Search

Combining peatland rewetting with biomass cropping (paludiculture) is one strategy to remove nutrient surpluses from soil/water and stimulate peat-forming vegetation. This approach was tested in the Massaciuccoli Lake Basin (Tuscany, Italy), a coastal floodplain artificially drained for agricultural purposes since 1930, where land reclamation and continuous cropping have contributed to considerable peat degradation and water eutrophication due to nutrient enrichment of surface waters. An experimental trial was established in spring 2012 with three perennial rhizomatous grasses (PRG) (Phragmites australis, Miscanthus × giganteus, Arundo donax) and two woody species managed as short-rotation coppice (SRC) (Salix alba “Dimitrios”, Populus × canadensis “Oudenberg”), aimed to provide biomass for various bioenergy supply chains. A conventionally cultivated annual crop (maize) was the control. The aim of this study was to compare the sustainability of the proposed paludiculture systems to that of conventional annual crops on the basis of yield and nutrient-removal capability. This two-year field study evaluated yields, nutrient concentrations and uptake (N and P) of the crops. Over the two years, A. donax had the highest mean biomass yield (35 Mg ha−1), N uptake (367 kg ha−1), and P uptake (54 kg ha−1). SRCs had the lowest nutrient uptake in both years. Among grasses, the highest N concentration was recorded in A. donax leaves in 2013 (N: 2.41%), while P concentration was greater in S. alba branches (P: 0.39%). The average aboveground biomass of maize was 17.5 Mg ha−1, while the nutrient uptakes were equal to 194 and 27 kg ha−1 for N and P, respectively. Thus, the performances of paludiculture systems were generally encouraging and could represent an important alternative for restoring and managing former drained peatlands in a suitable product chain.

Biological nitrogen (N) fixation is an important process supporting primary production in ecosystems, especially in those where N availability is limiting growth, such as peatlands and boreal forests. In many peatlands, peat mosses (genus Sphagnum) are the prime ecosystem engineers, and like feather mosses in boreal forests, they are associated with a diverse community of diazotrophs (N-2-fixing microorganisms) that live in and on their tissue. The large variation in N-2 fixation rates reported in literature remains, however, to be explained. To assess the potential roles of habitat (including nutrient concentration) and species traits (in particular litter decomposability and photosynthetic capacity) on the variability in N-2 fixation rates, we compared rates associated with various Sphagnum moss species in a bog, the surrounding forest and a fen in Sweden. We found appreciable variation in N-2 fixation rates among moss species and habitats, and showed that both species and habitat conditions strongly influenced N-2 fixation. We here show that higher decomposition rates, as explained by lower levels of decomposition-inhibiting compounds, and higher phosphorous (P) levels, are related with higher diazotrophic activity. Combining our findings with those of other studies, we propose a conceptual model in which both species-specific traits of mosses (as related to the trade-off between rapid photosynthesis and resistance to decomposition) and P availability, explain N-2 fixation rates. This is expected to result in a tight coupling between P and N cycling in peatlands.

Paludiculture, the cultivation of crops on wet or rewetted agricultural peatlands, sustainably integrates productive land use with the provision of multiple ecosystem services. Paludiculture crops thrive under waterlogged conditions that stimulate nitrogen (N) and phosphorus (P) removal from soil and water and convert serious drainage-induced carbon (C) losses to C sequestration. Nutrient uptake by paludicrops can prevent mobilisation after rewetting and provide opportunities for purification of nutrient-rich water. Uncertainty remains, however, if and to what extent N loading and a subsequent increase in biomass productivity affect nutrient cycling as well as emissions of the potent greenhouse gases methane (CH4) and nitrous oxide (N2O). In this study, we use mesocosms with rewetted peat to investigate the effect of different N sources in surface water on biomass production of Typha latifolia, a typical paludiculture crop, and the emissions of CH4 and N2O. Organic (Azolla filiculoides; urea) or mineral (KNO3 ; NH4NO) N was supplied either a single time (steady state) or repeatedly (pulse) to simulate a total surface water load of 150 kg N ha(-1) . We found that N stimulated aboveground and belowground biomass production and nutrient uptake by T. latifolia. These effects were absent in Azolla treatments. Whereas after two months CH4 emissions arose to substantial amounts (> 10 mg CH4 m(-2) day(-1)) in unvegetated mesocosms loaded with organic N, they remained very low (

