Nutrient-poor Environments Research Articles

Microbial Diversity in Phosphate Rock and Phosphogypsum

Phosphate rock (PR) and phosphogypsum (PG) contain heavy metals, radionuclides and are exposed to ultraviolet and cycles of desiccation (i.e., Gafsa and Sfax in Tunisia). Nevertheless, an extensive diversity of bacterial species has been identified in such extreme and nutrient-poor environments. This mini-review aims to summarize findings published so far about microbes isolated, enriched from or able to grow on PR and PG. Concerning the ecology of these two complex environments, this survey has underscored the importance of key microbial genera or consortia associated with at least one of these phenotypes: (1) phosphate solubilization, (2) heavy metals tolerance, (3) radiation resistance—positively correlated to desiccation tolerance, (4) sulfur oxidation—associated to polyphosphate stocking and (5) sulfate (SO4 2−) reduction.

Abstract B112: Targeting immunotherapy to the tumor microenvironment using anti-PDL1 VHH

Abstract Cytokines and other immune modulating agents act locally, and delivery of particular immune based therapies to the right cell population in the tumor has been challenging. Many agents have systemic toxicities. Many others fail to arrive in the tumor, and delivering multiple agents to tumor infiltrating lymphocytes is likewise problematic. Pancreatic cancer is the best example of a stroma-rich tumor, where drug delivery often fails. Immunotherapy has shown impressive clinical benefit for many malignancies, particularly for metastatic melanoma; however, pancreatic cancer is among the few cancer types in which anti-CTLA-4 and PD-1 blockade have largely failed. PDAC is fairly average in terms of mutational burden, PDL1 expression, and T cell infiltration, thus the failure to respond to immune checkpoint blockade cannot be explained by these factors. PDAC is uniquely distinguished by a dense stromal reaction, resulting in a nutrient-poor immunosuppressive environment. We hypothesize that targeted delivery of a combination of immunomodulatory agents will change the pancreatic tumor microenvironment to relieve immunosuppression will allow for more effective anti-tumor immune responses. Alpacas and other camelid species generate single domain antibodies, the variable portions of which can be expressed recombinantly and retain the binding properties of full-size antibodies at 1/10th the size. We have generated high-affinity VHHs specific for mouse and human PD-L1. We show by immuno-positron emission tomography (PET) that small VHHs penetrate deeply into orthotopic pancreatic tumors, and can effectively deliver payloads to the tumor interior. Pancreatic tumor cells, whether growing in culture or growing in an orthotopic tumor, express high levels of PD-L1 at baseline. PD-L1 is largely absent from normal tissues; thus we can use PDL1-VHH as a tumor-specific targeting agent. PDL1-VHH was conjugated to the cytokines IL-2 or IFNγ, and we looked for an effect of these reagents in both melanoma and an orthotopic model of pancreatic cancer. Both reagents reduce the growth of B16 tumors in conjunction with an antibody against the melanoma protein TRP1 (TA99). For pancreatic cancer, aPDL1-IL2 treatment showed a 50% reduction in overall tumor burden, an increase in the intratumoral ratio of CD8+ T cells to CD4+Tregs, and increased T cell trafficking to the tumor microenvironment. aPDL1-IFNγ caused a profound reduction in size of both Panc02 and KPC orthotopic tumors, largely by reprogramming intratumoral macrophages. Here we exploit the near-ubiquitous expression of PD-L1 by tumors to focus immune therapies on the tumor microenvironment, and propose that this may be a general technique for enhancing responses to immune therapy, while greatly reducing the risk of systemic toxicities. Citation Format: Michael Dougan, Jessica Ingram, Hidde Ploegh, Stephanie K. Dougan. Targeting immunotherapy to the tumor microenvironment using anti-PDL1 VHH [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr B112.

