Series Of Organisms Research Articles

A Review of N-(1,3-Dimethylbutyl)-N'-phenyl-p-Phenylenediamine (6PPD) and Its Derivative 6PPD-Quinone in the Environment.

As an antioxidant and antiozonant, N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) is predominantly used in the rubber industry to prevent degradation. However, 6PPD can be ozonated to generate a highly toxic transformation product called N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6PPD-quinone), which is toxic to aquatic and terrestrial organisms. Thus, 6PPD and 6PPD-quinone, two emerging contaminants, have attracted extensive attention recently. This review discussed the levels and distribution of 6PPD and 6PPD-quinone in the environment and investigated their toxic effects on a series of organisms. 6PPD and 6PPD-quinone have been widely found in air, water, and dust, while data on soil, sediment, and biota are scarce. 6PPD-quinone can cause teratogenic, developmental, reproductive, neuronal, and genetic toxicity for organisms, at environmentally relevant concentrations. Future research should pay more attention to the bioaccumulation, biomagnification, transformation, and toxic mechanisms of 6PPD and 6PPD-quinone.

Hydrogen gas as a central on-off functional switch of reversible metabolic arrest – New perspectives for biotechnological applications

Metabolism is the sum of all chemical reactions that sustain life. There is an ongoing effort to control metabolic rate, which correlates with the maximum lifespan potential and constitutes one of the oldest scientific questions. Herein, we report on the complete reversible arrest of cellular metabolism and cell growth in a series of organisms, from microalgae to yeast upon exposure to a 100 % hydrogen atmosphere. We also report a tolerance of the microalgae under these conditions against extreme stress conditions, like high salt concentrations. The addition of oxygen or air almost completely restores the metabolic rate and cell growth. Molecular dynamics simulations are employed to decipher this phenomenon at atomic scale. Various proteins, including photosynthetic and respiratory complexes (LHCII, cytochrome c5) are probed in the interaction with hydrogen. Exposure to hydrogen, as opposed to oxygen, decreases the fluctuations of protein residues indicating thermostability. According to the above mechanism, an absolute hydrogen atmosphere can preserve biological products (e.g. fruits) for a long time without consuming any energy. By combining biological, chemical and computational methods, in this research we provide the basis for future innovative studies and advances in the field of biotechnology.

Syntrophy in microbial fuel cells

Syntrophy has a pivotal role in the microbial degradation of organic compounds in methanogenic ecosystems (McInerney et al., 2009). Methanogenic degradation of organic compounds is a sequential process: a series of organisms is involved in the various conversion steps of these compounds into methane and carbon dioxide (Dolfing, 1988). Typically, the product of one conversion step is the substrate for the next organism in the chain; each organism lives off the waste product(s) of its predecessor. Their defining characteristic as it relates to syntrophy is that in many of these associations the producer is critically dependent on the activities of the consumer (Schink and Stams, 2006): degradation of short chain volatile fatty acids like propionate and butyrate is only sustainable if the electrons produced in the process are removed by other organisms (Dolfing, 2013). This concept was first put forward by Bryant et al. (1967) who famously invoked thermodynamics to rationalize their observation that ethanol degradation could only sustain growth of an ethanol degrader if the hydrogen produced in the process is removed by a hydrogenotrophic methanogen. Since then we have learned that interspecies hydrogen transfer is not the only mechanism to facilitate syntrophy: interspecies formate transfer and direct interspecies electron transfer (DIET) are distinct alternatives to the classical pathway (Stams and Plugge, 2009; Summers et al., 2010). Obviously, the very core value of syntrophy—the critical interdependency between producer and consumer—has not been challenged by this changing perspective. That is, until recently. Earlier this year Kimura and Okabe (2013) reported that Geobacter sulfurreducens PCA can oxidize acetate in what the authors labelled ‘a syntrophic cooperation' with Hydrogenophaga sp. strain AR20 in conjunction with an electrode as the final electron acceptor. However, close reading of their paper reveals that G. sulfurreducens PCA does not require the presence and activity of strain AR20 to perform this feat: in pure culture G. sulfurreducens PCA can also oxidize acetate in conjunction with an electrode as the final electron acceptor; the organism can grow on this reaction, as expected (Bond and Lovley, 2003). Thus G. sulfurreducens PCA does not critically depend on its partner, and the association between the two organisms is therefore not syntrophic. For the co-culture to be syntrophic, it would require that G. sulfurreducens ceases to be an electrogen, or more precisely ceases to be able to use electrodes as electron acceptor. The data put forward by Kimura and Okabe (2013) provide no evidence that this indeed the case, though they do indicate that G. sulfurreducens PCA benefits from the presence of Hydrogenophaga sp. strain AR20. It will be interesting to see to what extent the anode potential modulates the interactions between these two electrogens, and it is tempting to speculate that applying the ‘optimal' electrode potential may coax the co-culture into syntrophy. Morris et al. (2013) recently noted that in the literature on anaerobic ecosystems syntrophy is traditionally described in detailed mechanistic terms, making explanations of the concept rather wordy. They therefore propose to define syntrophy as ‘obligately mutualistic metabolism'. This definition indeed covers the very core value of syntrophy highlighted above—the critical interdependency between producer and consumer—but will not alleviate the need to highlight the (thermodynamic) rational behind this interdependency in anaerobic ecosystems. Interestingly, the host–bacterial mutualism in the human intestine (Backhed et al., 2005) and area of much current research (for a recent review, see for example Sommer and Backhed, 2013) also seems to fall within the realm of syntrophy. It is to be expected that the recent eye-openers on DIET and DIET-based syntrophic growth (Summers et al., 2010; Shrestha et al., 2013) will not only lead to more exciting work on this mechanism but will also give new impetus to the traditionally more biochemical and thermodynamical-oriented research on syntrophy via interspecies hydrogen and formate transfer (Stams and Plugge, 2009; Sieber et al., 2012). Surprisingly, little is known about the kinetics behind syntrophic interactions and the interplay between kinetics and thermodynamics (Dolfing and Tiedje, 1986; Dwyer et al., 1988; Stams et al., 2006). Microbial fuel cells are promising tools to tackle those issues, but traditional chemostat studies offer perspective as well, not only for studies on syntrophy but also for studies on other types of interactions like those between acetogenesis and methanogenesis (Lever, 2012; Oren, 2012). Given the long running times needed to obtain comprehensive data sets with chemostat systems, it seems prudent to start such studies with some modelling work to delineate at which dilution rates insightful results can be expected (Xu et al., 2011; Dolfing and Xu, 2012).