In pristine Sphagnum-dominated peatlands, (di)nitrogen (N2) fixing (diazotrophic) microbial communities associated with Sphagnum mosses contribute substantially to the total nitrogen input, increasing carbon sequestration. The rates of symbiotic nitrogen fixation reported for Sphagnum peatlands, are, however, highly variable, and experimental work on regulating factors that can mechanistically explain this variation is largely lacking. For two common fen species (Sphagnum palustre and S. squarrosum) from a high nitrogen deposition area (25 kg N ha−1 yr−1), we found that diazotrophic activity (as measured by 15 − 15N2 labeling) was still present at a rate of 40 nmol N gDW−1 h−1. This was surprising, given that nitrogen fixation is a costly process. We tested the effects of phosphorus availability and buffering capacity by bicarbonate-rich water, mimicking a field situation in fens with stronger groundwater or surface water influence, as potential regulators of nitrogen fixation rates and Sphagnum performance. We expected that the addition of phosphorus, being a limiting nutrient, would stimulate both diazotrophic activity and Sphagnum growth. We indeed found that nitrogen fixation rates were doubled. Plant performance, in contrast, did not increase. Raised bicarbonate levels also enhanced nitrogen fixation, but had a strong negative impact on Sphagnum performance. These results explain the higher nitrogen fixation rates reported for minerotrophic and more nutrient-rich peatlands. In addition, nitrogen fixation was found to strongly depend on light, with rates 10 times higher in light conditions suggesting high reliance on phototrophic organisms for carbon. The contrasting effects of phosphorus and bicarbonate on Sphagnum spp. and their diazotrophic communities reveal strong differences in the optimal niche for both partners with respect to conditions and resources. This suggests a trade-off for the symbiosis of nitrogen fixing microorganisms with their Sphagnum hosts, in which a sheltered environment apparently outweighs the less favorable environmental conditions. We conclude that microbial activity is still nitrogen limited under eutrophic conditions because dissolved nitrogen is being monopolized by Sphagnum. Moreover, the fact that diazotrophic activity can significantly be upregulated by increased phosphorus addition and acid buffering, while Sphagnum spp. do not benefit, reveals remarkable differences in optimal conditions for both symbiotic partners and calls into question the regulation of nitrogen fixation by Sphagnum under these eutrophic conditions. The high nitrogen fixation rates result in high additional nitrogen loading of 6 kg ha−1 yr−1 on top of the high nitrogen deposition in these ecosystems.

Mires and peatlands in general are heavily influenced by anthropogenicstressors like acidification, eutrophication, desiccation and fragmentation.Groundwater-fed mires are, in contrast to rainwater-fed mires, often wellprotected against desiccation due to constant groundwater discharge.Groundwater-fed mires can however be influenced by groundwater pollutionsuch as groundwater nitrate enrichment, a threat which has received minorattention in literature. The present case study demonstrates how groundwaternitrate enrichment can affect the biogeochemical functioning and vegetationcomposition of groundwater-fed mires through direct nitrogen enrichment andindirect nitrate-induced sulphate mobilisation from geological deposits.Biogeochemical and ecohydrological analyses suggest that the Dutchgroundwater-fed mire studied is influenced by different water sources(rainwater; groundwater of local and regional origin) with differing chemicalcompositions. The weakly buffered and nitrate-enriched groundwater leads,where it reaches the uppermost peat, to nitrogen enrichment, enhanced isotopicnitrogen signatures and altered the vegetation composition at the expense ofcharacteristic species. Nitrate-induced sulphate mobilisation in the aquifer ledto enhanced sulphate reduction, sulphide toxicity and elemental sulphurdeposition in the mire. Despite sulphate reduction and nitrate enrichment,internal eutrophication did not play an important role, due to relatively lowphosphorus concentrations and/or low iron-bound phosphorus of the peat soil.Future management of groundwater-fed mires in nitrate-polluted aquifersshould include the reduction of nitrate leaching to the aquifer at the rechargeareas by management and ecohydrological restoration measures on both a localand landscape scale.