Eutrophication alters Si cycling and litter decomposition in wetlands

Anthropogenic eutrophication of wetlands may have a significant impact on the global biogeochemical silicon (Si) cycle, as Si filtering by wetland vegetation codetermines fluxes of Si towards the oceans. We experimentally investigated how macronutrient (NPK) enrichment alters total Si storage and Si stoichiometry in litter from six wetland species of Carex, which we related to other parameters of litter quality and litter decomposition rates. Nutrient enrichment stimulated primary biomass production, which resulted in an increased total Si storage in plants. However, this eutrophication-induced stimulatory effect on Si fixation in plant biomass was counterbalanced by consistently lower (up to 50 % reduction) litter Si concentrations in all species, suggesting a plant-physiological response following the relief of nutrient stress. Moreover, competitive species (typical for eutrophic conditions) tended to accumulate less Si (per g DM) than slow-growing species (typical for nutrient-poor conditions). Finally, a negative correlation between litter Si concentrations and litter decomposition rates in nutrient-poor environments suggested an inhibiting effect of Si on decomposition. However, negative correlations between litter Si concentrations and litter macronutrient concentrations as well as positive correlations between litter Si concentrations and C:N and lignin:N ratios indicated a strong interdependence of Si with other litter quality parameters that determine decomposition. We conclude that stimulatory effects of eutrophication on total Si storage in wetland vegetation (following an increase in biomass production) need to be balanced with the plant-physiological response of lower tissue Si concentrations. We argue that rates of Si cycling are likely to be altered through shifts in litter quality and decomposition rates.

Eutrophication triggers contrasting multilevel feedbacks on litter accumulation and decomposition in fens.

Eutrophication is a major threat for the persistence of nutrient-poor fens, as multilevel feedbacks on decomposition rates could trigger carbon loss and increase nutrient cycling. Here, we experimentally investigate the effects of macronutrient (NPK) enrichment on litter quality of six species of sedge (Carex sp.), which we relate to litter decomposition rates in a nutrient-poor and nutrient-rich environment. Our research focused on four levels: we examined how eutrophication alters (1) fresh litter production ("productivity shift"), (2) litter stoichiometry within the same species ("intraspecific shift"), (3) overall litter stoichiometry of the vegetation under the prediction that low-competitive species are outcompeted by fast-growing competitors ("interspecific shift"), and (4) litter decomposition rates due to an altered external environment (e.g., shifts in microbial activity; "exogenous shift"). Eutrophication triggered a strong increase in fresh litter production. Moreover, individuals of the same species produced litter with lower C:N and C:P ratios, higher K contents, and lower lignin, Ca and Mg contents (intraspecific shift), which increased litter decomposability. In addition, species typical for eutrophic conditions produced more easily degradable litter than did species typical for nutrient-poor conditions (interspecific shift). However, the effects of nutrient loading of the external environment (exogenous shift) were contradictory. Here, interactions between litter type and ambient nutrient level indicate that the (exogenous) effects of eutrophication on litterdecomposition rates are strongly dependent of litter quality. Moreover, parameters of litter quality only correlated with decomposition rates for litter incubated in nutrient-poor environments, but not in eutrophic environments. This suggests that rates of litter decomposition can be uncoupled from litter stoichiometry under eutrophic conditions. In conclusion, our results show that eutrophication affects litter accumulation and -decomposition at multiple levels, in which stimulatory and inhibitory effects interact. The cumulative effect of these interactions ultimately determine whether peatlands remain sinks or become sources of carbon under eutrophic conditions.

Trade-off between soluble protein production and nutritional storage in Bromeliaceae.

