Eva S. Lindström

THE ROLE OF ENVIRONMENTAL AND SPATIAL PROCESSES IN STRUCTURING LAKE COMMUNITIES FROM BACTERIA TO FISH

We assessed the relative roles of local environmental conditions and dispersal on community structure in a landscape of lakes for the major trophic groups. We use taxonomic presence-absence and abundance data for bacteria, phytoplankton, zooplankton, and fish from 18 lakes in southern Quebec, Canada. The question of interest was whether communities composed of organisms with more limited dispersal abilities, because of size and life history (zooplankton and fish) would show a different effect of lake distribution than communities composed of good dispersers (bacteria and phytoplankton). We examine the variation in structure attributable to local environmental (i.e., lake chemical and physical variables) vs. dispersal predictors (i.e., overland and watercourse distances between lakes) using variation partitioning techniques. Overall, we show that less motile species (crustacean zooplankton and fish) are better predicted by spatial factors than by local environmental ones. Furthermore, we show that for zooplankton abundances, both overland and watercourse dispersal pathways are equally strong, though they may select for different components of the community, while for fish, only watercourses are relevant dispersal pathways. These results suggest that crustacean zooplankton and fish are more constrained by dispersal and therefore more likely to operate as a metacommunity than are bacteria and phytoplankton within this studied landscape.

Distribution of typical freshwater bacterial groups is associated with pH, temperature and lake water retention time

ABSTRACT The distribution of 15 typical freshwater bacterial groups in 15 diverse lakes in northern Europe was investigated using reverse line blot hybridization. Statistical evaluation of the data in relation to the characteristics of the lakes showed that pH, temperature, and the theoretical hydrological retention time of the lakes were most strongly related to variations in the distribution of bacterial taxa. This suggests that pH and temperature are steering factors in the selection of taxa and supports the notion that communities in lakes with short water turnover times are influenced by the input of bacterial cells from the drainage areas. Within the beta subdivision of the Proteobacteria (Betaproteobacteria), as well as within the divisions Actinobacteria and Verrucomicrobia, different subgroups were associated differently with environmental variables.

Local and regional factors influencing bacterial community assembly

The classical view states that microbial biogeography is not affected by dispersal barriers or historical events, but only influenced by the local contemporary habitat conditions (species sorting). This has been challenged during recent years by studies suggesting that also regional factors such as mass effect, dispersal limitation and neutral assembly are important for the composition of local bacterial communities. Here we summarize results from biogeography studies in different environments, i.e. in marine, freshwater and soil as well in human hosts. Species sorting appears to be the most important mechanism. However, this result might be biased since this is the mechanism that is easiest to measure, detect and interpret. Hence, the importance of regional factors may have been underestimated. Moreover, our survey indicates that different assembly mechanisms might be important for different parts of the total community, differing, for example, between generalists and specialists, and between taxa of different dispersal ability and motility. We conclude that there is a clear need for experimental studies, first, to clearly separate regional and local factors in order to study their relative importance, and second, to test whether there are differences in assembly mechanisms depending on different taxonomic or functional groups.

SCID II interviews and the SCID Screen questionnaire as diagnostic tools for personality disorders in DSM-III-R

A modified version of the SCID Screen questionnaire covering 103 criteria by means of 124 questions was compared with SCID II interviews in 69 psychiatric patients. The correlation between the number of criteria fulfilled in the SCID II interviews or the questionnaires was 0.84. In the SCID interviews, 54% of the patients had a personality disorder. When the SCID Screen questionnaire was used, 73% had a personality disorder. When the cut‐off level for diagnosis was adjusted, the frequency found by means of the SCID screen questionnaire or the interviews was roughly the same, 58% and 54%, respectively. The overall kappa for agreement between the SCID II interviews and questionnaire with adjusted cut‐off was 0.78.

Bacterioplankton Community Composition in Five Lakes Differing in Trophic Status and Humic Content.

A bstractTo investigate the relation between lake type and bacterioplankton community composition, five Swedish lakes, which differed from each other in nutrient content and water color, were studied. Denaturing gradient gel electrophoresis (DGGE) of 16S rDNA was used to examine community composition. The DGGE-patterns of the different samples were analyzed in relation to physical, chemical, and biological data from the lakes by canonical correspondence analysis (CCA). The three variables found to most strongly correlate with the DGGE patterns were biomasses of microzooplankton, cryptophytes, and chrysophytes, suggesting that these biota had an impact on bacterioplankton community structure. Two of the three factors were, in turn, significantly correlated to parameters associated with the trophic status of the lakes, indicating that the nutrient content of the lakes, at least indirectly, influenced the structure of the bacterioplankton community. The relation to water color was less pronounced.

Unraveling assembly of stream biofilm communities.

Microbial biofilms assemble from cells that attach to a surface, where they develop into matrix-enclosed communities. Mechanistic insights into community assembly are crucial to better understand the functioning of natural biofilms, which drive key ecosystem processes in numerous aquatic habitats. We studied the role of the suspended microbial community as the source of the biofilm community in three streams using terminal-restriction fragment length polymorphism and 454 pyrosequencing of the 16S ribosomal RNA (rRNA) and the 16S rRNA gene (as a measure for the active and the bulk community, respectively). Diversity was consistently lower in the biofilm communities than in the suspended stream water communities. We propose that the higher diversity in the suspended communities is supported by continuous inflow from various sources within the catchment. Community composition clearly differed between biofilms and suspended communities, whereas biofilm communities were similar in all three streams. This suggests that biofilm assembly did not simply reflect differences in the source communities, but that certain microbial groups from the source community proliferate in the biofilm. We compared the biofilm communities with random samples of the respective community suspended in the stream water. This analysis confirmed that stochastic dispersal from the source community was unlikely to shape the observed community composition of the biofilms, in support of species sorting as a major biofilm assembly mechanism. Bulk and active populations generated comparable patterns of community composition in the biofilms and the suspended communities, which suggests similar assembly controls on these populations.

