Nitrogen Forms Influence Microcystin Concentration and Composition via Changes in Cyanobacterial Community Structure

The eutrophication of freshwaters is a global health concern as lakes with excess nutrients are often subject to toxic cyanobacterial blooms. Although phosphorus is considered the main element regulating cyanobacterial biomass, nitrogen (N) concentration and more specifically the availability of different N forms may influence the overall toxicity of blooms. In this study of three eutrophic lakes prone to cyanobacterial blooms, we examined the effects of nitrogen species and concentrations and other environmental factors in influencing cyanobacterial community structure, microcystin (MC) concentrations and MC congener composition. The identification of specific MC congeners was of particular interest as they vary widely in toxicity. Different nitrogen forms appeared to influence cyanobacterial community structure leading to corresponding effects on MC concentrations and composition. Total MC concentrations across the lakes were largely explained by a combination of abiotic factors: dissolved organic nitrogen, water temperature and ammonium, but Microcystis spp. biomass was overall the best predictor of MC concentrations. Environmental factors did not appear to affect MC congener composition directly but there were significant associations between specific MC congeners and particular species. Based on redundancy analyses (RDA), the relative biomass of Microcystis aeruginosa was associated with MC-RR, M. wesenbergii with MC-LA and Aphanizomenon flos-aquae with MC-YR. The latter two species are not generally considered capable of MC production. Total nitrogen, water temperature, ammonium and dissolved organic nitrogen influenced the cyanobacterial community structure, which in turn resulted in differences in the dominant MC congener and the overall toxicity.     

Complete genome sequence of Riemerella anatipestifer type strain (ATCC 11845)

Riemerella anatipestifer (Hendrickson and Hilbert 1932) Segers et al. 1993 is the type species of the genus Riemerella, which belongs to the family Flavobacteriaceae. The species is of interest because of the position of the genus in the phylogenetic tree and because of its role as a pathogen of commercially important avian species worldwide. This is the first completed genome sequence of a member of the genus Riemerella. The 2,155,121 bp long genome with its 2,001 protein-coding and 51 RNA genes consists of one circular chromosome and is a part of the Genomic Encyclopedia of Bacteria and Archaea project.     

Complete genome sequence of Cellulophaga algicola type strain (IC166)

Cellulophaga algicola Bowman 2000 belongs to the family Flavobacteriaceae within the phylum 'Bacteroidetes' and was isolated from Melosira collected from the Eastern Antarctic coastal zone. The species is of interest because its members produce a wide range of extracellular enzymes capable of degrading proteins and polysaccharides with temperature optima of 20-30°C. This is the first completed genome sequence of a member of the genus Cellulophaga. The 4,888,353 bp long genome with its 4,285 protein-coding and 62 RNA genes consists of one circular chromosome and is a part of the Genomic Encyclopedia of Bacteria and Archaea project.     

Complete genome sequence of Desulfurococcus mucosus type strain (O7/1)

Desulfurococcus mucosus Zillig and Stetter 1983 is the type species of the genus Desulfurococcus, which belongs to the crenarchaeal family Desulfurococcaceae. The species is of interest because of its position in the tree of life, its ability for sulfur respiration, and several biotechnologically relevant thermostable and thermoactive extracellular enzymes. This is the third completed genome sequence of a member of the genus Desulfurococcus and already the 8(th) sequence from a member the family Desulfurococcaceae. The 1,314,639 bp long genome with its 1,371 protein-coding and 50 RNA genes is a part of the Genomic Encyclopedia of Bacteria and Archaea project.     

Adipose Triglyceride Lipase Is Implicated in Fuel- and Non-fuel-stimulated Insulin Secretion

