Drinking water microbiology — from measurement to management

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Ipso-substitution — the hidden gate to xenobiotic degradation pathways

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Whatever happened to the ‘microtrabecular concept’?

Keith Porter culminated his stellar career as the founding father of biological electron microscopy by acquiring, in the late 1970s, a high-voltage electron microscope (HVEM). With this magnificent instrument he examined whole-mounts of cultured cells, and perceived within them a structured cytoplasmic matrix he named the "microtrabecular lattice". Over the next decade Porter published a series of studies, together with a team of outstanding young colleagues, which elaborated his broader "microtrabecular concept." This concept posited that microtrabeculae were real physical entities that represented the fundamental organization the cytoplasm, and that they were the physical basis of cytoplasmic motility and of cell-shape determination. The present review presents Porter's original images of microtrabeculae, after conversion to a more interpretable "digital-anaglyph" form, and discusses the rise and fall of the microtrabecular concept. Further, it explains how the HVEM images of microtrabeculae finally came to be considered as an artifact of the preparative methods Porter used to prepare whole cells for HVEM. Still, Keith's "microtrabecular concept" foretold of our current appreciation of the complexity and pervasiveness of the cytoskeleton, which has now been found by more modern methods of EM to actually be the fundamental organizing principle of the cytoplasmic matrix. During the impending eclipse of Porter's microtrabecular concept in the late 1980s, many of Keith's colleagues fondly described the cell as being filled, not with protoplasm, but with "Porterplasm." Despite the fact that Keith's view was clouded by the methods of his time, it would be fitting and apt to retain this name, still today, for the ordered matrix of cytoskeletal macromolecules that exists in the living cell. In the end, the story of what happened to Porter's microtrabecular concept should be an object lesson in scientific hubris that should humble and inform all of us in cell biology, even today--particularly when we begin to think that our most recent methods and observations are achieving "the last word".     

Candidiasis — Do we need to fight or to tolerate the<Emphasis Type="Italic">Candida</Emphasis> fungus?

Candidiases, infections caused by germination forms of the Candida fungus, represent a heterogeneous group of diseases from systemic infection, through mucocutaneous form, to vulvovaginal form. Although caused by one organism, each form is controlled by distinct host immune mechanisms. Phagocytosis by polymorphonuclears and macrophages is generally accepted as the host immune mechanism for Candida elimination. Phagocytes require proinflammatory cytokine stimulation which could be harmful and must be regulated during the course of infection by the activity of CD8+ and CD4+ T cells. In the vaginal tissue the phagocytes are inefficient and inflammation is generally an unwanted reaction because it could damage mucosal tissue and break the tolerance to common vagina antigens including the otherwise saprophyting Candida yeast. Recurrent form of vulvovaginal candidiasis is probably associated with breaking of such tolerance. Beside the phagocytosis, specific antibodies, complement, and mucosal epithelial cell comprise Candida eliminating immune mechanisms. They are regulated by CD4+ and CD8+ T cells which produce cytokines IL-12, IFN-gamma, IL-10, TGF-beta, etc. as the response to signals from dendritic cells specialized to sense actual Candida morphotypes. During the course of Candida infection proinflammatory signals (if initially necessary) are replaced successively by antiinflammatory signals. This balance is absolutely distinct during each candidiasis form and it is crucial to describe and understand the basic principles before designing new therapeutic and/or preventive approaches.     

‘Accelerated aging’: a primrose path to insight?

Organism envy afflicts most researchers who work on aging in mice; how frustrating it is to see the worm and fly biologists nail down milestone after milestone, citation after citation! Surely genetic trickery can produce mice that age in a comparable jiffy? Alas, our near‐total ignorance of what times the aging process makes it hard to guess what genes to tweak, if indeed aging can be mimicked a presto. Building a case that a given short‐lived mutant ages quickly is a steep and thorny path, requiring more than just plucking a symptom here and there from a list of things that sometimes go wrong in old people or old mice. The hallmark of aging is that a lot goes wrong more or less at the same time, in 2‐year‐old mice, 10‐year‐old dogs and 70‐year‐old people. Finding ways to damage one or two systems in a 6‐week or 6‐month‐old mouse is not too hard to do, but the implications of such studies for improved understanding of aging per se are at best indirect and at worst imaginary and distracting.     