The agricultural use of drained peatlands leads to huge emissions of greenhouse gases and nutrients. A land-use alternative that allows rewetting of drained peatland while maintaining agricultural production is the cultivation of Sphagnum biomass as a renewable substitute for fossil peat in horticultural growing media (Sphagnum farming). We studied Sphagnum productivity and nutrient dynamics during two years in two Sphagnum farming sites in NW Germany, which were established on drained bog grassland by sod removal, rewetting, and the introduction of Sphagnum fragments in 2011 and 2016, respectively. We found a considerable and homogeneous production of Sphagnum biomass (>3.6 ton DW ha- −1 yr−1), attributable to the high nutrient levels, low alkalinity, and even distribution of the irrigation water. The ammonium legacy from former drainage-based agriculture rapidly declined after rewetting, while nutrient mobilization was negligible. CH4 concentrations in the rewetted soil quickly decreased to very low levels. The Sphagnum biomass sequestered high loads of nutrients (46.0 and 47.4 kg N, 3.9 and 4.9 kg P, and 9.8 and 16.1 kg K ha− 1 yr− 1 in the 7.5 y and 2.5 y old sites, respectively), preventing off-site eutrophication. We conclude that Sphagnum farming as an alternative for drainage-based peatland agriculture may contribute effectively to tackling environmental challenges such as local and regional downstream pollution and global climate change.

Pristine bogs, peatlands in which vegetation is exclusively fed by rainwater (ombrotrophic), typically have a low atmospheric deposition of reactive nitrogen (N) (Here, we studied the effects of 11 years of experimentally increased deposition (32 versus 8 kg N ha(-1) y(-1)) of either NH4+ or NO3- on N accumulation in three moss and one lichen species (Sphagnum capillifolium, S. papillosum, Pleurozium schreberi and Cladonia portentosa), N-2 fixation rates of their symbionts, and potential N losses to peat soil and atmosphere, in a bog in Scotland.Increased input of both N forms led to 15-90% increase in N content for all moss species, without affecting their cover. The keystone species S. capillifolium showed 4 times higher N allocation into free amino acids, indicating N stress, but only in response to increased NH4+. In contrast, NO3- addition resulted in enhanced peat N mineralization linked to microbial NO(3)(-)reduction, increasing soil pH, N concentrations and N losses via denitrification. Unexpectedly, increased deposition from 8 to 32 kg ha(-1) y(-1) in both N forms did not affect N-2 fixation rates for any of the moss species and corresponded to an additional input of 5 kg N ha(-1) y(-1) with a 100% S. capillifolium cover. Since both N forms clearly show differential effects on living Sphagnum and biogeochemical processes in the underlying peat, N form should be included in the assessment of the effects of N pollution on peatlands. (C) 2017 Elsevier B.V. All rights reserved.

