Detritus-Dependent Development of the Microbial Community in an Experimental System: Qualitative Analysis by Denaturing Gradient Gel Electrophoresis

Abstract

Correlations between the biomass of phytoplankton and the biomass of bacteria and between the biomass of bacteria and the biomass of protozoans suggest that there is coupling between these compartments of the “microbial loop.” To investigate this coupling on the species level, bacteria and protozoans from untreated lake water inocula were allowed to grow on detritus of the green alga Ankistrodesmus falcatus or the cyanobacterium Oscillatoria limneticain continuous-flow systems for 1 month. Denaturing gradient gel electrophoresis (DGGE) of the 16S and 18S rRNA genes was used to monitor the development of the bacterial community structure and the eukaryotic community structure, respectively. Nonmetric multidimensional scaling of the DGGE profiles revealed the changes in the microbial community structure. This analysis showed that significantly different bacterial communities developed on the green algal detritus and on the cyanobacterial detritus. Although similar results were obtained for the eukaryotic communities, the differences were not significant. Hence, our findings indicate that the origin of detritus can affect the structure of at least the bacterial community. A phylogenetic analysis of 20 18S ribosomal DNA clones that were isolated from the continuous cultures revealed that many sequences were related to the sequences of bacterivorous protozoans (members of the Ciliophora, Rhizopoda, Amoeba, and Kinetoplastida). One clone grouped in a recently established clade whose previously described members are all parasites. The affiliations of about 20% of the clones could not be determined.

Marine diatom species harbour distinct bacterial communities

“…It is well known that this transition in algal growth leads to changes in quantity and quality of organic matter of algal origin (Brockmann et al, 1979). The succession of the bacterial community in relation to changes in the organic matter field during a phytoplankton bloom has been previously reported (van Hannen et al, 1999;Riemann et al, 2000;Fandino et al, 2001). In addition, our results indicate that distinct successions of bacterial communities differ in the surrounding water and on algal particles and greatly vary among different algal species.…”

“…Numbers of bacteria on senescent algae were even up to two orders of magnitude higher than on exponentially growing algae (Verity et al ., 1988). More recent studies on bacterial community composition in the course of phytoplankton blooms in mesocosm experiments as well as in the field also revealed close relationships between the bacterial community structure and the composition, growth and physiological status of phytoplankton (van Hannen et al ., 1999;Pinhassi and Hagström, 2000;Riemann et al ., 2000;Zubkov et al ., 2001).…”

Impact of lower salinity waters on bacterial heterotrophic production and community structure in the offshore NW Mediterranean Sea

“…Different sources of freshwater DOC were also shown to have an important impact on bacterial activity and community composition (Kirchman et al, 2004;Rochelle-Newall et al, 2004). The origin of DOM with respect to a particular phytoplankton species influenced significantly bacterial community structure in continuous flow systems that had been inoculated with either cyanobacterial or algal detritus (van Hannen et al, 1999). These observations suggest that specialized bacterial groups use DOC sources that vary most likely with respect to their chemical composition (Cottrell et al, 2005;Bauer et al, 2006).…”

The molecular diversity of freshwater picoeukaryotes from an oligotrophic lake reveals diverse, distinctive and globally dispersed lineages

“…An accurate record of eukaryotic microbial diversity is a key to resolving evolutionary relationships, as well as understanding a range of biological and environmental factors such as community assembly, the effects of local habitat catastrophe, environmental change, and the biological components of ecological processes. While traditional methods for sampling microbial communities have limited capacity in elucidating true environmental microbial diversity and are often biased towards species with morphologically distinctive features (Pace, 1997), environmental gene libraries of small subunit ribosomal RNA have consistently demonstrated that natural microbial diversity is far more extensive than has previously been observed (van Hannen et al ., 1999;Lopez-Garcia et al ., 2001;Moon-van der Staay et al ., 2001;Amaral Zettler et al ., 2002;Dawson and Pace, 2002;Edgcomb et al ., 2002;Moreira and Lopez-Garcia, 2002;Lopez-Garcia et al ., 2003). It has also become clear that the existing 18S rDNA catalogue is missing ecologically significant morphospecies and requires sampling from alternative environments (Lopez-Garcia et al ., 2001;Dawson and Pace, 2002;Stoeck and Epstein, 2003).…”

“…There are approximately 250 000 cubic kilometers of freshwater on earth, in the forms of lakes, inland seas and rivers, all of which potentially harbour as diverse an assemblage of eukaryotic microbes as has been discovered in open oceans (Guillou et al ., 1999;Diez et al ., 2001a,b;Lopez-Garcia et al ., 2001;Moon-van der Staay et al ., 2001). However, rRNA sequence data from freshwater are limited to environments of acidic pH (Amaral Zettler et al ., 2002) and freshwater microbial communities maintained in a model system and nourished by specific microbial monocultures (van Hannen et al ., 1999). Consequently, the diversity, distribution and natural abundance of different freshwater eukaryotic microbial taxa are largely unknown.…”