Reduced lipolysis in hormone-sensitive lipase-deficient mice is associated with impaired glucose-stimulated insulin secretion (GSIS), suggesting that endogenous β-cell lipid stores provide signaling molecules for insulin release. Measurements of lipolysis and triglyceride (TG) lipase activity in islets from HSL^−/− mice indicated the presence of other TG lipase(s) in the β-cell. Using real time-quantitative PCR, adipose triglyceride lipase (ATGL) was found to be the most abundant TG lipase in rat islets and INS832/13 cells. To assess its role in insulin secretion, ATGL expression was decreased in INS832/13 cells (ATGL-knockdown (KD)) by small hairpin RNA. ATGL-KD increased the esterification of free fatty acid (FFA) into TG. ATGL-KD cells showed decreased glucose- or Gln + Leu-induced insulin release, as well as reduced response to KCl or palmitate at high, but not low, glucose. The K_ATP-independent/amplification pathway of GSIS was considerably reduced in ATGL-KD cells. ATGL^−/− mice were hypoinsulinemic and hypoglycemic and showed decreased plasma TG and FFAs. A hyperglycemic clamp revealed increased insulin sensitivity and decreased GSIS and arginine-induced insulin secretion in ATGL^−/− mice. Accordingly, isolated islets from ATGL^−/− mice showed reduced insulin secretion in response to glucose, glucose + palmitate, and KCl. Islet TG content and FFA esterification into TG were increased by 2-fold in ATGL^−/− islets, but glucose usage and oxidation were unaltered. The results demonstrate the importance of ATGL and intracellular lipid signaling for fuel- and non-fuel-induced insulin secretion.Free fatty acids (FFA)⁵ and other lipid molecules are important for proper glucose-stimulated insulin secretion (GSIS) by β-cells. Thus, deprivation of fatty acids (FA) in vivo (1) diminishes GSIS, whereas a short term exposure to FFA enhances it (1–3). In contrast, a sustained provision of FA, particularly in the presence of high glucose in vitro, is detrimental to β-cells in that it reduces insulin gene expression (4) and secretion (5) and induces β-cell apoptosis (6). The FA supply to the β-cells can be from exogenous sources, such as plasma FFAs and lipoproteins, or endogenous sources, such as intracellular triglyceride (TG) stores. Studies from our laboratory (7–10) and others (11, 12) support the concept that the hydrolysis of endogenous TG plays an important role in fuel-induced insulin secretion because TG depletion with leptin (13) or inhibition of TG lipolysis by lipase inhibitors such as 3,5-dimethylpyrazole (7) or orlistat (11, 12) markedly curtail GSIS in rat islets. Furthermore, mice with β-cell-specific knock-out of hormone-sensitive lipase (HSL), which hydrolyzes both TG and diacylglycerol (DAG), show defective first phase GSIS in vivo and in vitro (14).Lipolysis is an integral part of an essential metabolic pathway, the TG/FFA cycle, in which FFA esterification onto a glycerol backbone leading to the synthesis of TG is followed by its hydrolysis with the release of the FFA that can then be re-esterified. Intracellular TG/FFA cycling is known to occur in adipose tissue of rats and humans (15, 16) and also in liver and skeletal muscle (17). It is generally described as a “futile cycle” as it leads to the net hydrolysis of ATP with the generation of heat (18). However, several studies have shown that this cycle has important functions in the cell. For instance, in brown adipose tissue, it contributes to overall thermogenesis (17, 19). In islets from the normoglycemic, hyperinsulinemic, obese Zucker fatty rat, increased GSIS is associated with increased glucose-stimulated lipolysis and FA esterification, indicating enhanced TG/FFA cycling (10). Stimulation of lipolysis by glucose has also been observed in isolated islets from normal rats (12) and HSL^−/− mice (8) indicating the presence of glucose-responsive TG/FFA cycling in pancreatic β-cells.The identity of the key lipases involved in the TG/FFA cycle in pancreatic islets is uncertain. HSL is expressed in islets (20), is up-regulated by long term treatment with elevated glucose (21), and is associated with insulin secretory granules (22). In addition, our earlier results suggested that elevated HSL expression correlates with augmented TG/FFA cycling in islets of Zucker fatty rats (10). However, it appears that other lipases may contribute to lipolysis and the regulation of GSIS in islet tissue. Thus, results from studies using HSL^−/− mice showed unaltered GSIS (8, 23), except in fasted male mice (8, 9) in which lipolysis was decreased but not abolished. Furthermore, HSL^−/− mice show residual TG lipase activity (8) indicating the presence of other TG lipases.Recently, adipocyte triglyceride lipase (ATGL; also known as Desnutrin, TTS-2, iPLA₂-ζ, and PNPLA2) (24–26) was found to account for most if not all of the residual lipolysis in HSL^−/− mice (26, 27). Two homologues of ATGL, Adiponutrin and GS2, have been described in adipocytes (24). All three enzymes contain a patatin-like domain with broad lipid acyl-hydrolase activity. However, it is not known if adiponutrin and GS2 are actually TG hydrolases. An additional lipase, TG hydrolase or carboxylesterase-3, has been identified in rat adipose tissue (28, 29). Although the hydrolysis of TG is catalyzed by all these lipases, HSL can hydrolyze both TG and DAG, the latter being a better substrate (30).In this study, we observed that besides HSL, ATGL (31), adiponutrin, and GS2 are expressed in rat islets and INS832/13 cells, with ATGL being the most abundant. We then focused on the role of ATGL in fuel-stimulated insulin secretion in two models, INS832/13 β-cells in which ATGL expression was reduced by RNA interference-knockdown (ATGL-KD) and ATGL^−/− mice.     