Bromeliads are able to occupy some of the most nutrient-poor environments especially because they possess absorptive leaf trichomes, leaves organized in rosettes, distinct photosynthetic pathways [C3, Crassulacean acid metabolism (CAM) or facultative C3-CAM], and may present an epiphytic habit. The more derived features related to these traits are described for the Tillandsioideae subfamily. In this context, the aims of this study were to evaluate how terrestrial predators contribute to the nutrition and performance of bromeliad species, subfamilies and ecophysiological types, whether these species differ in their ecophysiological traits and whether the physiological outcomes are consistent among subfamilies and types (e.g. presence/absence of tank, soil/tank/atmosphere source of nutrients, trichomes/roots access to nutrients). Isotopic (15N-enriched predator faeces) and physiological methods (analyses of plant protein, amino acids, growth, leaf mass per area and total N incorporated) in greenhouse experiments were used to investigate the ecophysiological contrasts between Tillandsioideae and Bromelioideae, and among ecophysiological types when a predatory anuran contributes to their nutrition. It was observed that Bromelioideae had higher concentrations of soluble protein and only one species grew more (Ananas bracteatus), while Tillandsioideae showed higher concentrations of total amino acids, asparagine and did not grow. The ecophysiological types that showed similar protein contents also had similar growth. Additionally, an ordination analysis showed that the subfamilies and ecophysiological types were discrepant considering the results of the total nitrogen incorporated from predators, soluble protein and asparagine concentrations, relative growth rate and leaf mass per area. Bromeliad subfamilies showed a trade-off between two strategies: Tillandsioideae stored nitrogen into amino acids possibly for transamination reactions during nutritional stress and did not grow, whereas Bromelioideae used nitrogen for soluble protein production for immediate utilization, possibly for fast growth. These results highlight that Bromeliaceae evolution may be directly associated with the ability to stock nutrients.

Pancreatic stellate cells support tumour metabolism through autophagic alanine secretion.

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive disease characterized by an intense fibrotic stromal response and deregulated metabolism. The role of the stroma in PDAC biology is complex and it has been shown to play critical roles that differ depending on the biological context. The stromal reaction also impairs the vasculature, leading to a highly hypoxic, nutrient-poor environment. As such, these tumours must alter how they capture and use nutrients to support their metabolic needs. Here we show that stroma-associated pancreatic stellate cells (PSCs) are critical for PDAC metabolism through the secretion of non-essential amino acids (NEAA). Specifically, we uncover a previously undescribed role for alanine, which outcompetes glucose and glutamine-derived carbon in PDAC to fuel the tricarboxylic acid (TCA) cycle, and thus NEAA and lipid biosynthesis. This shift in fuel source decreases the tumour’s dependence on glucose and serum-derived nutrients, which are limited in the pancreatic tumour microenvironment. Moreover, we demonstrate that alanine secretion by PSCs is dependent on PSC autophagy, a process that is stimulated by cancer cells. Thus, our results demonstrate a novel metabolic interaction between PSCs and cancer cells, in which PSC-derived alanine acts as an alternative carbon source. This finding highlights a previously unappreciated metabolic network within pancreatic tumours in which diverse fuel sources are used to promote growth in an austere tumour microenvironment.

Genomic characterization of symbiotic mycoplasmas from the stomach of deep-sea isopod bathynomus sp.

Deep-sea isopod scavengers such as Bathynomus sp. are able to live in nutrient-poor environments, which is likely attributable to the presence of symbiotic microbes in their stomach. In this study we recovered two draft genomes of mycoplasmas, Bg1 and Bg2, from the metagenomes of the stomach contents and stomach sac of a Bathynomus sp. sample from the South China Sea (depth of 898 m). Phylogenetic trees revealed a considerable genetic distance to other mycoplasma species for Bg1 and Bg2. Compared with terrestrial symbiotic mycoplasmas, the Bg1 and Bg2 genomes were enriched with genes encoding phosphoenolpyruvate-dependent phosphotransferase systems (PTSs) and sodium-driven symporters responsible for the uptake of sugars, amino acids and other carbohydrates. The genome of mycoplasma Bg1 contained sialic acid lyase and transporter genes, potentially enabling the bacteria to attach to the stomach sac and obtain organic carbons from various cell walls. Both of the mycoplasma genomes contained multiple copies of genes related to proteolysis and oligosaccharide degradation, which may help the host survive in low-nutrient conditions. The discovery of the different types of mycoplasma bacteria in the stomach of this deep-sea isopod affords insights into symbiotic model of deep-sea animals and genomic plasticity of mycoplasma bacteria.

