Seasonal Dynamics of Methanotrophic Bacteria in a Boreal Oil Sands End Pit Lake.

Base Mine Lake (BML) is the first full-scale demonstration end pit lake for the oil sands mining industry in Canada. We examined aerobic methanotrophic bacteria over all seasons for 5 years in this dimictic lake. Methanotrophs comprised up to 58% of all bacterial reads in 16S rRNA gene amplicon sequencing analyses (median 2.8%), and up to 2.7 × 104 cells mL-1 of water (median 0.5 × 103) based on qPCR of pmoA genes. Methanotrophic activity and populations in the lake water were highest during fall turnover and remained high through the winter ice-covered period into spring turnover. They declined during summer stratification, especially in the epilimnion. Three methanotroph genera (Methylobacter, Methylovulum, and Methyloparacoccus) cycled seasonally, based on both relative and absolute abundance measurements. Methylobacter and Methylovulum populations peaked in winter/spring, when methane oxidation activity was psychrophilic. Methyloparacoccus populations increased in the water column through summer and fall, when methane oxidation was mesophilic, and also predominated in the underlying tailings sediment. Other, less abundant genera grew primarily during summer, possibly due to distinct CH4/O2 microniches created during thermal stratification. These data are consistent with temporal and spatial niche differentiation based on temperature, CH4 and O2. This pit lake displays methane cycling and methanotroph population dynamics similar to natural boreal lakes. IMPORTANCE The study examined methanotrophic bacteria in an industrial end pit lake, combining molecular DNA methods (both quantitative and descriptive) with biogeochemical measurements. The lake was sampled over 5 years, in all four seasons, as often as weekly, and included sub-ice samples. The resulting multiseason and multiyear data set is unique in its size and intensity, and allowed us to document clear and consistent seasonal patterns of growth and decline of three methanotroph genera (Methylobacter, Methylovulum, and Methyloparacoccus). Laboratory experiments suggested that one major control of this succession was niche partitioning based on temperature. The study helps to understand microbial dynamics in engineered end pit lakes, but we propose that the dynamics are typical of boreal stratified lakes and widely applicable in microbial ecology and limnology. Methane-oxidizing bacteria are important model organisms in microbial ecology and have implications for global climate change.

Analysis of microbial communities in natural halite springs reveals a domain-dependent relationship of species diversity to osmotic stress.

Microbial species diversity may peak at certain optimal environmental conditions and decrease toward more extreme conditions. Indeed, bell-shaped relationships of species diversity against pH and temperature have been demonstrated, but diversity patterns across other environmental conditions are less well reported. In this study, we investigated the impact of salinity on the diversity of microorganisms from all three domains in a large set of natural springs with salinities ranging from freshwater to halite saturated. Habitat salinity was found to be linearly and inversely related to diversity of all three domains. The relationship was strongest in the bacteria, where salinity explained up to 44% of the variation in different diversity metrics (OTUs, Shannon index, and Phylogenetic Diversity). However, the relationship was weaker for Eukarya and Archaea. The known salt-in strategist Archaea of the Halobacteriaceae even showed the opposite trend, with increasing diversity at higher salinity. We propose that high energetic requirements constrain species diversity at high salinity but that the diversity of taxa with energetically less expensive osmotolerance strategies is less affected. Declining diversity with increasing osmotic stress may be a general rule for microbes as well as plants and animals, but the strength of this relationship varies greatly across microbial taxa.

Emended description of the family Beijerinckiaceae and transfer of the genera Chelatococcus and Camelimonas to the family Chelatococcaceae fam. nov.

The family Beijerinckiaceae was circumscribed in 2005 to accommodate four genera of phylogenetically related alphaproteobacteria: Beijerinckia, Chelatococcus, Methylocella and Methylocapsa. Later, four additional genera, i.e. Methylovirgula, Methyloferula, Methylorosula and Camelimonas, were described and assigned to this family, which now accommodates 21 species with validly published names. Members of this family possess strikingly different lifestyles, including chemoheterotrophy, facultative methylotrophy, obligate methanotrophy and facultative methanotrophy. Levels of 16S rRNA gene sequence similarity among most of these bacteria range from 96 to 98 %, suggesting a common evolutionary origin. The genera Chelatococcus and Camelimonas, however, are not monophyletic with the other described genera based on 16S rRNA gene sequence phylogeny, and instead form a distant cluster more closely related to the Methylobacteriaceae. Physiologically these two genera also lack several properties common to the other Beijerinckiaceae. On the other hand, the genus Rhodoblastus, presently considered a member of the Bradyrhizobiaceae, affiliates with high confidence to the Beijerinckiaceae. Here, we propose to transfer the genera Chelatococcus and Camelimonas to the family Chelatococcaceae fam. nov., and present an emended description of the family Beijerinckiaceae, including the genus Rhodoblastus.