Corals shed bacteria as a potential mechanism of resilience to organic matter enrichment

Understanding the mechanisms of resilience of coral reefs to anthropogenic stressors is a critical step toward mitigating their current global decline. Coral–bacteria associations are fundamental to reef health and disease, but direct observations of these interactions remain largely unexplored. Here, we use novel technology, high-speed laser scanning confocal microscopy on live coral (Pocillopora damicornis), to test the hypothesis that corals exert control over the abundance of their associated bacterial communities by releasing (‘shedding'') bacteria from their surface, and that this mechanism can counteract bacterial growth stimulated by organic inputs. We also test the hypothesis that the coral pathogen Vibrio coralliilyticus can evade such a defense mechanism. This first report of direct observation with high-speed confocal microscopy of living coral and its associated bacterial community revealed a layer (3.3–146.8 μm thick) on the coral surface where bacteria were concentrated. The results of two independent experiments showed that the bacterial abundance in this layer was not sensitive to enrichment (5 mg l⁻¹ peptone), and that coral fragments exposed to enrichment released significantly more bacteria from their surfaces than control corals (P<0.01; 35.9±1.4 × 10⁵ cells cm⁻² coral versus 1.3±0.5 × 10⁵ cells cm⁻² coral). Our results provide direct support to the hypothesis that shedding bacteria may be an important mechanism by which coral-associated bacterial abundances are regulated under organic matter stress. Additionally, the novel ability to watch this ecological behavior in real-time at the microscale opens an unexplored avenue for mechanistic studies of coral–microbe interactions.     

Inactivation of Poliovirus 1 and F-Specific RNA Phages and Degradation of Their Genomes by UV Irradiation at 254 Nanometers

Several models (animal caliciviruses, poliovirus 1 [PV1], and F-specific RNA bacteriophages) are usually used to predict inactivation of nonculturable viruses. For the same UV fluence, viral inactivation observed in the literature varies from 0 to 5 logs according to the models and the methods (infectivity versus molecular biology). The lack of knowledge concerning the mechanisms of inactivation due to UV prevents us from selecting the best model. In this context, determining if viral genome degradation may explain the loss of infectivity under UV radiation becomes essential. Thus, four virus models (PV1 and three F-specific RNA phages: MS2, GA, and Qβ) were exposed to UV radiation from 0 to 150 mJ · cm⁻². PV1 is the least-resistant virus, while MS2 and GA phages are the most resistant, with phage Qβ having an intermediate sensitivity; respectively, 6-log, 2.3-log, 2.5-log, and 4-log decreases for 50 mJ · cm⁻². In parallel, analysis of RNA degradation demonstrated that this phenomenon depends on the fragment size for PV1 as well as for MS2. Long fragments (above 2,000 bases) for PV1 and MS2 fell rapidly to the background level (>1.3-log decrease) for 20 mJ · cm⁻² and 60 mJ · cm^{− 2}, respectively. Nevertheless, the size of the viral RNA is not the only factor affecting UV-induced RNA degradation, since viral RNA was more rapidly degraded in PV1 than in the MS2 phage with a similar size. Finally, extrapolation of inactivation and UV-induced RNA degradation kinetics highlights that genome degradation could fully explain UV-induced viral inactivation.     

Sediment Nitrification, Denitrification, and Nitrous Oxide Production in a Deep Arctic Lake

We used a combination of ¹⁵N tracer methods and a C₂H₂ blockage technique to determine the role of sediment nitrification and denitrification in a deep oligotrophic arctic lake. Inorganic nitrogen concentrations ranged between 40 and 600 nmol · cm⁻³, increasing with depth below the sediment-water interface. Nitrate concentrations were at least 10 times lower, and nitrate was only detectable within the top 0 to 6 cm of sediment. Eh and pH profiles showed an oxidized surface zone underlain by more reduced conditions. The lake water never became anoxic. Sediment Eh values ranged from −7 to 484 mV, decreasing with depth, whereas pH ranged from 6.0 to 7.3, usually increasing with depth. The average nitrification rate (49 ng of N · cm⁻³ · day⁻¹) was similar to the average denitrification rate (44 ng of N · cm⁻³ · day⁻¹). In situ N₂O production from nitrification and denitrification ranged from 0 to 25 ng of N · cm⁻³ · day⁻¹. Denitrification appears to depend on the supply of nitrate by nitrification, such that the two processes are coupled functionally in this sediment system. However, the low rates result in only a small nitrogen loss.     