Environmental metabarcoding reveals contrasting microbial communities at two poplar phytomanagement sites

The aim of the present study is to deepen the current understanding of the microbial communities at two poplar phytomanagement sites to reveal the environmental factors that drive the abundance, diversity and composition of microbial communities. A soil analysis revealed that the two soils displayed contrasting physico-chemical characteristics, with significant lower pH and higher Cd, Zn and Mn CaCl2-extractable fractions at Leforest site, compared with Pierrelaye site. The fungal and bacterial community profiles in the poplar roots and soils were assessed through Illumina MiSeq sequencing. Diversity indices and β-diversity measures illustrated that the root microbial communities were well separated from the soil microbial communities at both sites. A detailed study of the fungal composition showed that Ascomycota dominated the overall fungal communities on poplar soil, the root samples at Pierrelaye, and the unplanted soil at the experimental sites. Conversely, Basidiomycota accounted for a much higher percentage of the fungal community in poplar root samples from the Leforest site. The root bacterial communities were dominated by Alphaproteobacteria and Actinobacteria, and the soil samples were dominated by Alphaproteobacteria and Acidobacteria. The occurrence and dominance of the ectomycorrhizal community at Leforest but not at Pierrelaye is the major feature of our data set. Overall, ectomycorrhizal root symbionts appeared to be highly constrained by soil characteristics at the phytomanagement sites. Our data support the view that mycorrhizal inoculation is needed in highly stressed and nutrient-poor environments.

Abstract PL02-01: Isogenic tumors can utilize heterogeneous mechanisms of nutrient uptake

Abstract An emerging feature of cancer cell metabolism is the ability to acquire the anabolic precursors necessary to support cell viability and growth from a nutrient-poor environment. Cell proliferation studies undertaken under nutrient-limiting conditions have led us to define two distinct pathways by which tumor cells gain a competitive advantage over their nontransformed counterparts. One pathway is defined by enhanced capture of existing glucose and amino acids through nutrient-selective transporters. The key mediators of this pathway are AKT and its downstream effector, mTORC1. The other pathway depends on the uptake and degradation of extracellular proteins and lipids. Oncogenic forms of RAS are potent activators of this pathway. Many tumors appear capable of using both nutrient uptake pathways and can switch between them depending on extracellular nutrient conditions. Implications of these findings for tumor heterogeneity and therapeutic responsiveness will be discussed. Citation Format: Craig B. Thompson, Wilhelm Palm, Jiangbin Ye, Natalya N. Pavlova, Bryan King. Isogenic tumors can utilize heterogeneous mechanisms of nutrient uptake. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr PL02-01.

Plant invasion is associated with higher plant-soil nutrient concentrations in nutrient-poor environments.

Plant invasion is an emerging driver of global change worldwide. We aimed to disentangle its impacts on plant-soil nutrient concentrations. We conducted a meta-analysis of 215 peer-reviewed articles and 1233 observations. Invasive plant species had globally higher N and P concentrations in photosynthetic tissues but not in foliar litter, in comparison with their native competitors. Invasive plants were also associated with higher soil C and N stocks and N, P, and K availabilities. The differences in N and P concentrations in photosynthetic tissues and in soil total C and N, soil N, P, and K availabilities between invasive and native species decreased when the environment was richer in nutrient resources. The results thus suggested higher nutrient resorption efficiencies in invasive than in native species in nutrient-poor environments. There were differences in soil total N concentrations but not in total P concentrations, indicating that the differences associated to invasive plants were related with biological processes, not with geochemical processes. The results suggest that invasiveness is not only a driver of changes in ecosystem species composition but that it is also associated with significant changes in plant-soil elemental composition and stoichiometry.

Strong linkage between plant and soil fungal communities along a successional coastal dune system.