Spline models of biological population dynamics: How to estimate mortality rates for stage structured populations with dimorphic life histories

Nonparametric spline based models of stage structured population dynamics provide an effective way of decomposing observed population dynamics into birth and death rate processes. Currently available methodology only considers simple life histories in which all individuals pass through the same sequence of stages in the same way. This paper presents techniques for obtaining birth and death rates from structured population time series of organisms with complex life histories. For example, in many species males and females develop at the same rate in early stages, but differently in late stages. The models are motivated by the need to obtain birth and death rates for a pest subject to biocontrol by a parasitoid.

Production of extra-cellular slime by Staphylococcus epidermidis during stationary phase of growth: its association with adherence to implantable devices.

A method of optimising slime production produced by Staphylococcus epidermis and its quantitative assay was developed, which gave a preliminary indication of its identity and an assessment of the correlation between slime production and adherence of the organism to implants. After inducing vigorous growth in brain heart infusion broth to stationary phase, all nutrients were removed by washing and the organisms resuspended in sterile deionised water with added magnesium. After further incubation the culture was centrifuged and the supernatant reacted with alcian blue in 50 mM magnesium chloride/sodium acetate solution, and the amount of bound dye was measured spectrophotometrically at 620 nm after its resolubilisation using sodium dodecyl sulphate. Large quantities of slime were produced by some, but not all, strains. Preliminary electrophoresis of the slime showed mobility and staining similar to that of the glycosaminoglycans. Adherence was tested by growing strains in wells of tissue culture plates and aspirating the supernatant after incubation. After fixation and staining of adherent growth the amount of bound stain was determined spectrophotometrically after its elution with ethanol. In this series of organisms there was no correlation between the result of tests for adherence or production of extracellular slime, and no correlation between either of these and the clinical source of the organisms.

Relationships of the Actinomycetales

The evolutionary scheme herein proposed involves a series of organisms showing morphological and physiological relationships beginning with a sporangial ancestor with motile spores evolving to redu...

On Putrefactive Organisms1

On Putrefactive Organisms1

Biological Notes

NEW FRESH-WATER RHIZOPODS.—For many years the small group known as Actinophrys, first accurately described by Ehrenberg, remained somewhat isolated, distinguished among unicellular forms by its nearly constant spherical form, and the persistence of its straight radiating processes or “pseudopodia.” But in recent years a whole series of organisms has been described, and has attained sufficient prominence to constitute, with Actinophrys, an order denominated Heliozoa. Many interesting papers have appeared in the Archiv für mikroskopische Anatomie on these organisms, contributed by E. Hertwig, Lesser, Cienkowski, Greeff, and others; and in our own country Mr. W. Archer has been the most active and successful student of the Heliozoa, his papers having been principally published in the Quarterly Journal of Microscopical Science. From these one derives an idea of these animalcules as being the most complex of the free forms which possess pseudopodia, and are at the same time unicellular; they are neither multicellular and differentiated like the Radiolaria, nor organised like the ciliated Infusoria. While a few forms, as Actinophrys, are quite devoid of skeleton, most of them possess certain hard parts, consisting, it may be, of a single solid and globular piece, but in other cases of very minute rod-shaped spicules, sometimes siliceous, sometimes easily soluble. These are either disposed so as to invest the main body of the organism more or less closely, or radially, projecting as spines. When food is taken, these minute hard parts can be pushed aside to allow access to the central body-mass; and the same occurs when indigestible material is thrust out. Locomotion is usually very slow; most Heliozoans move by balancing themselves on the tips of their pseudopodia, and thus very gradually rolling onwards. Multiplication of the organisms is effected by division, either simple, or occurring after encystation. Some forms are remarkable for containing a great abundance of chlorophyll granules.