Microbial Consumption of Atmospheric Isoprene in a Temperate Forest Soil

Isoprene (2-methyl-1,3 butadiene) is a low-molecular-weight hydrocarbon emitted in large quantities to the atmosphere by vegetation and plays a large role in regulating atmospheric chemistry. Until now, the atmosphere has been considered the only significant sink for isoprene. However, in this study we performed both in situ and in vitro experiments with soil from a temperate forest near Ithaca, N.Y., that indicate that the soil provides a sink for atmospheric isoprene and that the consumption of isoprene is carried out by microorganisms. Consumption occurred rapidly in field chambers (672.60 ± 30.12 to 2,718.36 ± 86.40 pmol gdw⁻¹ day⁻¹) (gdw is grams [dry weight] of soil; values are means ± standard deviations). Subsequent laboratory experiments confirmed that isoprene loss was due to biological processes: consumption was stopped by autoclaving the soil; consumption rates increased with repeated exposure to isoprene; and consumption showed a temperature response consistent with biological activity (with an optimum temperature of 30°C). Isoprene consumption was diminished under low oxygen conditions (120 ± 7.44 versus 528.36 ± 7.68 pmol gdw⁻¹ day⁻¹ under ambient O₂ concentrations) and showed a strong relationship with soil moisture. Isoprene-degrading microorganisms were isolated from the site, and abundance was calculated as 5.8 × 10⁵ ± 3.2 × 10⁵ cells gdw⁻¹. Our results indicate that soil may provide a significant biological sink for atmospheric isoprene.     

Quantification of Left Ventricular Torsion and Diastolic Recoil Using Cardiovascular Magnetic Resonance Myocardial Feature Tracking

Objectives

Cardiovascular magnetic resonance feature tracking (CMR-FT) offers quantification of myocardial deformation from routine cine images. However, data using CMR-FT to quantify left ventricular (LV) torsion and diastolic recoil are not yet available. We therefore sought to evaluate the feasibility and reproducibility of CMR-FT to quantify LV torsion and peak recoil rate using an optimal anatomical approach.

Methods

Short-axis cine stacks were acquired at rest and during dobutamine stimulation (10 and 20 µg·kg⁻¹·min⁻¹) in 10 healthy volunteers. Rotational displacement was analysed for all slices. A complete 3D-LV rotational model was developed using linear interpolation between adjacent slices. Torsion was defined as the difference between apical and basal rotation, divided by slice distance. Depending on the distance between the most apical (defined as 0% LV distance) and basal (defined as 100% LV distance) slices, four different models for the calculation of torsion were examined: Model-1 (25–75%), Model-2 (0–100%), Model-3 (25–100%) and Model-4 (0–75%). Analysis included subendocardial, subepicardial and global torsion and recoil rate (mean of subendocardial and subepicardial values).

Results

Quantification of torsion and recoil rate was feasible in all subjects. There was no significant difference between the different models at rest. However, only Model-1 (25–75%) discriminated between rest and stress (Global Torsion: 2.7±1.5°cm⁻¹, 3.6±2.0°cm⁻¹, 5.1±2.2°cm⁻¹, p<0.01; Global Recoil Rate: −30.1±11.1°cm⁻¹s⁻¹,−46.9±15.0°cm⁻¹s⁻¹,−68.9±32.3°cm⁻¹s⁻¹, p<0.01; for rest, 10 and 20 µg·kg⁻¹·min⁻¹ of dobutamine, respectively). Reproducibility was sufficient for all parameters as determined by Bland-Altman analysis, intraclass correlation coefficients and coefficient of variation.