Research rationale Groundwater-fed fens are known sources of methane (CH4) emissions to the atmosphere, but these are known to be mediated by vegetation. In a fen located in the Bale Mountains, Ethiopia, we assessed the effects of a cushion plant (Eriocaulon schimperi) and a sedge species (Carex monostachya) on rhizosphere biogeochemistry. Central methods CH4 and CO2 concentrations and pH were measured in pore water at different depths in the profile. Redox potentials and NaCl-extractable element concentrations were analyzed in soil samples from sites dominated by either E. schimperii or C. monostachya. Nutrient and elemental concentration were analyzed in plant tissuesl. Key results At Carex-dominated sites, CH4 concentrations increased from 70 μmol l−1 at a depth of 10cm to 130 μmol l−1 at a depth of 100 cm. CH4 concentrations at Eriocaulon-dominated sites were almost zero (< 1 μmol l−1), up to a depth of 100cm. Simultaneously, soil redox potentials and CO2 concentrations were higher at Eriocaulon-dominated sites, indicating a low potential for CH4 production and a high potential for CH4 oxidation. Main conclusions E. schimperi displayed a root-investment strategy to cope with the harsh environment, similarly to the cushion plant Astelia pumila in Patagonian bogs. This strategy is characterized by high root/shoot ratios, high root porosity and density, under high redox conditions. Both cushion plant species create an aerobic rhizosphere by radial oxygen loss from deep roots, which strongly reduce CH4 fluxes to the atmosphere. This article is protected by copyright. All rights reserved.

Large areas of peatlands have worldwide been drained to facilitate agriculture, which has adverse effects on the environment and the global climate. Agriculture on rewetted peatlands (paludiculture) provides a sustainable alternative to drainage-based agriculture. One form of paludiculture is the cultivation of Sphagnum moss, which can be used as a raw material for horticultural growing media. Under natural conditions, most Sphagnum mosses eligible for paludiculture typically predominate only in nutrient-poor wetland habitats. It is unknown, however, how the prevailing high nutrient levels in rewetted agricultural peatlands interfere with optimal Sphagnum production.We therefore studied the effect of enriched nutrient conditions remaining even after top soil removal and further caused by external supply of nutrient-rich irrigation water and (generally) high inputs of atmospheric nitrogen (N) to habitat biogeochemistry, biomass production and nutrient stoichiometry of introduced Sphagnum palustre and S. papillosum in a rewetted peatland, which was formerly in intensive agricultural use.Airborne N was responsible for the major supply of N. Phosphorus (P) and potassium (K) were mainly supplied by irrigation water. The prevailing high nutrient levels (P and K) are a result of nutrient-rich irrigation water from the surroundings. Peat porewater (10 cm below peatmoss surface) CO2 concentrations were high, bicarbonate concentrations low, and the pH was around 4.2.Provided that moisture supply is sufficient and dominance of fast-growing, larger graminoids suppressed (in order to avoid outshading of Sphagnum mosses), strikingly very high biomass yields of 6.7 and 6.5 t DW ha(-1) yr(-1) (S, palustre and S. papillosum [including S. fallax biomass], respectively) were obtained despite high N supply and biomass N concentrations. Despite high P and K supply and uptake, N:P and N:K ratios in the Sphagnum capitula were still low. Sphagnum mosses achieved high nutrient sequestration rates of 34 kg N, 17 kg K and 4 kg P ha(-1) yr(-1) from May 2013 to May 2014, which shows that the site acted as an active nutrient sink. Nutrient management still needs further improvement to reduce the competitive advantage of fast growing peatmoss species (cf. S. fallax) at the expense of slower growing but preferred peatmosses as horticultural substrate (S. palustre and S. papillosum) to optimize the quality of biomass yields.In conclusion, Sphagnum farming is well able to thrive under high N input provided that there is a simultaneous high input of P and K from irrigation water, which facilitates high production rates. Due to the lack of suitable, nutrient poor sites, it seems to be useful to remove the topsoil (mainly P removal) prior to start growing Sphagnum mosses. In addition, bicarbonate concentrations have to stay sufficientlylow to ensure a low pH, CO2 supply from the peat soil should be sufficiently high to prevent C limitation, and graminoids should be mown regularly. (C) 2016 Elsevier B.V. All rights reserved.

