial production as an additional input parameter for an ANN with three hidden neurons. The models can be used to simulate viral production and FIC based on regularly recorded and easily obtainable parameters such as bacterial production, bacterial and viral abundance.

Bacteria↗

PubMed2004

Ecology of prokaryotic viruses.

The finding that total viral abundance is higher than total prokaryotic abundance and that a significant fraction of the prokaryotic community is infected with phages in aquatic systems has stimulated research on the ecology of prokaryotic viruses and their role in ecosystems. This review treats the ecology of prokaryotic viruses ('phages') in marine, freshwater and soil systems from a 'virus point of view'. The abundance of viruses varies strongly in different environments and is related to bacterial abundance or activity suggesting that the majority of the viruses found in the environment are typically phages. Data on phage diversity are sparse but indicate that phages are extremely diverse in natural systems. Lytic phages are predators of prokaryotes, whereas lysogenic and chronic infections represent a parasitic interaction. Some forms of lysogeny might be described best as mutualism. The little existing ecological data on phage populations indicate a large variety of environmental niches and survival strategies. The host cell is the main resource for phages and the resource quality, i.e., the metabolic state of the host cell, is a critical factor in all steps of the phage life cycle. Virus-induced mortality of prokaryotes varies strongly on a temporal and spatial scale and shows that phages can be important predators of bacterioplankton. This mortality and the release of cell lysis products into the environment can strongly influence microbial food web processes and biogeochemical cycles. Phages can also affect host diversity, e.g., by 'killing the winner' and keeping in check competitively dominant species or populations. Moreover, they mediate gene transfer between prokaryotes, but this remains largely unknown in the environment. Genomics or proteomics are providing us now with powerful tools in phage ecology, but final testing will have to be performed in the environment.

Bacteria↗

PubMed2004

Are viruses driving microbial diversification and diversity?

Viruses can influence the genetic diversity of prokaryotes in various ways. They can affect the community composition of prokaryotes by 'killing the winner' and keeping in check competitive dominants. This may sustain species richness and the amount of information encoded in genomes. Viruses can also transfer (viral and host) genes between species. Such mechanisms have probably influenced the speciation of prokaryotes. Whole-genome sequencing has clearly revealed the importance of (virus-mediated) gene transfer. However, its significance for the ecological performance of aquatic microbial communities is only poorly studied, although the few available reports indicate a large potential. Here, we present data supporting the hypothesis that viral genes and viral activity generate genetic variability of prokaryotes and are a driving force for ecological functioning and evolutionary change.

Bacteria↗

PubMed2004

Impact of virioplankton on archaeal and bacterial community richness as assessed in seawater batch cultures.

During cruises in the tropical Atlantic Ocean (January to February 2000) and the southern North Sea (December 2000), experiments were conducted to monitor the impact of virioplankton on archaeal and bacterial community richness. Prokaryotic cells equivalent to 10 to 100% of the in situ abundance were inoculated into virus-free seawater, and viruses equivalent to 35 to 360% of the in situ abundance were added. Batch cultures with microwave-inactivated viruses and without viruses served as controls. The apparent richness of archaeal and bacterial communities was determined by terminal restriction fragment length polymorphism (T-RFLP) analysis of PCR-amplified 16S rRNA gene fragments. Although the estimated richness of the prokaryotic communities generally was greatly reduced within the first 24 h of incubation due to confinement, the effects of virus amendment were detected at the level of individual operational taxonomic units (OTUs) in the T-RFLP patterns of both groups, Archaea and Bacteria. One group of OTUs was detected in the control samples but was absent from the virus-treated samples. This negative response of OTUs to virus amendment probably was caused by viral lysis. Additionally, we found OTUs not responding to the amendments, and several OTUs exhibited variable responses to the addition of inactive or active viruses. Therefore, we conclude that individual members of pelagic archaeal and bacterial communities can be differently affected by the presence of virioplankton.

Animals↗

PubMed2002

Simultaneous extraction from bacterioplankton of total RNA and DNA suitable for quantitative structure and function analyses.

The aim of this study was to develop a protocol for the simultaneous extraction from bacterioplankton of RNA and DNA suitable for quantitative molecular analysis. By using a combined mechanical and chemical extraction method, the highest RNA and DNA yield was obtained with sodium lauryl sarcosinate-phenol or DivoLab-phenol as the extraction mix. The efficiency of extraction of nucleic acids was comparatively high and varied only moderately in gram-negative bacterial isolates and bacterioplankton (RNA, 52 to 66%; DNA, 43 to 61%); significant amounts of nucleic acids were also obtained for a gram-positive bacterial isolate (RNA, 20 to 30%; DNA, 20 to 25%). Reverse transcription-PCR and PCR amplification products of fragments of 16S rRNA and its genes were obtained from all isolates and communities, indicating that the extracted nucleic acids were intact and pure enough for community structure analyses. By using single-strand conformation polymorphism of fragments of 16S rRNA and its gene, community fingerprints were obtained from pond bacterioplankton. mRNA transcripts encoding fragments of the enzyme nitrite reductase gene (nir gene) could be detected in a pond water sample, indicating that the extraction method is also suitable for studying gene expression. The extraction method presented yields nucleic acids that can be used to perform structural and functional studies of bacterioplankton communities from a single sample.

Animals↗