The dead zones: oxygen-starved coastal waters.
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After the great Mississippi River flood of 1993, the hypoxic (or low-oxygen) "dead zone" in the Gulf of Mexico more than doubled its size, reaching an all-time high of over 7,700 square miles in July of 1999. Scientists attribute the Gulf of Mexico dead zone largely to nutrient runoff from agriculture in the Mississippi River basin. During the warm months, these nutrients fuel eutrophication, or high organic production, causing large algal blooms. When the algae decay, the result is hypoxia. Reports of such hypoxic events around the world have been increasing since the mid 1960s. Eutrophication and hypoxia have resulted in mortality of bottom-dwelling life in dozens of marine ecosystems and have stressed fisheries worldwide. Some algal blooms can alter the function of coastal ecosystems or, potentially, threaten human health. Anthropogenic nutrient loading from sources such as agriculture, fossil fuel emissions, and climate events is believed to be related to the global increase in frequency, size, and duration of certain algal blooms. (+info)
Recent developments in the biochemistry and ecology of enhanced biological phosphorus removal.
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Most of the genes encoding the enzymes involved in polyP synthesis and degradation and in phosphate transport have been studied in various Gram-negative bacteria. Progress has also been made in studying the biochemical mechanisms underlying the process of enhanced biological phosphorus removal (EBPR), in particular in lab-scale systems fed with acetate or acetate plus glucose as the sole carbon and energy sources. By applying 13C-NMR, previous models concerning anaerobic carbon metabolism have been advanced and the role of glycogen in providing reducing equivalents in EBPR is definitely demonstrated. The role of the citric acid cycle in supplying reducing equivalents for the conversion of acetyl-CoA into poly-beta-hydroxybutyrate and poly-beta-hydroxyvalerate has been discussed. An incomplete citric acid cycle has been proposed to provide a small part of the reducing equivalents. Polyphosphate:AMP phosphotransferase and polyphosphatase were readily detectable in EBPR sludge fed with acetate plus glucose, but polyphosphate kinase remained undetected. In a lab-scale EBPR system, fed for several months with only acetate as carbon source, a Rhodocyclus-like bacterium (R6) was highly enriched and is therefore probably responsible for EBPR in systems fed with acetate only. This R6-type bacterium was however also present in other EBPR sludges (but to a lesser extent), and may therefore play an important role in EBPR in general. This organism accumulates polyhydroxyalkanoates anaerobically and polyP under aerobic conditions. Unlike members of the genus Rhodocyclus, bacterium R6 cannot grow phototrophically. Therefore a provisional new genus Candidatus and species Accumulibacter phosphatis was proposed. (+info)
Microbial selection of polyphosphate-accumulating bacteria in activated sludge wastewater treatment processes for enhanced biological phosphate removal.
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Activated sludge processes with alternating anaerobic and aerobic conditions (the anaerobic-aerobic process) have been successfully used for enhanced biological phosphate removal (EBPR) from wastewater. It is known that polyphosphate-accumulating bacteria (PAB) play an essential role for EBPR in the anaerobic-aerobic process. The present paper reviews limited information available on the metabolism and the microbial community structure of EBPR, highlighting the microbial ecological selection of PAB in EBPR processes. Exposure of microorganisms to alternate carbon-rich anaerobic environments and carbon-poor aerobic environments in the anaerobic-aerobic process induces the key metabolic characteristics of PAB, which include organic substrate uptake followed by its conversion to stored polyhydroxyalkanoate (PHA) and hydrolysis of intracellular polyphosphate accompanied by subsequent Pi release under anaerobic conditions. Intracellular glycogen is assumed to function as a regulator of the redox balance in the cell. Storage of glycogen is a key strategy for PAB to maintain the redox balance in the anaerobic uptake of various organic substrates, and hence to win in the microbial selection. Acinetobacter spp., Microlunatus phosphovorus, Lampropedia spp., and the Rhodocyclus group have been reported as candidates of PAB. PAB may not be composed of a few limited genospecies, but involve phylogenetically and taxonomically diverse groups of bacteria. To define microbial community structure of EBPR processes, it is needed to look more closely into the occurrence and behavior of each species of PAB in various EBPR processes mainly by molecular methods because many of PAB seem to be impossible to culture. (+info)
Evaluation of F-specific RNA bacteriophage as a candidate human enteric virus indicator for bivalve molluscan shellfish.