En el Hemisferio Sur las turberas almacenan grandes cantidades de carbono en el suelo. A pesar de su importancia en el ciclo global del carbono, se sabe poco acerca de los procesos de descomposición y su diversidad fúngica. El presente estudio se realizó para describir la composición de hongos filamentosos en dos profundidades de una turbera compacta donde las especies vegetales predominantes son Astelia (Asteliaceae) y Donatia (Donatiaceae) en Moat, Tierra del Fuego, Argentina. De 48 muestras procesadas, se obtuvieron 338 aislamientos. Mediante el uso de diferentes metodologías de cultivo, a través de observación microscópica y por métodos moleculares identificamos 38 especies fúngicas y 18 géneros de Ascomycetes y Zygomycetes. Los aislamientos de Ascomycetes fueron los más abundantes, con dominancia de Penicillium y Trichoderma. Se describe la composición fúngica y se comparó la diversidad y equitatividad de las especies a dos profundidades de muestreo. No se encontraron diferencias significativas entre la composición de especies, la diversidad y equitatividad. La turbera estudiada es un ecosistema que presenta alta diversidad de especies fúngicas filamentosas, algunas de ellas descritas en otras turberas en todo el mundo. Southern Hemisphere peatlands store substantial amounts of soil carbon. Despite their importance in the global carbon cycle, little is known about decomposition processes and the associated fungal diversity. The present study describes the composition of fungal assemblage in two depths from a cushion peatland of predominating Astelia (Asteliaceae) and Donatia (Donatiaceae) species in Moat, Tierra del Fuego. From 48 samples processed, we obtained 338 isolates. Using different culturing methodologies, through direct and microscopic observation and using molecular methods we identified 38 fungal species and 18 genera of Ascomycetes and Zygomycetes. Isolates belonging to Ascomycetes were the most abundant, with dominance of Penicillium and Trichoderma. We described fungal composition and compared species diversity and evenness across two dephts. No differences in the diversity index and evenness were found between depths. The studied peat is an ecosystem that has a great diversity of filamentous fungal species, some of which are described in other peatlands worldwide. Instituto de Botánica "Dr. Carlos Spegazzini"

In pristine ombrotrophic Sphagnum-dominated peatland ecosystems nitrogen (N) is often a limiting nutrient, which is replenished by biological N-2 fixation and atmospheric N deposition. It is, however, unclear which impact long-term N deposition has on microbial N-2 fixing activity and diazotrophic diversity, and whether phosphorus (P) modulates the response. Therefore, we studied the impact of increased N deposition and N depletion on microbial N-2 fixation and diazotrophic diversity associated with the peat moss Sphagnum magellanicum, and their interaction with P availability.Nitrogenase activities of S. magellanicum-associated microorganisms were determined by acetylene reduction assays (ARA) and N-15(2) tracer methods on mosses from two geographically distinct locations with different N deposition histories, high or low N deposition, and in samples depleted in N (grown 3 years in the greenhouse) versus recent field samples. The short-term response to increased N deposition was tested for mosses differing in N and P fertilization histories. In addition, diversity of diazotrophic microorganisms was assessed by nifH gene amplicon sequencing of N-depleted mosses.We showed distinct and persistent differences in diazotrophic communities and their activities associated with S. magellanicum from sites with high versus low N deposition. Initially, diazotrophic activity was six times higher for the low N site. During incubation and repeated ARA, however, this activity strongly decreased, while it remained stable for the high N site. Activity for the high N site could not be increased by long-term experimental N deprivation. Short-term, experimental N application had an inhibitory effect on N-2 fixation for both sites, which was not observed in mosses with high indirect P availability.We conclude that although N deposition negatively affects N-2 fixation as also shown in previous studies, long-term effects of N deprivation on the diazotrophic activity and community are more complex. Furthermore, our results indicated that P availability might be an important factor in modulating the response of Sphagnum-associated diazotrophs to N deposition.