Complex interactions between plants and soil microorganisms drive key ecosystem and community properties such as productivity and diversity. In nutrient-poor systems such as sand dunes, plant traits and fungal symbioses related to nutrient acquisition can strongly influence vegetation dynamics. We investigated plant and fungal communities in a relic foredune plain located on an archipelago in Québec, Canada. We detected distinct communities across the edaphic and successional gradient. Our results showed a clear increase in plant species richness, as well as in the diversity of nutrient-acquisition strategies. We also found a strong correlation between aboveground vegetation and soil fungal communities, and both responded similarly to soil physicochemical properties. Soil pH influenced the composition of plant and fungal communities, and could act as an important environmental filter along this relic foredune plain. The increasing functional diversity in plant nutrient-acquisition strategies across the gradient might favor resource partitioning and facilitation among co-occurring plant species. The coordinated changes in soil microbial and plant communities highlight the importance of aboveground-belowground linkages and positive biotic interactions during ecological succession in nutrient-poor environments.

Raptor hunted by caspases.

Emergence of survival strategies is a key step for organisms during evolution. The capacity to adapt from nutrient-rich to nutrient-poor environments led to the appearance of protein complexes regulating anabolic and catabolic pathways. The evolutionarily conserved kinase mTOR (mechanistic target of rapamycin) emerged as a crucial and central protein for regulating many different cellular functions in response to environmental changes.

Complete genome sequence of a psychotrophic Pseudarthrobacter sulfonivorans strain Ar51 (CGMCC 4.7316), a novel crude oil and multi benzene compounds degradation strain

Pseudarthrobacter sulfonivorans strain Ar51, a psychotrophic bacterium isolated from the Tibet permafrost of China, can degrade crude oil and multi benzene compounds efficiently in low temperature. Here we report the complete genome sequence of this bacterium. The complete genome sequence of Pseudarthrobacter sulfonivorans strain Ar51, consisting of a cycle chromosome with a size of 5.04Mbp and a cycle plasmid with a size of 12.39kbp. The availability of this genome sequence allows us to investigate the genetic basis of crude oil degradation and adaptation to growth in a nutrient-poor permafrost environment.

The General Stress Response Is Conserved in Long-Term Soil-Persistent Strains of Escherichia coli

Although Escherichia coli is generally considered to be predominantly a commensal of the gastrointestinal tract, a number of recent studies suggest that it is also capable of long-term survival and growth in environments outside the host. As the extraintestinal physical and chemical conditions are often different from those within the host, it is possible that distinct genetic adaptations may be required to enable this transition. Several studies have shown a trade-off between growth and stress resistance in nutrient-poor environments, with lesions in the rpoS locus, which encodes the stress sigma factor RpoS (σ(S)). In this study, we investigated a unique collection of long-term soil-persistent E. coli isolates to determine whether the RpoS-controlled general stress response is altered during adaptation to a nutrient-poor extraintestinal environment. The sequence of the rpoS locus was found to be highly conserved in these isolates, and no nonsense or frameshift mutations were detected. Known RpoS-dependent phenotypes, including glycogen synthesis and γ-aminobutyrate production, were found to be conserved in all strains. All strains expressed the full-length RpoS protein, which was fully functional using the RpoS-dependent promoter reporter fusion PgadX::gfp RpoS was shown to be essential for long-term soil survival of E. coli, since mutants lacking rpoS lost viability rapidly in soil survival assays. Thus, despite some phenotypic heterogeneity, the soil-persistent strains all retained a fully functional RpoS-regulated general stress response, which we interpret to indicate that the stresses encountered in soil provide a strong selective pressure for maintaining stress resistance, despite limited nutrient availability. Escherichia coli has been, and continues to be, used as an important indicator species reflecting potential fecal contamination events in the environment. However, recent studies have questioned the validity of this, since E. coli has been found to be capable of long-term colonization of soils. This study investigated whether long-term soil-persistent E. coli strains have evolved altered stress resistance characteristics. In particular, the study investigated whether the main regulator of genes involved in stress protection, the sigma factor RpoS, has been altered in the soil-persistent strains. The results show that RpoS stress protection is fully conserved in soil-persistent strains of E. coli They also show that loss of the rpoS gene dramatically reduces the ability of this organism to survive in a soil environment. Overall, the results indicate that soil represents a stressful environment for E. coli, and their survival in it requires that they deploy a full stress protection response.