Gα<Subscript>13</Subscript> is closely related to hematopoiesis in zebrafish

Heterotrimeric guanine nucleotide-binding regulatory proteins (G proteins) function as signal transducers and control many different physiologic processes. G proteins can be grouped into four families: G_s, G_i, G_q and G₁₂. Gα₁₃ belongs to the G₁₂ family. In zebrafish, there are two isoforms of Gα₁₃: Gα₁₃a and Gα₁₃b. We show here that knockdown of Gα₁₃b in zebrafish results in hematopoietic and angiogenic defects. The Gα₁₃b morphants don’t show complete loss of expression of gata1, pu.1 or flk until 35 hpf suggests that Gα₁₃b is closely related to the development of hematopoietic cells. Further studies reveal that blood cells and vascular endothelial cells have undergone apoptosis through a p53-dependent pathway in Gα₁₃b-depleted embryos. Injection of p53 morpholino could partially rescue the phenotype of Gα₁₃b morphants. These data possibly demonstrate a new role for Gα₁₃ in cell survival.     

Does Nutrient Availability Regulate Seagrass Response to Elevated CO<Subscript>2</Subscript>?

Future increases in oceanic carbon dioxide concentrations (CO_2(aq)) may provide a benefit to submerged plants by alleviating photosynthetic carbon limitation. However, other environmental factors (for example, nutrient availability) may alter how seagrasses respond to CO_2(aq) by regulating the supply of additional resources required to support growth. Thus, questions remain in regard to how other factors influence CO_2(aq) effects on submerged vegetation. This study factorially manipulated CO_2(aq) and nutrient availability, in situ, within a subtropical seagrass bed for 350 days, and examined treatment effects on leaf productivity, shoot density, above- and belowground biomass, nutrient content, carbohydrate storage, and sediment organic carbon (C_org). Clear, open-top chambers were used to replicate CO_2(aq) forecasts for the year 2100, whereas nutrient availability was manipulated via sediment amendments of nitrogen (N) and phosphorus (P) fertilizer. We provide modest evidence of a CO₂ effect, which increased seagrass aboveground biomass. CO_2(aq) enrichment had no effect on nutrient content, carbohydrate storage, or sediment C_org content. Nutrient addition increased leaf productivity and leaf N content, however did not alter above- or belowground biomass, shoot density, carbohydrate storage, or C_org content. Treatment interactions were not significant, and thus NP availability did not influence seagrass responses to elevated CO_2(aq). This study demonstrates that long-term carbon enrichment may alter the structure of shallow seagrass meadows, even in relatively nutrient-poor, oligotrophic systems.     

Is Muta™Mouse insensitive to clastogens?

Several studies suggest that Muta™Mouse is insensitive to clastogens, including the accompanying paper by Mahabir et al., which describes a study with bleomycin, camptothecin, m-AMSA (4′-(9-acridinylamino)-methanesulfon-m-anisidide) and its ortho-analogue, o-AMSA (4′-(9-acridinylamino)-methanesulfon-o-anisidide). Only camptothecin was clastogenic in Muta™Mouse and none of these four compounds induced mutations at the lacZ locus. However, to improve exposure, dose range-finding studies were performed in CD2F1 mice, the parental strain of Muta™Mouse. Male CD2F1 mice (n = 3) were treated with bleomycin (25–100 mg/kg bw, p.o. and i.p.), camptothecin (1–10 mg/kg bw p.o.) and m-AMSA (10–50 mg/kg bw p.o. and 1–5 mg/kg bw i.p.) for 5 days and blood was sampled on day 3 and/or day 6 for analysis by flow cytometry to determine % MN-RETs. Camptothecin (1 mg/kg bw, day 6) induced a 3.6-fold increase in % MN-RET (P < 0.05) but was toxic at higher doses. All day-3 camptothecin samples were positive (P < 0.05). Bleomycin was negative when administered p.o. but positive at all doses on both days when given i.p. (P < 0.05) whereas m-AMSA was negative when given i.p. or orally. Based on these results, male Muta™Mouse mice (5 per group) were dosed daily with bleomycin (50 mg/kg bw) for 5 days or with camptothecin (5 mg/kg bw) for 2 days. Peripheral blood was sampled 24 h after the final dose in each group and tissues were sampled 37 days later. Both compounds induced significant increases in % MN-RET, but only bleomycin induced a significant increase in MF (6-fold in liver, 4.5-fold in kidney and 2-fold in lung) compared with the untreated control. These studies support the view that Muta™Mouse is insensitive to compounds where the genotoxic mechanism of action is predominantly clastogenesis, but demonstrates that the peripheral blood micronucleus test is a useful adjunct to the transgenic gene-mutation assay.     