Conclusions

CMR-FT based derivation of myocardial torsion and recoil rate is feasible and reproducible at rest and with dobutamine stress. Using an optimal anatomical approach measuring rotation at 25% and 75% apical and basal LV locations allows effective quantification of torsion and recoil dynamics. Application of these new measures of deformation by CMR-FT should next be explored in disease states.     

Attachment of and Biofilm Formation by Enterobacter sakazakii on Stainless Steel and Enteral Feeding Tubes

Enterobacter sakazakii has been reported to form biofilms, but environmental conditions affecting attachment to and biofilm formation on abiotic surfaces have not been described. We did a study to determine the effects of temperature and nutrient availability on attachment and biofilm formation by E. sakazakii on stainless steel and enteral feeding tubes. Five strains grown to stationary phase in tryptic soy broth (TSB), infant formula broth (IFB), or lettuce juice broth (LJB) at 12 and 25°C were examined for the extent to which they attach to these materials. Higher populations attached at 25°C than at 12°C. Stainless steel coupons and enteral feeding tubes were immersed for 24 h at 4°C in phosphate-buffered saline suspensions (7 log CFU/ml) to facilitate the attachment of 5.33 to 5.51 and 5.03 to 5.12 log CFU/cm², respectively, before they were immersed in TSB, IFB, or LJB, followed by incubation at 12 or 25°C for up to 10 days. Biofilms were not produced at 12°C. The number of cells of test strains increased by 1.42 to 1.67 log CFU/cm² and 1.16 to 1.31 log CFU/cm² in biofilms formed on stainless steel and feeding tubes, respectively, immersed in IFB at 25°C; biofilms were not formed on TSB and LJB at 25°C, indicating that nutrient availability plays a major role in processes leading to biofilm formation on the surfaces of these inert materials. These observations emphasize the importance of temperature control in reconstituted infant formula preparation and storage areas in preventing attachment and biofilm formation by E. sakazakii.     

Detection of UV-Induced Thymine Dimers in Individual Cryptosporidium parvum and Cryptosporidium hominis Oocysts by Immunofluorescence Microscopy

To investigate the effect of UV light on Cryptosporidium parvum and Cryptosporidium hominis oocysts in vitro, we exposed intact oocysts to 4-, 10-, 20-, and 40-mJ·cm⁻² doses of UV irradiation. Thymine dimers were detected by immunofluorescence microscopy using a monoclonal antibody against cyclobutyl thymine dimers (anti-TDmAb). Dimer-specific fluorescence within sporozoite nuclei was confirmed by colocalization with the nuclear fluorogen 4′,6′-diamidino-2-phenylindole (DAPI). Oocyst walls were visualized using either commercial fluorescein isothiocyanate-labeled anti-Cryptosporidium oocyst antibodies (FITC-CmAb) or Texas Red-labeled anti-Cryptosporidium oocyst antibodies (TR-CmAb). The use of FITC-CmAb interfered with TD detection at doses below 40 mJ·cm⁻². With the combination of anti-TDmAb, TR-CmAb, and DAPI, dimer-specific fluorescence was detected in sporozoite nuclei within oocysts exposed to 10 to 40 mJ·cm⁻² of UV light. Similar results were obtained with C. hominis. C. parvum oocysts exposed to 10 to 40 mJ·cm⁻² of UV light failed to infect neonatal mice, confirming that results of our anti-TD immunofluorescence assay paralleled the outcomes of our neonatal mouse infectivity assay. These results suggest that our immunofluorescence assay is suitable for detecting DNA damage in C. parvum and C. hominis oocysts induced following exposure to UV light.     