Biogeography of bacterial communities exposed to progressive long-term environmental change

The response of microbial communities to long-term environmental change is poorly understood. Here, we study bacterioplankton communities in a unique system of coastal Antarctic lakes that were exposed to progressive long-term environmental change, using 454 pyrosequencing of the 16S rDNA gene (V3–V4 regions). At the time of formation, most of the studied lakes harbored marine-coastal microbial communities, as they were connected to the sea. During the past 20 000 years, most lakes isolated from the sea, and subsequently they experienced a gradual, but strong, salinity change that eventually developed into a gradient ranging from freshwater (salinity 0) to hypersaline (salinity 100). Our results indicated that present bacterioplankton community composition was strongly correlated with salinity and weakly correlated with geographical distance between lakes. A few abundant taxa were shared between some lakes and coastal marine communities. Nevertheless, lakes contained a large number of taxa that were not detected in the adjacent sea. Abundant and rare taxa within saline communities presented similar biogeography, suggesting that these groups have comparable environmental sensitivity. Habitat specialists and generalists were detected among abundant and rare taxa, with specialists being relatively more abundant at the extremes of the salinity gradient. Altogether, progressive long-term salinity change appears to have promoted the diversification of bacterioplankton communities by modifying the composition of ancestral communities and by allowing the establishment of new taxa.

Structure and function of bacterial communities emerging from different sources under identical conditions.

ABSTRACT The aim of this study was to compare two major hypotheses concerning the formation of bacterial community composition (BCC) at the local scale, i.e., whether BCC is determined by the prevailing local environmental conditions or by “metacommunity processes.” A batch culture experiment where bacteria from eight distinctly different aquatic habitats were regrown under identical conditions was performed to test to what extent similar communities develop under similar selective pressure. Differently composed communities emerged from different inoculum communities, as determined by terminal restriction fragment length polymorphism analysis of the 16S rRNA gene. There was no indication that similarity increased between communities upon growth under identical conditions compared to that for growth at the ambient sampling sites. This suggests that the history and distribution of taxa within the source communities were stronger regulating factors of BCC than the environmental conditions. Moreover, differently composed communities were different with regard to specific functions, such as enzyme activities, but maintained similar broad-scale functions, such as biomass production and respiration.

Function-specific response to depletion of microbial diversity.

Recent meta-analyses suggest that ecosystem functioning increases with biodiversity, but contradictory results have been presented for some microbial functions. Moreover, observations of only one function underestimate the functional role of diversity because of species-specific trade-offs in the ability to carry out different functions. We examined multiple functions in batch cultures of natural freshwater bacterial communities with different richness, achieved by a dilution-to-extinction approach. Community composition was assessed by molecular fingerprinting of 16S rRNA and chitinase genes, representing the total community and a trait characteristic for a functional group, respectively. Richness was positively related to abundance and biomass, negatively correlated to cell volumes and unrelated to maximum intrinsic growth rate. The response of chitin and cellulose degradation rates depended on the presence of a single phylotype. We suggest that species identity and community composition rather than richness matters for specific microbial processes.

Autistic traits in obsessive-compulsive disorder

In contrast to other non-psychotic psychiatric populations, subjects with obsessive-compulsive disorder (OCD) are more prone to have personality disorder from cluster A (the odd and eccentric cluster). The present study aims at further investigating the relationship between these and other personality traits in OCD subjects and their relation to high functioning autism (HFA) and Asperger disorder. Sixty-four subjects with OCD were included. Personality traits were assessed with the Karolinska Scales of Personality (KSP), and personality disorders with DSM-adapted questionnaires. In addition, autistic traits were assessed in 29 videotaped subjects, by 3 independent raters. Twenty percent of the subjects with OCD were identified as also having autistic traits. These subjects scored higher on KSP scales measuring muscular tension, psychasthenia, and inhibition of aggression and lower on socialization as compared with OCD subjects without autistic traits. Additionally, subjects with autistic traits fulfilled criteria for anxious personality disorders and paranoid personality disorders significantly more often than subjects without autistic traits. We propose that OCD is often related to HFA and Asperger disorder. Self-report questionnaires may be useful in establishing the diagnosis. However, those with the most obvious autistic features seem to be less able to identify these traits in themselves.In contrast to other non-psychotic psychiatric populations, subjects with obsessive-compulsive disorder (OCD) are more prone to have personality disorder from cluster A (the odd and eccentric cluster). The present study aims at further investigating the relationship between these and other personality traits in OCD subjects and their relation to high functioning autism (HFA) and Asperger disorder. Sixty-four subjects with OCD were included. Personality traits were assessed with the Karolinska Scales of Personality (KSP), and personality disorders with DSM-adapted questionnaires. In addition, autistic traits were assessed in 29 videotaped subjects, by 3 independent raters. Twenty percent of the subjects with OCD were identified as also having autistic traits. These subjects scored higher on KSP scales measuring muscular tension, psychasthenia, and inhibition of aggression and lower on socialization as compared with OCD subjects without autistic traits. Additionally, subjects with autistic traits fulfilled criteria for anxious personality disorders and paranoid personality disorders significantly more often than subjects without autistic traits. We propose that OCD is often related to HFA and Asperger disorder. Self-report questionnaires may be useful in establishing the diagnosis. However, those with the most obvious autistic features seem to be less able to identify these traits in themselves.