Martin Hesselsøe

Bio: Martin Hesselsøe is an academic researcher from Aalborg University. The author has contributed to research in topics: Nitrosomonas europaea & Marine Strategy Framework Directive. The author has an hindex of 18, co-authored 34 publications receiving 1323 citations.

The isotope array, a new tool that employs substrate-mediated labeling of rRNA for determination of microbial community structure and function.

Abstract: A new microarray method, the isotope array approach, for identifying microorganisms which consume a 14C-labeled substrate within complex microbial communities was developed. Experiments were performed with a small microarray consisting of oligonucleotide probes targeting the 16S rRNA of ammonia-oxidizing bacteria (AOB). Total RNA was extracted from a pure culture of Nitrosomonas eutropha grown in the presence of [14C]bicarbonate. After fluorescence labeling of the RNA and microarray hybridization, scanning of all probe spots for fluorescence and radioactivity revealed that specific signals were obtained and that the incorporation of 14C into rRNA could be detected unambiguously. Subsequently, we were able to demonstrate the suitability of the isotope array approach for monitoring community composition and CO2 fixation activity of AOB in two nitrifying activated-sludge samples which were incubated with [14C]bicarbonate for up to 26 h. AOB community structure in the activated-sludge samples, as predicted by the microarray hybridization pattern, was confirmed by quantitative fluorescence in situ hybridization (FISH) and comparative amoA sequence analyses. CO2 fixation activities of the AOB populations within the complex activated-sludge communities were detectable on the microarray by 14C incorporation and were confirmed independently by combining FISH and microautoradiography. AOB rRNA from activated sludge incubated with radioactive bicarbonate in the presence of allylthiourea as an inhibitor of AOB activity showed no incorporation of 14C and thus was not detectable on the radioactivity scans of the microarray. These results suggest that the isotope array can be used in a PCR-independent manner to exploit the high parallelism and discriminatory power of microarrays for the direct identification of microorganisms which consume a specific substrate in the environment.

Toxic effects of linear alkylbenzene sulfonate on metabolic activity, growth rate, and microcolony formation of Nitrosomonas and Nitrosospira strains.

Abstract: Strong inhibitory effects of the anionic surfactant linear alkylbenzene sulfonate (LAS) on four strains of autotrophic ammonia-oxidizing bacteria (AOB) are reported. Two Nitrosospira strains were considerably more sensitive to LAS than two Nitrosomonas strains were. Interestingly, the two Nitrosospira strains showed a weak capacity to remove LAS from the medium. This could not be attributed to adsorption or any other known physical or chemical process, suggesting that biodegradation of LAS took place. In each strain, the metabolic activity (50% effective concentration [EC(50)], 6 to 38 mg liter(-1)) was affected much less by LAS than the growth rate and viability (EC(50), 3 to 14 mg liter(-1)) were. However, at LAS levels that inhibited growth, metabolic activity took place only for 1 to 5 days, after which metabolic activity also ceased. The potential for adaptation to LAS exposure was investigated with Nitrosomonas europaea grown at a sublethal LAS level (10 mg liter(-1)); compared to control cells, preexposed cells showed severely affected cell functions (cessation of growth, loss of viability, and reduced NH(4)(+) oxidation activity), demonstrating that long-term incubation at sublethal LAS levels was also detrimental. Our data strongly suggest that AOB are more sensitive to LAS than most heterotrophic bacteria are, and we hypothesize that thermodynamic constraints make AOB more susceptible to surfactant-induced stress than heterotrophic bacteria are. We further suggest that AOB may comprise a sensitive indicator group which can be used to determine the impact of LAS on microbial communities.

Degradation of 4-nonylphenol in homogeneous and nonhomogeneous mixtures of soil and sewage sludge.

Abstract: Sewage sludge is frequently applied as fertilizers to cultivated land However, municipal sewage sludge often contains organic contaminants including nonylphenol (NP), an intermediate from nonionic

Isotope array analysis of Rhodocyclales uncovers functional redundancy and versatility in an activated sludge

Abstract: Extensive physiological analyses of different microbial community members in many samples are difficult because of the restricted number of target populations that can be investigated in reasonable time by standard substrate-mediated isotope-labeling techniques. The diversity and ecophysiology of Rhodocyclales in activated sludge from a full-scale wastewater treatment plant were analyzed following a holistic strategy based on the isotope array approach, which allows for a parallel functional probing of different phylogenetic groups. Initial diagnostic microarray, comparative 16S rRNA gene sequence, and quantitative fluorescence in situ hybridization surveys indicated the presence of a diverse community, consisting of an estimated number of 27 operational taxonomic units that grouped in at least seven main Rhodocyclales lineages. Substrate utilization profiles of probe-defined populations were determined by radioactive isotope array analysis and microautoradiography-fluorescence in situ hybridization of activated sludge samples that were briefly exposed to different substrates under oxic and anoxic, nitrate-reducing conditions. Most detected Rhodocyclales groups were actively involved in nitrogen transformation, but varied in their consumption of propionate, butyrate, or toluene, and thus in their ability to use different carbon sources in activated sludge. This indicates that the functional redundancy of nitrate reduction and the functional versatility of substrate usage are important factors governing niche overlap and differentiation of diverse Rhodocyclales members in this activated sludge.