Inhibition of glucose phosphate isomerase by metabolic intermediates of fructose

1. Purified rabbit-muscle and -liver glucose phosphate isomerase, free of contaminating enzyme activities that could interfere with the assay procedures, were tested for inhibition by fructose, fructose 1-phosphate and fructose 1,6-diphosphate. 2. Fructose 1-phosphate and fructose 1,6-diphosphate are both competitive with fructose 6-phosphate in the enzymic reaction, the apparent K_i values being 1·37×10⁻³−1·67×10⁻³m for fructose 1-phosphate and 7·2×10⁻³−7·9×10⁻³m for fructose 1,6-diphosphate; fructose and inorganic phosphate were without effect. 3. The apparent K_m values for both liver and muscle enzymes at pH7·4 and 30° were 1·11×10⁻⁴−1·29×10⁻⁴m for fructose 6-phosphate, determined under the conditions in this paper. 4. In the reverse reaction, fructose, fructose 1-phosphate and fructose 1,6-diphosphate did not significantly inhibit the conversion of glucose 6-phosphate into fructose 6-phosphate. 5. The apparent K_m values for glucose 6-phosphate were in the range 5·6×10⁻⁴−8·5×10⁻⁴m. 6. The competitive inhibition of hepatic glucose phosphate isomerase by fructose 1-phosphate is discussed in relation to the mechanism of fructose-induced hypoglycaemia in hereditary fructose intolerance.     

Factors Influencing the Induction of Freezing Tolerance by Abscisic Acid in Cell Suspension Cultures of Bromus inermis Leyss and Medicago sativa L

A 2-gram fresh weight inoculum of bromegrass (Bromus inermis Leyss. culture BG970) cell suspension culture treated with 7.5 × 10⁻⁵ molar abscisic acid (ABA) for 7 days at 25°C survived slow cooling to −60°C. Over 80% of the cells in ABA treated cultures survived immersion in liquid N₂ after slow cooling to −40 or −60°C. In contrast, a 6-gram fresh weight inoculum only attained a hardiness level of −28°C after 5 days of ABA treatment. Ethanol (2 × 10⁻² molar) added to the culture medium at the time of ABA addition, inhibited the freezing tolerance of bromegrass cells by 25°C. A 6-gram inoculum of both control and ABA treated bromegrass cells altered the pH of the medium more than a 2-gram inoculum. ABA inhibited the increase in fresh weight of bromegrass by 20% after 4 days. Both control and ABA (10⁻⁴ molar) treated alfalfa cells (Medicago sativa L.) grown at 25°C hardened from an initial LT₅₀ of −5°C to an LT₅₀ of −23°C by the third to fifth day after subculture. Thereafter, the cells dehardened but the ABA treated cells did not deharden to the same level as the control cells. ABA inhibited the increase in fresh weight of alfalfa by 50% after 5 days.     

Effects of Light, Carbon Dioxide, and Temperature on Photosynthesis, Oxygen Inhibition of Photosynthesis, and Transpiration in Solanum tuberosum

Individual leaves of potato (Solanum tuberosum L. W729R), a C₃ plant, were subjected to various irradiances (400-700 nm), CO₂ levels, and temperatures in a controlled-environment chamber. As irradiance increased, stomatal and mesophyll resistance exerted a strong and some-what paralleled regulation of photosynthesis as both showed a similar decrease reaching a minimum at about 85 neinsteins·cm⁻²·sec⁻¹ (about ½ of full sunlight). Also, there was a proportional hyperbolic increase in transpiration and photosynthesis with increasing irradiance up to 85 neinsteins·cm⁻²·sec⁻¹. These results contrast with many C₃ plants that have a near full opening of stomata at much less light than is required for saturation of photosynthesis.     

Biofilm formation on brass coupons exposed to a cooling system of an oil refinery

Brass coupons (70% Cu 30% Zn) were exposed to a cooling freshwater system of an oil refinery, in order to investigate susceptibility of the metal to biofilm formation. The coupons were fixed on bypasses at points which allowed the circulation of makeup, cooling and return water. The number of aerobic, anaerobic and sulfate-reducing bacteria was determined in both the planktonic and the sessile phases. Maximum bacterial concentrations were detected in the cooling water, corresponding to 2.1 ± 0.1 × 10⁶ CFU ml⁻¹ (planktonic phase) and 1.3 ± 0.2 × 10⁵ CFU cm⁻² (sessile phase) for aerobic bacteria and to 3.2 ± 0.3 × 10⁵ cells ml⁻¹ (planktonic phase) and 6.2 ± 0.7 × 10⁵ cells cm⁻² (sessile phase) for anaerobic bacteria. Sulfate-reducing bacteria (SRB) were observed only in the planktonic phase, being found in greater numbers in the return water. Scanning electron microscopy (SEM) analysis indicated that biofilm formation occurred at the three monitored sites and showed a diversity in cell morphology. Nonetheless, no evidence of corrosion was observed on the brass coupons during the experimental period. Received 22 May 1997/ Accepted in revised form 19 September 1997     

