Thermal and chemical disinfection of water and biofilms: only a temporary effect in regard to the autochthonous bacteria.

Thermal and chemical disinfection of technical water systems not only aim at minimizing the level of undesired microorganisms, but also at preventing excessive biofouling, clogging and interference with diverse technical processes. Typically, treatment has to be repeated in certain time intervals, as the duration of the effect is limited. The transient effect of disinfection was demonstrated in this study applying different treatments to water and biofilms including heat, chlorination, a combination of hydrogen peroxide and peracetic acid and monochloramine. Despite the diverse treatments, the reduction in live bacteria was followed by regrowth in all cases, underlining the universal validity of this phenomenon. The study shows that autochthonous bacteria can reach the concentrations given prior to treatment. The reason is seen in the nutrient concentration that has not changed and that forms the basis for regrowth. Nutrients are released by disinfection from lysed cells or are still fixed in dead biomass that is subsequently scavenged by necrotrophic growth. Treatment cycles therefore only provide a transient reduction of water microbiology if nutrients are not removed. When aiming at greater sustainability of the effect, biocidal treatment has to be equally concerned about nutrient removal by subsequent cleaning procedures as about killing efficiency.

The D-A-(C) index: A practical approach towards the microbiological-ecological monitoring of groundwater ecosystems.

Groundwater is not only a vital resource, but also one of the largest terrestrial aquatic ecosystems on Earth. However, to date, ecological criteria are often not considered in routine groundwater monitoring, mainly because of the lack of suitable ecological assessment tools. Prokaryotic microorganisms are ubiquitous in groundwater ecosystems even under the harshest conditions, making them ideal bioindicators for ecological monitoring. We have developed a simple, inexpensive approach that enables ecological groundwater monitoring based on three microbiological parameters that can be easily integrated into existing routine monitoring practices: prokaryotic cell density (D) measured by flow cytometry; activity (A) measured as prokaryotic intracellular ATP concentrations using a simple cell-lysis-luminescence assay; and, as an optional parameter, the bioavailable carbon (C) measured as the concentration of assimilable organic carbon in a simple batch growth assay. We analyzed data for three case studies of different disturbances representing some of the main threats to groundwater ecosystems, i.e. organic contamination with hydrocarbons, surface water intrusion, and agricultural land use. For all three disturbances, disturbed samples could be reliably distinguished from undisturbed samples based on a single index value obtained from multivariate outlier analyses of the microbial variables. We could show that this multivariate approach allowed for a significantly more sensitive and reliable detection of disturbed samples compared to separate univariate outlier analyses of the measured variables. Furthermore, a comparison of non-contaminated aquifers from nine different regions across Germany revealed distinct multivariate signatures along the three microbial variables, which should be considered when applying our approach in practice. In essence, our approach offers a practical tool for the detection of disturbances of groundwater ecosystems based on microbial parameters which can be seamlessly extended in the future by additional parameters for higher sensitivity as well as flexibility.

Complete nitrification by Nitrospira bacteria.

Nitrification, the oxidation of ammonia via nitrite to nitrate, has always been considered to be a two-step process catalysed by chemolithoautotrophic microorganisms oxidizing either ammonia or nitrite. No known nitrifier carries out both steps, although complete nitrification should be energetically advantageous. This functional separation has puzzled microbiologists for a century. Here we report on the discovery and cultivation of a completely nitrifying bacterium from the genus Nitrospira, a globally distributed group of nitrite oxidizers. The genome of this chemolithoautotrophic organism encodes the pathways both for ammonia and nitrite oxidation, which are concomitantly activated during growth by ammonia oxidation to nitrate. Genes affiliated with the phylogenetically distinct ammonia monooxygenase and hydroxylamine dehydrogenase genes of Nitrospira are present in many environments and were retrieved on Nitrospira-contigs in new metagenomes from engineered systems. These findings fundamentally change our picture of nitrification and point to completely nitrifying Nitrospira as key components of nitrogen-cycling microbial communities.

Cohn's Crenothrix is a filamentous methane oxidizer with an unusual methane monooxygenase.

135 years ago Ferdinand Cohn, the founder of bacteriology, microscopically observed a conspicuous filamentous bacterium with a complex life cycle and described it as Crenothrix polyspora. This uncultured bacterium is infamous for mass developments in drinking water systems, but its phylogeny and physiology remained unknown. We show that C. polyspora is a gammaproteobacterium closely related to methanotrophs and capable of oxidizing methane. We discovered that C. polyspora encodes a phylogenetically very unusual particulate methane monooxygenase whose expression is strongly increased in the presence of methane. Our findings demonstrate a previously unrecognized complexity of the evolutionary history and cell biology of methane-oxidizing bacteria.