Isotope Labeling and Microautoradiography of Active Heterotrophic Bacteria on the Basis of Assimilation of 14CO2

Abstract: Most heterotrophic bacteria assimilate CO(2) in various carboxylation reactions during biosynthesis. In this study, assimilation of (14)CO(2) by heterotrophic bacteria was used for isotope labeling of active microorganisms in pure cultures and environmental samples. Labeled cells were visualized by microautoradiography (MAR) combined with fluorescence in situ hybridization (FISH) to obtain simultaneous information about activity and identity. Cultures of Escherichia coli and Pseudomonas putida assimilated sufficient (14)CO(2) during growth on various organic substrates to obtain positive MAR signals. The MAR signals were comparable with the traditional MAR approach based on uptake of (14)C-labeled organic substrates. Experiments with E. coli showed that (14)CO(2) was assimilated during both fermentation and aerobic and anaerobic respiration. The new MAR approach, HetCO(2)-MAR, was evaluated by targeting metabolic active filamentous bacteria, including "Candidatus Microthrix parvicella" in activated sludge. "Ca. Microthrix parvicella" was able to take up oleic acid under anaerobic conditions, as shown by the traditional MAR approach with [(14)C]oleic acid. However, the new HetCO(2)-MAR approach indicated that "Ca. Microthrix parvicella," did not significantly grow on oleic acid under anaerobic conditions with or without addition of NO(2)(-), whereas the addition of O(2) or NO(3)(-) initiated growth, as indicated by detectable (14)CO(2) assimilation. This is a metabolic feature that has not been described previously for filamentous bacteria. Such information could not have been derived by using the traditional MAR procedure, whereas the new HetCO(2)-MAR approach differentiates better between substrate uptake and substrate metabolism that result in growth. The HetCO(2)-MAR results were supported by stable isotope analysis of (13)C-labeled phospholipid fatty acids from activated sludge incubated under aerobic and anaerobic conditions in the presence of (13)CO(2). In conclusion, the novel HetCO(2)-MAR approach expands the possibility for studies of the ecophysiology of uncultivated microorganisms.

Sponge-Associated Microorganisms: Evolution, Ecology, and Biotechnological Potential

Abstract: Marine sponges often contain diverse and abundant microbial communities, including bacteria, archaea, microalgae, and fungi. In some cases, these microbial associates comprise as much as 40% of the sponge volume and can contribute significantly to host metabolism (e.g., via photosynthesis or nitrogen fixation). We review in detail the diversity of microbes associated with sponges, including extensive 16S rRNA-based phylogenetic analyses which support the previously suggested existence of a sponge-specific microbiota. These analyses provide a suitable vantage point from which to consider the potential evolutionary and ecological ramifications of these widespread, sponge-specific microorganisms. Subsequently, we examine the ecology of sponge-microbe associations, including the establishment and maintenance of these sometimes intimate partnerships, the varied nature of the interactions (ranging from mutualism to host-pathogen relationships), and the broad-scale patterns of symbiont distribution. The ecological and evolutionary importance of sponge-microbe associations is mirrored by their enormous biotechnological potential: marine sponges are among the animal kingdom's most prolific producers of bioactive metabolites, and in at least some cases, the compounds are of microbial rather than sponge origin. We review the status of this important field, outlining the various approaches (e.g., cultivation, cell separation, and metagenomics) which have been employed to access the chemical wealth of sponge-microbe associations.

Ammonia-Oxidizing Bacteria: A Model for Molecular Microbial Ecology

Abstract: ▪ Abstract The eutrophication of many ecosystems in recent decades has led to an increased interest in the ecology of nitrogen transformation. Chemolitho-autotrophic ammonia-oxidizing bacteria are responsible for the rate-limiting step of nitrification in a wide variety of environments, making them important in the global cycling of nitrogen. These organisms are unique in their ability to use the conversion of ammonia to nitrite as their sole energy source. Because of the importance of this functional group of bacteria, understanding of their ecology and physiology has become a subject of intense research over recent years. The monophyletic nature of these bacteria in terrestrial environments has facilitated molecular biological approaches in studying their ecology, and progress in this field has been rapid. The ammonia-oxidizing bacteria of the β-subclass Proteobacteria have become somewhat of a model system within molecular microbial ecology, and this chapter reviews recent progress in our knowledge of ...

Removal of endocrine-disrupting chemicals in activated sludge treatment works

Abstract: The release of endocrine-disrupting chemicals into the aquatic environment has raised the awareness of the central role played by sewage treatment in lowland water quality. This review focuses on the activated sludge process, which is commonly used to treat sewage in large towns and cities and which successfully removes the bulk of the organic compounds that enter the works. However, not all compounds are completely broken down or converted to biomass. For example, the estrogenic alkylphenols and steroid estrogens found in effluent are the breakdown products of incomplete breakdown of their respective parent compounds. Batch microcosm studies have indicated that estrone, ethinylestradiol, and alkylphenols will not be completely eliminated in activated sludge over typical treatment times. Field data suggest that the activated sludge treatment process can consistently remove over 85% of estradiol, estriol, and ethinylestradiol. The removal performance for estrone appears to be less and is more variable. Because of its relatively high hydrophobicity, the accumulation of alkylphenol in sludge has been observed. Although it has not been examined, accumulation of ethinylestradiol in sludge is a possibility due to its recalcitrance and hydrophobicity. A comparison between the concentrations of some of the major endocrine-active chemicals in effluents and their biological potencies has been made, to direct attention to the chemicals of most concern. While water purification techniques such as UV or activated charcoal could significantly remove these microorganic contaminants, the high costs involved suggest that research into the potential for treatment optimization should receive more attention.