Influence of Physiological Stress on Nutrient Stoichiometry in Larval Amphibians.

Exposure to environmental stressors alters animal phenotypes as well as nutrient metabolism, assimilation, and excretion. While stress-induced shifts in nutrient processes are known to alter organismal carbon (C) and nitrogen (N) stoichiometry, there has been little exploration of how environmental factors influence phosphorous (P). A better understanding of how P cycling varies with animal physiological state may provide insight into across-scale processes, because P is essential to animal function and ecological processes such as production and decomposition. We tested the effects of predator stress and exogenous glucocorticoids on C∶N∶P stoichiometry of larval amphibians. Glucocorticoids altered nutrient stoichiometry, apparently by modulating ossification and renal function. This reduced whole-body P and significantly increased N∶P. Additionally, elevated glucocorticoids caused a long-term reduction in P excretion. This reduction may reflect an initial unmeasured loss of P that glucocorticoids induce over acute timescales. In contrast, exposure to predator cues had no effect on larval C∶N∶P stoichiometry, which highlights that different stressors have varied effects on the endocrine stress response. Predation, in particular, is ubiquitous in the environment; thus, larvae responding to predators have conserved mechanisms that likely prevent or minimize physiological disruption. These results demonstrate the differing physiological roles of N and P, distinct nutrient demands associated with amphibian metamorphosis, and the contrasting effects that different environmental factors have on the physiological stress response. Our results also suggest that anthropogenic changes to the environment that induce chronic stress in amphibians could affect the biogeochemistry of nutrient-poor environments where they may act as keystone species.

Glycerol outflow in Symbiodinium under osmotic and nitrogen stress

In marine nutrient-poor environments, the success of Symbiodinium–cnidarian symbioses depends on the translocation of photosynthetically fixed carbon to the host. However, the mechanisms involved in this translocation are not well understood. Glycerol has been identified in the literature as one of the main photosynthates translocated from symbiont to host. Considering that glycerol is a preferred regulatory osmolyte in many unicellular eukaryotes and exposure of isolated symbionts to host homogenate results in the liberation of glycerol, we investigated the potential role of glycerol and its release in Symbiodinium. We studied the response to high osmolarity in two cultured species of Symbiodinium, examining glycerol production, specific activity of the enzyme glycerol 3-phosphate dehydrogenase and expression of the coding gene. We also assessed the production of glycerol and glucose under osmotic stress and nitrogen depletion. Results showed that cells exposed to high osmolarity conditions induced the synthesis of glycerol, although it was not retained effectively inside cells. In addition, nitrogen depletion also induced the synthesis of glycerol, although values were an order of magnitude lower. Interestingly, a significant decrease in glucose levels was detected in osmotically stressed cultures and under low nitrogen, possibly associated with the storage of carbon. While glycerol is a metabolite induced by osmotic stress, our results do not support its role as osmolyte. We conclude that glycerol may have a role as a sink for reducing power to prevent feedback inhibition of photosynthesis, particularly under low nitrogen, conditions that may be prevalent in the symbiosis.

Species-Specific Effects of Ant Inhabitants on Bromeliad Nutrition.

Predator activities may lead to the accumulation of nutrients in specific areas of terrestrial habitats where they dispose of prey carcasses. In their feeding sites, predators may increase nutrient availability in the soil and favor plant nutrition and growth. However, the translocation of nutrients from one habitat to another may depend on predator identity and diet, as well as on the amount of prey intake. Here we used isotopic (15N) and physiological methods in greenhouse experiments to evaluate the effects of the identity of predatory ants (i.e., the consumption of prey and nest sites) on the nutrition and growth of the bromeliad Quesnelia arvensis. We showed that predatory ants with protein-based nutrition (i.e., Odontomachus hastatus, Gnamptogenys moelleri) improved the performance of their host bromeliads (i.e., increased foliar N, production of soluble proteins and growth). On the other hand, the contribution of Camponotus crassus for the nutritional status of bromeliads did not differ from bromeliads without ants, possibly because this ant does not have arthropod prey as a preferred food source. Our results show, for the first time, that predatory ants can translocate nutrients from one habitat to another within forests, accumulating nutrients in their feeding sites that become available to bromeliads. Additionally, we highlight that ant contribution to plant nutrition may depend on predator identity and its dietary requirements. Nest debris may be especially important for epiphytic and terrestrial bromeliads in nutrient-poor environments.