Wildland fire as an atmospheric source of viable microbial aerosols and biological ice nucleating particles

The environmental sources of microbial aerosols and processes by which they are emitted into the atmosphere are not well characterized. In this study we analyzed microbial cells and biological ice nucleating particles (INPs) in smoke emitted from eight prescribed wildland fires in North Florida. When compared to air sampled prior to ignition, samples of the air–smoke mixtures contained fivefold higher concentrations of microbial cells (6.7 ± 1.3 × 10⁴ cells m⁻³) and biological INPs (2.4 ± 0.91 × 10³ INPs m⁻³ active at temperatures ≥ −15 °C), and these data significantly positively correlated with PM₁₀. Various bacteria could be cultured from the smoke samples, and the nearest neighbors of many of the isolates are plant epi- and endophytes, suggesting vegetation was a source. Controlled laboratory combustion experiments indicated that smoke emitted from dead vegetation contained significantly higher numbers of cells, INPs, and culturable bacteria relative to the green shrubs tested. Microbial viability of smoke aerosols based on formazan production and epifluorescent microscopy revealed no significant difference in the viable fraction (~80%) when compared to samples of ambient air. From these data, we estimate each fire aerosolized an average of 7 ± 4 × 10⁹ cells and 2 ± 1 × 10⁸ biological INPs per m² burned and conclude that emissions from wildland fire are sources of viable microbial aerosols to the atmosphere.Subject terms: Air microbiology, Microbial ecology, Microbial ecology, Forest ecology     

Steady-State Effects of 2,5,2′,5′-Tetrachlorobiphenyl on Growth, Photosynthesis, and P Uptake in Selenastrum capricornutum

The steady-state effect of 2,5,2′,5′-tetrachlorobiphenyl (TCBP) on the green alga Selenastrum capricornutum was investigated in a P-limited two-stage chemostat system. The partition coefficient of this polychlorinated biphenyl congener was 5.9 × 10⁴ in steady-state cultures. At a cellular TCBP concentration of 12.2 × 10⁻⁸ ng · cell⁻¹, growth rate was not affected. However, photosynthetic capacity (P_max) was significantly enhanced by TCBP (56 × 10⁻⁹ μmol of C · cell⁻¹ · h⁻¹ versus 34 × 10⁻⁹ μmol of C · cell⁻¹ · h⁻¹ in the control). Photosynthetic efficiency, or the slope of the photosynthesis-irradiance curve, was also significantly higher. There was little difference in the cell chlorophyll a content, and therefore the difference in these photosynthetic characteristics was the same even when they were expressed on a per-chlorophyll a basis. Cell C content was higher in TCBP-containing cells than in TCBP-free cells, but approximately 36% of the C fixed by cells with TCBP was not incorporated as cell C. The maximum P uptake rate was also enhanced by TCBP, but the half-saturation concentration appeared to be unaffected.     

Proteins of ruminant colostrum

1. The proteins in the whey of ewe colostrum resemble those obtained from goat colostrum in containing two main electrophoretic components, with mobilities of −2×10⁻⁵ and −3·9×10⁻⁵ cm.²sec.⁻¹v⁻¹ in sodium veronal buffer, pH 8·6 and I 0·1, at 1°. 2. Of 32 samples of goat colostrum examined by paper electrophoresis 27 contained the immune lactoglobulin characteristic of colostrum; of 55 samples of cow colostrum all contained immune lactoglobulin.     

