Diversity Of Bacterial Populations Research Articles

Denaturing gradient gel electrophoresis used to monitor the enrichment culture of aerobic chemoorganotrophic bacteria from a hot spring cyanobacterial mat.

Previous studies investigating microbial diversity in the Octopus Spring cyanobacterial mat community (Yellowstone National Park) have shown a discrepancy between bacterial populations observed by molecular retrieval and cultivation techniques. To investigate how selective enrichment culture techniques affect species composition, we used denaturing gradient gel electrophoresis (DGGE) separation of PCR-amplified 16S rRNA gene fragments to monitor the populations contained within enrichment cultures of aerobic chemoorganotrophic bacteria from the ca. 50 degrees C region of the mat community. By varying the degree of dilution of the inoculum, medium composition, and enrichment conditions and duration and by analyzing the cultures by DGGE, we detected 14 unique 16S rRNA sequence types. These corresponded to alpha-, beta-, gamma-, and delta-proteobacteria, Thermus relatives, and gram-positive bacteria with high G + C ratio and, at the highest inoculum dilutions, Chloroflexus aurantiacus relatives, which were estimated to still be approximately 300 times less abundant than cells of the mat primary producer, Synechococcus spp. Only three of these populations were previously cultivated on solidified medium after similar enrichment. Only two of these population have 16S rRNA sequences which were previously cloned directly from the mat. These results reveal a diversity of bacterial populations in enrichment culture which were not detected by either molecular retrieval or strain purification techniques.

Genome size in bacteria.

This manuscript examines genome size in bacteria. The opposing capability of bacteria to alter their genome sizes and order of genes within limits yet remain somewhat constant provides a mechanisms for diversity and evolution in bacterial populations. Bacteria may have evolved by increasing their genome size and changing gene orders with the assistance of restriction endonucleases cleaving foreign DNA and providing a diverse pool of DNA sequences for recombination. These aspects and selected information on physically mapping bacterial genomes will be discussed.

Potential risks of gene amplification by PCR as determined by 16S rDNA analysis of a mixed-culture of strict barophilic bacteria

The 16S rDNA genes of an apparently pure culture of a psychrophilic and strict barophilic bacterium (WHB 46) were studied by PCR-mediated amplification and cloning into phage M13 mp18. Sequence analysis of five individual clones revealed the presence of two different 16S rDNA types. The homology value of 90% indicates that culture WHB 46 is actually composed of two closely related species (WHB 46-1 and 46-2). Both strains are members of the γ-subdivision of proteobacteria. Analysis of a sixth clone (WHB 46-1/2) leads to the conclusion that it represents a 16S rDNA hybrid molecule assembled during the PCR reaction. This hypothesis was confirmed by secondary structure analysis of the chimeric rDNA. The appearance of such hybrid molecules point to a potential risk in studies on the diversity of bacterial populations by analysis of rDNA pattern via PCR-mediated amplification because they suggest the existence of organisms that do not actually exist in the sample investigated.

Characteristics and diversity of subarctic marine oligotrophic, stenoheterotrophic, and euryheterotrophic bacterial populations

Major differences were found in the characteristics of bacterial populations isolated on media containing high and low nutrient concentrations. Bacteria isolated on low-nutrient media were physiologically more tolerant and nutritionally more versatile than bacteria isolated on high-nutrient media. It appears that euryheterotrophy, as opposed to oligotrophy, is characteristic of subarctic marine bacterial populations capable of growing at low nutrient concentrations. The bacteria examined in this study were capable of growth under a wide variety of physiological and nutritional conditions. The isolates from high-nutrient media were somewhat more specialized than those isolated from low-nutrient media. While the physiological and metabolic capabilities of the bacterial populations isolated on low-nutrient media were very heterogeneous, their taxonomic diversity was lower than bacterial populations from high-nutrient isolation media. The inclusion of petroleum in the isolation media did not alter the characteristics of the isolates obtained from either high- or low-nutrient media.

Structure, diversity, and catabolic potentialities of aerobic heterotrophic bacterial populations associated with continuous cultures of natural marine phytoplankton

Variations of structure (probable taxonomic generic groups; ecological profiles), diversity (Shannon index, ¯H), and average catabolic potentialities (strain's average exoenzyme equipment, EAI; average carbonaceous compound utilization, UAI) of bacterial populations during two experimental phytoplankton blooms are described and show a certain overall unity. Oligotrophic conditions are characterized by high diversity levels (¯H from 3.60 to 4) and moderate catabolic potentialities (EAI and UAI close to 40%). During phytoplankton exponential growth phase bacteria show an EAI stability, but there is an increase of UAI with maximal values at the beginning of chlorophyll plateau (52-57%) and higher values of diversity (¯H greater than 4). Phytoplankton mortalities appear to cause an EAI increase and a decrease of both UAI and ¯H (1.50 to 2). Vibrio-like organisms seem to be closely related to this period.In spite of these similar patterns, many differences appear between both experiments from a taxonomic point of view, the autumnal population being more diversified than the spring one.The results obtained show the value of simultaneous analysis of these different aspects and of this ecological methodology allowing spatial or temporal comparisons.

Diversity of bacterial populations in the Beaufort Sea

BIOLOGICAL communities usually contain few species with many individuals and many species with few individuals1. Diversity of higher organisms generally has been found to decrease with increasing population size1. Communities in physically stressed ecosystems, such as in polar regions, characteristically have low species diversity2. Diversity indices have been used to express species diversity in plant and animal communities, especially as a measure of stress on community structure2. Amongst microorganisms, diversity indices have been applied to microscopic phytoplankton populations3,4, but not to bacterial populations. Bacterial populations, however, show large variations in species diversity. For example, infections are dominated by one or a few species, whereas many bacterial species are found in an ecosystem such as soil5. We report here the application of taxonomic diversity indices to bacterial populations and a study of the relationship of the diversity indices of such populations to population size and to population-independent factors such as geographic location.