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Escherichia coli is a widely utilized indicator of the sanitary quality of bivalve molluscan shellfish sold for human consumption. However, it is now well documented that shellfish that meet the E. coli standards for human consumption may contain human enteric viruses that cause gastroenteritis and hepatitis. In this study we investigated using F-specific RNA bacteriophage (FRNA bacteriophage) to indicate the likely presence of such viruses in shellfish sold for consumption. FRNA bacteriophage and E. coli levels were determined over a 2-year period for oysters (Crassostrea gigas) harvested from four commercial sites chosen to represent various degrees of sewage pollution. Three sites were classified as category B sites under the relevant European Community (EC) Directive (91/492), which required purification (depuration) of oysters from these sites before sale. One site was classified as a category A site, and oysters from this site could be sold directly without further processing. Samples were tested at the point of sale following commercial processing and packaging. All of the shellfish complied with the mandatory EC E. coli standard (less than 230 per 100 g of shellfish flesh), and the levels of contamination for more than 90% of the shellfish were at or below the level of sensitivity of the assay (20 E. coli MPN per 100 g), which indicated good quality based on this criterion. In contrast, FRNA bacteriophage were frequently detected at levels that exceeded 1,000 PFU per 100 g. High levels of FRNA bacteriophage contamination were strongly associated with harvest area fecal pollution and with shellfish-associated disease outbreaks. Interestingly, FRNA bacteriophage contamination exhibited a marked seasonal trend that was consistent with the trend of oyster-associated gastroenteritis in the United Kingdom. The correlation between FRNA bacteriophage contamination and health risk was investigated further by using a reverse transcription-PCR assay for Norwalk-like virus (NLV). NLV contamination of oysters was detected only at the most polluted site and also exhibited a seasonal trend that was consistent with the trend of FRNA bacteriophage contamination and with the incidence of disease. The results of this study suggest that FRNA bacteriophage could be used as viral indicators for market-ready oysters. (+info)
Electricity generation in microbial fuel cells using neutral red as an electronophore.
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Neutral red (NR) was utilized as an electron mediator in microbial fuel cells consuming glucose to study both its efficiency during electricity generation and its role in altering anaerobic growth and metabolism of Escherichia coli and Actinobacillus succinogenes. A study of chemical fuel cells in which NADH, NR, and ferricyanide were the electron donor, the electronophore, and the electron acceptor, respectively, showed that electrical current produced from NADH was proportional to the concentration of NADH. Fourfold more current was produced from NADH in chemical fuel cells when NR was the electron mediator than when thionin was the electron mediator. In microbial fuel cells in which E. coli resting cells were used the amount of current produced from glucose when NR was the electron mediator (3.5 mA) was 10-fold more than the amount produced when thionin was the electron mediator (0.4 mA). The amount of electrical energy generated (expressed in joules per mole of substrate) and the amount of current produced from glucose (expressed in milliamperes) in NR-mediated microbial fuel cells containing either E. coli or A. succinogenes were about 10- and 2-fold greater, respectively, when resting cells were used than when growing cells were used. Cell growth was inhibited substantially when these microbial fuel cells were making current, and more oxidized end products were formed under these conditions. When sewage sludge (i.e., a mixed culture of anaerobic bacteria) was used in the fuel cell, stable (for 120 h) and equivalent levels of current were obtained with glucose, as observed in the pure-culture experiments. These results suggest that NR is better than other electron mediators used in microbial fuel cells and that sludge production can be decreased while electricity is produced in fuel cells. Our results are discussed in relation to factors that may improve the relatively low electrical efficiencies (1.2 kJ/mol) obtained with microbial fuel cells. (+info)
Yeast spores seem to be involved in biological phosphate removal: a microscopic in situ case study.