Intracellular dynamics of archaeal FANCM homologue Hef in response to halted DNA replication

Hef is an archaeal member of the DNA repair endonuclease XPF (XPF)/Crossover junction endonuclease MUS81 (MUS81)/Fanconi anemia, complementation group M (FANCM) protein family that in eukaryotes participates in the restart of stalled DNA replication forks. To investigate the physiological roles of Hef in maintaining genome stability in living archaeal cells, we studied the localization of Hef–green fluorescent protein fusions by fluorescence microscopy. Our studies revealed that Haloferax volcanii Hef proteins formed specific localization foci under regular growth conditions, the number of which specifically increased in response to replication arrest. Purification of the full-length Hef protein from its native host revealed that it forms a stable homodimer in solution, with a peculiar elongated configuration. Altogether our data indicate that the shape of Hef, significant physicochemical constraints and/or interactions with DNA limit the apparent cytosolic diffusion of halophilic DNA replication/repair complexes, and demonstrate that Hef proteins are dynamically recruited to archaeal eukaryotic-like chromatin to counteract DNA replication stress. We suggest that the evolutionary conserved function of Hef/FANCM proteins is to enhance replication fork stability by directly interacting with collapsed replication forks.     

Complete genome sequence of Deinococcus maricopensis type strain (LB-34)

Deinococcus maricopensis (Rainey and da Costa 2005) is a member of the genus Deinococcus, which is comprised of 44 validly named species and is located within the deeply branching bacterial phylum Deinococcus-Thermus. Strain LB-34(T) was isolated from a soil sample from the Sonoran Desert in Arizona. Various species of the genus Deinococcus are characterized by extreme radiation resistance, with D. maricopensis being resistant in excess of 10 kGy. Even though the genomes of three Deinococcus species, D. radiodurans, D. geothermalis and D. deserti, have already been published, no special physiological characteristic is currently known that is unique to this group. It is therefore of special interest to analyze the genomes of additional species of the genus Deinococcus to better understand how these species adapted to gamma- or UV ionizing-radiation. The 3,498,530 bp long genome of D. maricopensis with its 3,301 protein-coding and 66 RNA genes consists of one circular chromosome and is a part of the Genomic Encyclopedia of Bacteria and Archaea project.     

Effect of artificial aeration and macrophyte species on nitrogen cycling and gas flux in constructed wetlands

Constructed wetlands (CWs) are efficient at removing excessive nutrients from wastewaters. However, this removal often results in the flux of important greenhouse gases (GHG), such as nitrous oxide (N₂O), carbon dioxide (CO₂) and methane (CH₄) that could mitigate the environmental benefits of CWs. We studied the efficiency of artificial aeration and 2 different macrophyte species (Phragmites australis, Typha angustifolia) on the removal and transformations of nitrogen and GHG gas flux using CW mesocosms supplied with 60 L m^?2 d^?1 of wastewater. Removal of total nitrogen (TN) and dissolved organic nitrogen (DON) was generally high in all beds but resulted in a net production of oxidized nitrogen (NO_y) in aerated CW mesocosms as compared to ammonium (NH₄⁺) in non-aerated units. Aerated units emitted less N₂O when planted with P. australis or left unplanted. Aerated beds and planted mesocosms had lower CH₄ fluxes than non-aerated units and unplanted beds, respectively. Our study suggests that planted systems with artificial aeration have the overall best performances in that they lead to a reduction of GHG flux and promote the release of NO_y over NH₄⁺ in their effluents.     

Pathogenicity in the tubercle bacillus: molecular and evolutionary determinants

In contrast to the great majority of mycobacterial species that are harmless saprophytes, Mycobacterium tuberculosis and other closely related tubercle bacilli have evolved to be among the most important human and animal pathogens. The need to develop new strategies in the fight against tuberculosis (TB) and related diseases has fuelled research into the evolutionary success of the M. tuberculosis complex members. Amongst the various disciplines, genomics and functional genomics have been instrumental in improving our understanding of these organisms. In this review we will present some of the recent key findings on molecular determinants of mycobacterial pathogenicity and attenuation, the evolution of M. tuberculosis, genome dynamics, antigen mining for improved diagnostic and subunit antigens, and finally the identification of novel drug targets. The genomics revolution has changed the landscape of TB research, and now underpins our renewed efforts to defeat this deadly pathogen.