Proteinuria of newborn suckling ruminants

1. The proteins in the whey of ewe colostrum resemble those obtained from goat colostrum in containing two main electrophoretic components, with mobilities of −2×10⁻⁵ and −3·9×10⁻⁵ cm.²sec.⁻¹v⁻¹ in sodium veronal buffer, pH 8·6 and I 0·1, at 1°. 2. Of 32 samples of goat colostrum examined by paper electrophoresis 27 contained the immune lactoglobulin characteristic of colostrum; of 55 samples of cow colostrum all contained immune lactoglobulin.     

Rotating Magnetic Field-Assisted Reactor Enhances Mechanisms of Phage Adsorption on Bacterial Cell Surface

Growing interest in bacteriophage research and use, especially as an alternative treatment option for multidrug-resistant bacterial infection, requires rapid development of production methods and strengthening of bacteriophage activities. Bacteriophage adsorption to host cells initiates the process of infection. The rotating magnetic field (RMF) is a promising biotechnological method for process intensification, especially for the intensification of micromixing and mass transfer. This study evaluates the use of RMF to enhance the infection process by influencing bacteriophage adsorption rate. The RMF exposition decreased the t₅₀ and t₇₅ of bacteriophages T4 on Escherichia coli cells and vb_SauM_A phages on Staphylococcus aureus cells. The T4 phage adsorption rate increased from 3.13 × 10⁻⁹ mL × min⁻¹ to 1.64 × 10⁻⁸ mL × min⁻¹. The adsorption rate of vb_SauM_A phages exposed to RMF increased from 4.94 × 10⁻⁹ mL × min⁻¹ to 7.34 × 10⁻⁹ mL × min⁻¹. Additionally, the phage T4 zeta potential changed under RMF from −11.1 ± 0.49 mV to −7.66 ± 0.29 for unexposed and RMF-exposed bacteriophages, respectively.     

Design and green synthesis of novel quinolinone derivatives of potential anti-breast cancer activity against MCF-7 cell line targeting multi-receptor tyrosine kinases

A new set of 4,6,7,8-tetrahydroquinolin-5(1H)-ones were designed as cytotoxic agents against breast cancer cell line (MCF-7) and synthesised under ultrasonic irradiation using chitosan decorated copper nanoparticles (CS/CuNPs) catalyst. The new compounds 4b, 4j, 4k, and 4e exhibited the most potent cytotoxic activity of IC₅₀ values (0.002 − 0.004 µM) comparing to Staurosporine of IC₅₀; 0.005 μM. The latter derivatives exhibited a promising safety profile against the normal human WI38 cells of IC₅₀ range 0.0149 − 0.048 µM. Furthermore, the most promising cytotoxic compounds 4b, 4j were evaluated as multi-targeting agents against the RTK protein kinases; EGFR, HER-2, PDGFR-β, and VEGFR-2. Compound 4j showed promising inhibitory activity against HER-2 and PDGFR-β of IC₅₀ values 0.17 × 10⁻³, 0.07 × 10⁻³ µM in comparison with the reference drug sorafenib of IC₅₀; 0.28 × 10⁻³, 0.13 × 10⁻³ µM, respectively. In addition, 4j induced apoptotic effect and cell cycle arrest at G2/M phase preventing the mitotic cycle in MCF-7 cells.     

Structure-Activity Relationships in Microbial Transformation of Phenols

The second-order rate constants for the microbial transformation of a series of phenols were correlated with the physicochemical properties of the phenols. The compounds studied were phenol, p-methylphenol, p-chlorophenol, p-bromophenol, p-cyanophenol, p-nitrophenol, p-acetylphenol, and p-methoxyphenol. Phenol-grown cells of Pseudomonas putida U transformed these compounds. Microbial transformation rate constants ranged from (1.5 ± 0.99) × 10⁻¹⁴ liter · organism⁻¹ · h⁻¹ for p-cyanophenol to (7.0 ± 1.3) × 10⁻¹² liter · organism⁻¹ · h⁻¹ for phenol. Linear regression analyses of rate constants and electronic, steric, and hydrophobic parameters showed that van der Waal's radii gave the best coefficient of determination (r² = 0.956). Products identified by thin-layer chromatography and liquid chromatography indicated that the phenols were microbially oxidized to the corresponding catechols.     

