Persistent activity of aerobic methane-oxidizing bacteria in anoxic lake waters due to metabolic versatility.

Lacustrine methane emissions are strongly mitigated by aerobic methane-oxidizing bacteria (MOB) that are typically most active at the oxic-anoxic interface. Although oxygen is required by the MOB for the first step of methane oxidation, their occurrence in anoxic lake waters has raised the possibility that they are capable of oxidizing methane further anaerobically. Here, we investigate the activity and growth of MOB in Lake Zug, a permanently stratified freshwater lake.

Diverse methylotrophic methanogenic archaea cause high methane emissions from seagrass meadows.

Marine coastlines colonized by seagrasses are a net source of methane to the atmosphere. However, methane emissions from these environments are still poorly constrained, and the underlying processes and responsible microorganisms remain largely unknown. Here, we investigated methane turnover in seagrass meadows of in the Mediterranean Sea.

Terrestrial-type nitrogen-fixing symbiosis between seagrass and a marine bacterium.

Symbiotic N-fixing microorganisms have a crucial role in the assimilation of nitrogen by eukaryotes in nitrogen-limited environments. Particularly among land plants, N-fixing symbionts occur in a variety of distantly related plant lineages and often involve an intimate association between host and symbiont. Descriptions of such intimate symbioses are lacking for seagrasses, which evolved around 100 million years ago from terrestrial flowering plants that migrated back to the sea.

Anaerobic endosymbiont generates energy for ciliate host by denitrification.

Mitochondria are specialized eukaryotic organelles that have a dedicated function in oxygen respiration and energy production. They evolved about 2 billion years ago from a free-living bacterial ancestor (probably an alphaproteobacterium), in a process known as endosymbiosis. Many unicellular eukaryotes have since adapted to life in anoxic habitats and their mitochondria have undergone further reductive evolution.

sp. nov., a Chemolithoheterotroph Isolated from Sulfide- and Organic-Rich Coastal Waters off Peru.

Members of the epsilonproteobacterial genus have been identified to be potentially important sulfide oxidizers in marine coastal, seep, and stratified basin environments. In the highly productive upwelling waters off the coast of Peru, cells comprised 3 to 25% of the total microbial community at a near-shore station where sulfide concentrations exceeded 20 μM in bottom waters. From the chemocline where the population exceeded 10 cells ml and where high rates of denitrification (up to 6.

Bloom of a denitrifying methanotroph, 'Candidatus Methylomirabilis limnetica', in a deep stratified lake.

Methanotrophic bacteria represent an important biological filter regulating methane emissions into the atmosphere. Planktonic methanotrophic communities in freshwater lakes are typically dominated by aerobic gamma-proteobacteria, with a contribution from alpha-proteobacterial methanotrophs and the NC10 bacteria. The NC10 clade encompasses methanotrophs related to 'Candidatus Methylomirabilis oxyfera', which oxidize methane using a unique pathway of denitrification that tentatively produces N and O from nitric oxide (NO).

Crenothrix are major methane consumers in stratified lakes.

Methane-oxidizing bacteria represent a major biological sink for methane and are thus Earth's natural protection against this potent greenhouse gas. Here we show that in two stratified freshwater lakes a substantial part of upward-diffusing methane was oxidized by filamentous gamma-proteobacteria related to Crenothrix polyspora. These filamentous bacteria have been known as contaminants of drinking water supplies since 1870, but their role in the environmental methane removal has remained unclear.