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The principal polyphosphate-accumulating organism (PAO) in a biological-phosphate-removal activated-sludge process was assessed microscopically. The organism was recognized by its distinct morphotype most easily after polyphosphate staining. The PAO occurred in large, homogeneous clusters. The cells of the PAO were the biggest cells abounding in the sludge--clearly bigger than average sludge bacteria. Typical of the principal PAO was a variation of cell size, even in fresh sludge. In acetate minimal medium containing ampicillin, the original principal PAO clusters were converted to clusters of clearly larger, polyphosphate-containing, vegetative yeast-like cells. Cycloheximide addition inhibited this and caused flock disintegration, disappearance of the principal PAO clusters and growth of free bacteria. The cell wall of the principal PAO was not of the usual bacterial character. It showed anomalous Gram staining, stained for chitin (not found in bacteria) and bound concanavalin A, like cell walls of many yeasts. In addition, the PAO cell wall was resistant to lysozyme, but sensitive to an enzyme mixture that lyses yeast cell walls. It was concluded that the principal PAO cells in the studied sludge were clustered spores of a yeast. (+info)
Three isolates of novel polyphosphate-accumulating gram-positive cocci, obtained from activated sludge, belong to a new genus, Tetrasphaera gen. nov., and description of two new species, Tetrasphaera japonica sp. nov. and Tetrasphaera australiensis sp. nov.
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Two isolates of Gram-positive cocci (Ben 109T and Ben 110) which could accumulate polyphosphate and were microscopically similar in appearance to so-called 'G-bacteria', appearing as tetrads, were isolated from samples of activated sludge biomass by micromanipulation and grown in axenic culture. On the basis of their phenotypic and chemotaxonomic characters and 16S rDNA sequences, these isolates, together with strain T1-X7T isolated and described previously in Japan, belong to a new genus. These isolates are phylogenetically different from Tessaracoccus bendigoensis, Friedmanniella spumicola and Friedmanniella capsulata, Gram-positive cocci isolated previously in this laboratory. They are characterized by type A1 gamma peptidoglycan, with meso-diaminopimelic acid as the diagnostic diamino acid. The main cellular fatty acid of Ben 109T, Ben 110 and T1-X7T is 14-methylpentadecanoic acid (i-C16:0). The major menaquinones of Ben 109T are MK-8(H4), with MK-8(H2) and MK-8 in trace amounts. In Ben 110 MK-8(H4) and MK-6(H4) are the major menaquinones, while T1-X7T has MK-8(H4), MK-7(H4) and MK-6(H4) as its menaquinones. All three contain phosphatidylinositol, phosphatidylglycerol and diphosphatidylglycerol as their polar lipids. These properties, together with 16S rDNA sequence data, suggest that they all belong to a single new genus for which the name Tetrasphaera gen. nov. is proposed. However, the lipid, cellular fatty acid profiles and DNA-DNA similarity data suggest that Ben 109T and Ben 110 are sufficiently different from T1-X7T to represent a different species of the genus Tetrasphaera. Strain T1-X7T represents the type species Tetrasphaera japonica sp. nov. of this new genus, and strains Ben 109T and Ben 110 belong to the other species, Tetrasphaera australiensis sp. nov. (+info)
'Candidatus Nostocoida limicola', a filamentous bacterium from activated sludge.
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Five strains of 'Candidatus Nostocoida limicola' were isolated by micromanipulation from two activated sludge plants. Two (Ben17 and Ben18) were from Sunbury, Victoria, Australia, and three (Ben67, Ver1 and Ver2) were from Verona, Italy. The near complete 16S rDNA sequences were determined for five strains and the phylogenetic location of this important bulking filament in the actinomycete subphylum is reported for the first time. Phylogenetically, the Ben strains formed one group with 99.4% 16S rDNA similarity, and the Ver strains formed another with 99.9% 16S rDNA similarity. The mean similarity between the two groups was 97.4%. By 16S rDNA comparison, the closest relative to all strains was Terrabacter sp. strain DPO1361 (95.0-95.5% identical). On R2A medium, all strains generally grew as short filaments or clumps of cocci, whereas on glucose sulfide (GS) medium, all grew as irregular twisting filaments comprising Gram-positive and Gram-negative cells, which is close to their in situ morphology. Polyphosphate was stored either as granules (R2A) or throughout the trichomes (GS). None of the strains could grow without added nitrogen, reduce nitrate to nitrogen gas or grow anaerobically, whereas all could grow at 15-30 degrees C, produce catalase and reduce nitrate to nitrite. All were inactive in the Hugh & Leifson test. This paper describes 'Candidatus Nostocoida limicola'. (+info)