Mitochondrial Networks in Cardiac Myocytes Reveal Dynamic Coupling Behavior

Oscillatory behavior of mitochondrial inner membrane potential (ΔΨ_m) is commonly observed in cells subjected to oxidative or metabolic stress. In cardiac myocytes, the activation of inner membrane pores by reactive oxygen species (ROS) is a major factor mediating intermitochondrial coupling, and ROS-induced ROS release has been shown to underlie propagated waves of ΔΨ_m depolarization as well as synchronized limit cycle oscillations of ΔΨ_m in the network. The functional impact of ΔΨ_m instability on cardiac electrophysiology, Ca²⁺ handling, and even cell survival, is strongly affected by the extent of such intermitochondrial coupling. Here, we employ a recently developed wavelet-based analytical approach to examine how different substrates affect mitochondrial coupling in cardiac cells, and we also determine the oscillatory coupling properties of mitochondria in ventricular cells in intact perfused hearts. The results show that the frequency of ΔΨ_m oscillations varies inversely with the size of the oscillating mitochondrial cluster, and depends on the strength of local intermitochondrial coupling. Time-varying coupling constants could be quantitatively determined by applying a stochastic phase model based on extension of the well-known Kuramoto model for networks of coupled oscillators. Cluster size-frequency relationships varied with different substrates, as did mitochondrial coupling constants, which were significantly larger for glucose (7.78 × 10⁻² ± 0.98 × 10⁻² s⁻¹) and pyruvate (7.49 × 10⁻² ± 1.65 × 10⁻² s⁻¹) than lactate (4.83 × 10⁻² ± 1.25 × 10⁻² s⁻¹) or β-hydroxybutyrate (4.11 × 10⁻² ± 0.62 × 10⁻² s⁻¹). The findings indicate that mitochondrial spatiotemporal coupling and oscillatory behavior is influenced by substrate selection, perhaps through differing effects on ROS/redox balance. In particular, glucose-perfusion generates strong intermitochondrial coupling and temporal oscillatory stability. Pathological changes in specific catabolic pathways, which are known to occur during the progression of cardiovascular disease, could therefore contribute to altered sensitivity of the mitochondrial network to oxidative stress and emergent ΔΨ_m instability, ultimately scaling to produce organ level dysfunction.     

Dynamics of Microbial Communities on Marine Snow Aggregates: Colonization, Growth, Detachment, and Grazing Mortality of Attached Bacteria

We studied the dynamics of microbial communities attached to model aggregates (4-mm-diameter agar spheres) and the component processes of colonization, detachment, growth, and grazing mortality. Agar spheres incubated in raw seawater were rapidly colonized by bacteria, followed by flagellates and ciliates. Colonization can be described as a diffusion process, and encounter volume rates were estimated at about 0.01 and 0.1 cm³ h⁻¹ for bacteria and flagellates, respectively. After initial colonization, the abundances of flagellates and ciliates remained approximately constant at 10³ to 10⁴ and ~10² cells sphere⁻¹, respectively, whereas bacterial populations increased at a declining rate to >10⁷ cells sphere⁻¹. Attached microorganisms initially detached at high specific rates of ~10⁻² min⁻¹, but the bacteria gradually became irreversibly attached to the spheres. Bacterial growth (0 to 2 day⁻¹) was density dependent and declined hyperbolically when cell density exceeded a threshold. Bacterivorous flagellates grazed on the sphere surface at an average saturated rate of 15 bacteria flagellate⁻¹ h⁻¹. At low bacterial densities, the flagellate surface clearance rate was ~5 × 10⁻⁷ cm² min⁻¹, but it declined hyperbolically with increasing bacterial density. Using the experimentally estimated process rates and integrating the component processes in a simple model reproduces the main features of the observed microbial population dynamics. Differences between observed and predicted population dynamics suggest, however, that other factors, e.g., antagonistic interactions between bacteria, are of importance in shaping marine snow microbial communities.