Sphagnum peatlands are important ecosystems in the methane cycle. Methanotrophs living inside the dead hyaline cells or on the Sphagnum mosses are able to act as a methane filter and thereby reduce methane emissions. We investigated in situ methane concentrations and the corresponding activity and diversity of methanotrophs in different Sphagnum dominated bog microhabitats. In contrast to the Northern Hemisphere peat ecosystems the temperate South American peat bogs are dominated by one moss species; Sphagnum magellanicum. This permitted a species-independent comparison of the different bog microhabitats. Potential methane oxidizing activity was found in all Sphagnum mosses sampled and a positive correlation was found between activity and in situ methane concentrations. Substantial methane oxidation activity (23 μmol CH4 gDW−1 day−1) was found in pool mosses and could be correlated with higher in situ methane concentrations (>35 μmol CH4 l−1 pore water). Little methanotrophic activity (4 μmol CH4 gDW−1 day−1) in Sphagnum litter at depths around the water levels and rich in methane. The total bacterial community was studied using 16S rRNA gene sequencing and the methanotrophic communities were studied using a pmoA microarray and a complementary pmoA clone library. The methanotrophic diversity was similar in the different habitats of this study and comparable to the methanotrophic diversity found in peat mosses from the Northern Hemisphere. The pmoA microarray data indicated that both alpha- and gammaproteobacterial methanotrophs were present in all Sphagnum mosses, even in those mosses with a low initial methane oxidation activity. Prolonged incubation of Sphagnum mosses from lawn and hummock with methane revealed that the methanotrophic community present was viable and showed an increased activity within 15 days. The high abundance of methanotrophic Methylocystis species in the most active mosses suggests that these might be responsible for the bulk of methane oxidation.

Sphagnum-bog ecosystems have a limited capability to retain carbon and nutrients when subjected to increased nitrogen (N) deposition. Although it has been proposed that phosphorus (P) can dilute negative effects of nitrogen by increasing biomass production of Sphagnum mosses, it is still unclear whether P-addition can alleviate physiological N-stress in Sphagnum plants. A 3-year fertilisation experiment was conducted in lawns of a pristine Sphagnum magellanicum bog in Patagonia, where competing vascular plants were practically absent. Background wet deposition of nitrogen was low (≈ 0.1-0.2 g · N · m(-2) · year(-1)). Nitrogen (4 g · N · m(-2) · year(-1)) and phosphorus (1 g · P · m(-2) · year(-1)) were applied, separately and in combination, six times during the growing season. P-addition substantially increased biomass production of Sphagnum. Nitrogen and phosphorus changed the morphology of Sphagnum mosses by enhancing height increment, but lowering moss stem density. In contrast to expectations, phosphorus failed to alleviate physiological stress imposed by excess nitrogen (e.g. amino acid accumulation, N-saturation and decline in photosynthetic rates). We conclude that despite improving growth conditions by P-addition, Sphagnum-bog ecosystems remain highly susceptible to nitrogen additions. Increased susceptibility to desiccation by nutrients may even worsen the negative effects of excess nitrogen especially in windy climates like in Patagonia.

