Oligotrophic ecosystems can be loosely defined as environments that exhibit low ambient nutrient levels. During my thesis, I used 454 DNA pyrosequencing of partial 16S rDNA to explore the bacterial diversity in three different oligotrophic environments, including A. surface desert soil, B. Asian sandstorm dust and C. a section of the city of Paris’s drinking water distribution system.A. Arid regions represent nearly 30% of the Earth’s terrestrial surface. The living conditions at the surface of deserts are a challenge for microorganisms, as there is little available water and/or carbon, a very large range of temperatures and high exposure to UV irradiation from the Sun. In surface sand samples from two large Asian deserts, unexpectedly large bacterial diversity residing was revealed. Sequences belonging to the Firmicutes, Proteobacteria, Bacteroidetes and Actinobacteria phyla were the most abundant. An increase in phylotype numbers with increasing C/N ratio was noted, suggesting a possible role in the bacterial richness of these desert sand environments.B. Desert sandstorms are a meteorological phenomenon which have been postulated affect the Earth's climate and public health. We examined the particle-associated (dust and sand-associated) bacterial populations of atmospheric sand in the absence (as control) and presence of sandstorms in five Asian cities. Greater than 90% of the sequences can be classified as representing bacteria belonging to four phyla: Proteobacteria, Bacteriodetes, Actinobacteria and Firmicutes. Principal component analyses showed that the sandstorm-associated bacterial populations were clustered by sampling year, rather than location. Members belonging to nine bacterial genera (Massilia, Planococcus, Carnobacterium, Planomicrobium, Pontibacter, Pedobacter, Lysobacter, Sanguibacter, Ohtaekwangia) were observed to increase in sand-associated samples from sandstorms, versus the controls. C. We characterized the bacterial communities in three water and three biofilm samples from one part of the Parisian drinking water distribution system. A dramatic change in bacterial population in the water during flow through the distribution system from the water treatment plant to the exit from the reservoir was found. The richness of the bacterial population was reduced from the water treatment plant to the reservoir (from 336 to 165 OTUs for water samples leaving the reservoir and from 947 to 275 for biofilm samples in the network). Several OTUs belonging to pathogenic genera were detected in our samples, mostly in the biofilm samples, thus suggesting that the biofilms may be an important source of bacteria during water distribution to the consumers.
Characterization of bacterial diversity in three oligotrophic environments using high-throughput sequencing technology