Dicranochaete – an enigmatic green alga with surprising adaptive capabilities

:Dicranochaete is a green coccoid alga with a spiny cap and a long branched seta that was described more than 100 yr ago from field samples. Although Dicranochaete has been repeatedly reported to be found on Sphagnum ‘leaves’ in peat bogs, our knowledge about its development is still fragmentary, and its phylogenetic affiliation remained controversial. To advance knowledge about this lesser-known alga, I used two Dicranochaete strains, grew them in a medium that mimics chemical properties of peat bogs and studied their life history and development. Furthermore, phylogenetic analyses using rDNA sequence comparisons were performed. My studies resulted in the following key observations: (1) Dicranochaete possesses a unique development that together with its characteristic morphology likely represents adaptations to the specific environment of peat bogs: the spiny cap, especially in early stages of algal development, presumably serves as a defence against predators. The seta provides an additional surface area to aid the uptake of nutrients, in particular phosphate. (2) Phylogenetic analyses identified Dicranochaete as a member of the Chaetopeltidales (Chlorophyceae). Moreover, a new species of Dicranochaete, Dicranochaete variabilis sp. nov., was erected, and the genus Dicranochaete Hieronymus (1890) was emended. In conclusion, this study provides new insights into the life history, developmental processes and phylogenetic position of Dicranochaete and provides insights into adaptation of epiphyllous microalgae to nutrient-poor environments (i.e. peat bogs).

Complete genome sequence of a psychotrophic Arthrobacter strain A3 (CGMCC 1.8987), a novel long-chain hydrocarbons producer

Arthrobacter strain A3, a psychotrophic bacterium isolated from the Tian Shan Mountain of China, can degrade the cellulose and synthesis the long-chain hydrocarbons efficiently in low temperature. Here we report the complete genome sequence of this bacterium. The complete genome sequence of Arthrobacter strain A3, consisting of a cycle chromosome with a size of 4.26 Mbp and a cycle plasmid with a size of 194kbp. In this genome, a hydrocarbon biosynthesis gene cluster (oleA, oleB/oleC and oleD) was identified. To resistant the extreme environment, this strain contains a unique mycothiol-biosynthetic pathway (mshA-D), which has not been found in other Arthrobacter species before. The availability of this genome sequence allows us to investigate the genetic basis of adaptation to growth in a nutrient-poor permafrost environment and to evaluate of the biofuel-synthetic potential of this species.

Predation and selection for antibiotic resistance in natural environments.

Genes encoding resistance to antibiotics appear, like the antibiotics themselves, to be ancient, originating long before the rise of the era of anthropogenic antibiotics. However, detailed understanding of the specific biological advantages of antibiotic resistance in natural environments is still lacking, thus limiting our efforts to prevent environmental influx of resistance genes. Here, we propose that antibiotic-resistant cells not only evade predation from antibiotic producers but also take advantage of nutrients released from cells that are killed by the antibiotic-producing bacteria. Thus, predation is potentially an important mechanism for driving antibiotic resistance during slow or stationary phase of growth when nutrients are deprived. This adds to explain the ancient nature and widespread occurrence of antibiotic resistance in natural environments unaffected by anthropogenic antibiotics. In particular, we suggest that nutrient-poor environments including indoor environments, for example, clean rooms and intensive care units may serve as a reservoir and source for antibiotic-producing as well as antibiotic-resistant bacteria.