Translational biomaterials — the journey from the bench to the market — think ‘product’

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Elastic energy storage in β-sheets with application to F<Subscript>1</Subscript>-ATPase

We present a methodology for obtaining the elastic properties of protein motifs. We combine the use of interpolated structures (IS), molecular dynamics (MD) and collective coordinates to deduce the elastic properties of the -sheet in F₁ ATPase. We find that about 3.5 kcal/mol (6 k_BT at room temperature) of elastic energy is stored in the -sheet as the -subunit undergoes its hinge bending motion, in good agreement with the finite element model of Wang and Oster [Nature (1998) 396:279–282]. The technique should be useful for -sheets in other proteins and aid in the construction of phenomenological models for molecular motors that are computationally prohibitive for MD alone.     

β<Subscript>2</Subscript>-adrenergic receptor maladaptations to high power resistance exercise overreaching

The effects of a recovery drink on overreaching induced by high frequency, high power resistance exercise was assessed. Resistance trained men were assigned to a supplemented (SUP, n = 8), placebo (PL, n = 3) or control (CON, n = 6) groups. All groups completed two weeks of familiarization training using the barbell squat. In week three, SUP and PL performed ten sets of five repetitions of speed squats twice daily, for a total of 15 training sessions. CON maintained their prior training schedule. Data were collected before week three (T1), after week three (T2) and after a week of recovery by training cessation (T3). During week three, SUP consumed an amino acid, carbohydrate and creatine monohydrate containing recovery drink immediately after each training bout. PL was provided a drink of similar appearance and taste but containing minimal nutritional value. At T2, both SUP and PL decreased mean squat velocity and power at 70% 1RM. Additionally, SUP and PL decreased muscle β₂-adrenergic receptor (β₂-AR) expression by 61 and 83%, respectively. Increases in the ratio of nocturnal urinary epinephrine/β₂-AR ratio (EPI: β₂AR) for SUP and PL suggested impaired sympathetic nervous system sensitivity. SUP demonstrated a smaller decrease in β₂-AR expression and a lower EPI: β₂AR, suggesting the recovery drink attenuated the detrimental effects of overreaching on the sympathetic activity. In conclusion, high power resistance exercise overreaching can induce performance decrements and impair sympathetic activity, but these effects may be attenuated by supplementation.     

Can species‐specific prey responses to chemical cues explain prey susceptibility to predation?

The perception of danger represents an essential ability of prey for gaining an informational advantage over their natural enemies. Especially in complex environments or at night, animals strongly rely on chemoreception to avoid predators. The ability to recognize danger by chemical cues and subsequent adaptive responses to predation threats should generally increase prey survival. Recent findings suggest that European catfish (Silurus glanis) introduction induce changes in fish community and we tested whether the direction of change can be attributed to differences in chemical cue perception. We tested behavioral response to chemical cues using three species of freshwater fish common in European water: rudd (Scardinius erythrophthalmus), roach (Rutilus rutilus), and perch (Perca fluviatilis). Further, we conducted a prey selectivity experiment to evaluate the prey preferences of the European catfish. Roach exhibited the strongest reaction to chemical cues, rudd decreased use of refuge and perch did not alter any behavior in the experiment. These findings suggest that chemical cue perception might be behind community data change and we encourage collecting more community data of tested prey species before and after European catfish introduction to test the hypothesis. We conclude that used prey species can be used as a model species to verify whether chemical cue perception enhances prey survival.