Peat forming Sphagnum mosses are able to prevent the dominance of vascular plants under ombrotrophic conditions by efficiently scavenging atmospherically deposited nitrogen (N). N-uptake kinetics of these mosses are therefore expected to play a key role in differential N availability, plant competition, and carbon sequestration in Sphagnum peatlands. The interacting effects of rain N concentration and exposure time on moss N-uptake rates are, however, poorlyunderstood. We investigated the effects of N-concentration (1, 5, 10, 50, 100, 500 mM), N-form (15N - ammonium or nitrate) and exposure time (0.5, 2, 72 h) on uptake kinetics for Sphagnum magellanicum from a pristine bog in Patagonia(Argentina) and from a Dutch bog exposed to decades of N-pollution. Uptake rates for ammonium were higher than for nitrate, and N-binding at adsorption sites was negligible. During the first 0.5 h, N-uptake followed saturation kineticsrevealing a high affinity (Km 3.5–6.5 mM). Ammonium was taken up 8 times faster than nitrate, whereas over 72 hours this was only 2 times. Uptake rates decreased drastically with increasing exposure times, which implies that many short-term Nuptake experiments in literature may well have overestimated long-term uptake rates and ecosystem retention. Sphagnum from the polluted site (i.e. long-term N exposure) showed lower uptake rates than mosses from the pristine site, indicating an adaptive response. Sphagnum therefore appears to be highly efficient in using short N pulses (e.g. rainfall in pristine areas). This strategy has important ecological and evolutionary implications: at high N input rates, the risk of N-toxicity seems to be reduced by lower uptake rates of Sphagnum, at the expense of its long-term filter capacity and relatedcompetitive advantage over vascular plants. As shown by our conceptual model, interacting effects of N-deposition and climate change (changes in rainfall) will seriously alter the functioning of Sphagnum peatlands.

Mycobacterium tuberculosis and Mycobacterium bovis cause tuberculosis, which is responsible for the deaths of more people each year than any other bacterial infectious disease. Disseminated disease with Mycobacterium bovis BCG, the only currently available vaccine against tuberculosis, occurs in immunocompetent and immunodeficient individuals. Although mycobacteria are obligate aerobes, they are thought to face an anaerobic environment during infection, notably inside abscesses and granulomas. The purpose of this study was to define a metabolic pathway that could allow mycobacteria to exist under these conditions. Recently, the complete genome of M. tuberculosis has been sequenced, and genes homologous to an anaerobic nitrate reductase (narGHJI), an enzyme allowing nitrate respiration when oxygen is absent, were found. Here, we show that the narGHJI cluster of M. tuberculosis is functional as it conferred anaerobic nitrate reductase activity to Mycobacterium smegmatis. A narG mutant of M. bovis BCG was generated by targeted gene deletion. The mutant lacked the ability to reduce nitrate under anaerobic conditions. Both mutant and M. bovis BCG wild type grew equally well under aerobic conditions in vitro. Histology of immunodeficient mice (SCID) infected with M. bovis BCG wild type revealed large granulomas teeming with acid-fast bacilli; all mice showed signs of clinical disease after 50 days and succumbed after 80 days. In contrast, mice infected with the mutant had smaller granulomas containing fewer bacteria; these mice showed no signs of clinical disease after more than 200 days. Thus, it seems that nitrate respiration contributes significantly to virulence of M. bovis BCG in immunodeficient SCID mice.

Mycobacterium bovis BCG, the only presently available vaccine against tuberculosis, was obtained from virulent M. bovis after serial passages in vitro. The vaccine strain retained at least some of its original virulence, as it persists in immune-competent hosts and occasionally may cause fatal disease in immune-deficient hosts. Mycobacterial persistence in vivo is thought to depend on anaerobic metabolism, an apparent paradox since all mycobacteria are obligate aerobes. Here we report that M. bovis BCG lacking anaerobic nitrate reductase (NarGHJI), an enzyme essential for nitrate respiration, failed to persist in the lungs, liver, and kidneys of immune-competent (BALB/c) mice. In immune-deficient (SCID) mice, however, bacilli caused chronic infection despite disruption of narG , even if growth of the mutant was severely impaired in lungs, liver, and kidneys. Persistence and growth of BCG in the spleens of either mouse strain appeared largely unaffected by lack of anaerobic nitrate reductase, indicating that the role of the enzyme in pathogenesis is tissue specific. These data suggest first that anaerobic nitrate reduction is essential for metabolism of M. bovis BCG in immune-competent but not immune-deficient mice and second that its role in mycobacterial disease is tissue specific, both of which are observations with important implications for pathogenesis of mycobacteria and vaccine development.