Acetate assimilation by Nitrobacter agilis in relation to its "obligate autotrophy"

Acetate (1 to 10 mm) had no effect on the rate of nitrite oxidation or exponential growth by Nitrobacter agilis. However, acetate-1-(14)C and -2-(14)C were both assimilated by growing cultures, and acetate carbon contributed 33 to 39% of newly synthesized cell carbon. Carbon from acetate was incorporated into all of the major cell constituents, including most of the amino acids of cell protein and poly-beta-hydroxybutyrate (PHB). Cultures grown in the presence of acetate showed a significant increase in turbidity, attributable in part to protein synthesis and the accumulation of PHB in the "post-exponential phase," when the supply of nitrite was completely exhausted. Cell suspensons of N. agilis assimilated acetate in the absence of bicarbonate and even in the absence of nitrite. However, the addition of nitrite increased the rate of acetate assimilation by cell suspensions. The distribution of (14)C-acetate incorporated by cell suspensions was qualitatively similar to that found with growing cultures. Cell suspensions of N. agilis slowly oxidized acetate to CO(2). Addition of nitrite suppressed CO(2) production from acetate but increased the assimilation of acetate carbon into cell material. N. agilis contained all the enzymes of the tricarboxylic acid cycle. Growth of N. agilis in the presence of acetate did not significantly affect the levels of the enzymes of the tricarboxylic acid cycle, but did result in a 100-fold increase in the specific activity of isocitratase. In contrast, carboxydismutase was partially repressed. N. agilis was grown heterotrophically through seven transfers on a medium containing acetate and casein hydrolysate. The addition of nitrite increased the rate of heterotrophic growth. Heterotrophically grown organisms still retained their ability to grow autotrophically with nitrite. However, these organisms oxidized nitrite at a slower rate. Organisms from autotrophic and heterotrophic cultures were analyzed to determine the mean guanine plus cytosine content of their deoxyribonucleic acid; in both cases this mean was 61.2 +/- 1%. We concluded that N. agilis is not an obligate autotroph; it appears to be a facultative autotroph which resembles the novel facultative autotroph, Thiobacillus intermedius, very closely.     

Insect economic levels in relation to crop production

Levels of economic insect damage and their effects on crop production are the most often-discussed issue in insect management today. The economic injury level (EIL) concept is the base for decision-making in most integrated pest management (IPM) programs. IPM programs are fundamentally different from control approaches that handle insect problems by focusing on tolerating insect effects. EIL is essential for IPM programs as it indicates which levels of insect populations can be tolerated and which cannot. By increasing our ability to tolerate insects, it is possible to eliminate or reduce the need for management tactics. Scientists can maintain environmental quality through better decisions on the use of those tactics. EILs help maintain environmental quality by reducing unnecessary use of management tactics, especially insecticides. However, including environmental considerations explicitly in the decision-making process could greatly improve the ability of IPM to sustain environmental quality. The EIL components include economic damage, economic thresholds, and the EIL itself. Increased availability of calculated EILs and their related economic thresholds would reduce unnecessary use of management tactics. An environmental EIL evaluates a management tactic based not only on its direct costs and benefits to the user but also on its effects on the environment. There are many factors that can reduce crop yield. One important cause is insects. Insects that cause loss to the fruits are frequently more destructive than those that damage leaves, stems and roots. For example, cotton is infested by Spodoptera littoralis (Boisd.), Pectinophora gossypiella (Saund.), Helicoverpa armigera (Hün.) and Earias insulana (Boisd.) cause the greatest yield losses. The amount of yield loss is dependent upon a number of factors, i.e., plant variety, soil fertility, insect population and skill in handling crop production, etc. Comparatively tolerant varieties, even at the cost of slightly less yield potential, will be more suitable under such conditions.     

In vitro activity of a new glycopeptide antibiotic eremomycin in relation to obligate anaerobic Gram-positive bacteria]

Antibacterial activity of eremomycin, a novel glycopeptide antibiotic, against obligate anaerobic Gram-positive++ bacteria was studied. Eremomycin was shown to inhibit the growth of obligate anaerobic Gram-positive++ cocci and bacteria belonging to Clostridium in rather low concentrations and within narrow ranges of the MIC which was indicative of the antibiotic undoubted advantages. The antibacterial activity of eremomycin was 2 times as high as that of vancomycin and 8 times as high as that of ristomycin with respect to Gram-positive++ anaerobic cocci. Pathogenic strains of Clostridium spp. were 2 to 4 times more sensitive to eremomycin than to vancomycin. A significant property of the novel glycopeptide antibiotic was shown to be its capacity for inhibiting the growth of Gram-positive++ aerobic and obligate anaerobic cocci within the same concentration ranges which might be of importance in monotherapy of mixed aerobic and anaerobic infections.     

Relationship between phototrophy and phagotrophy in the mixotrophic chrysophytePoterioochromonas malhamensis

The time scales involved in the transition between phototrophic and phagotrophic modes of nutrition were examined in the mixotrophic chrysophytePoterioochromonas malhamensis. Phagotrophy began almost immediately when bacteria were added to phototrophically growing cultures of the alga, and chlorophylla concentration per cell in these cultures decreased over a 24-hour period. Chlorophyll concentrations per cell began to increase when bacteria were grazed to a density of approximately 10⁶ ml^–1, but after more than 24 hours they had not returned to the higher chlorophyll concentrations observed in the phototrophically grown cultures. Bacterivory was the dominant mode of nutrition in all cultures containing heat-killed bacteria. Photosynthesis did not contribute more than 7% of the total carbon budget of the alga when in the presence of abundant heat-killed bacteria. Bacterial density was the primary factor influencing the ability ofP. malhamensis to feed phagotrophically, while light intensity, pH, and the presence of dissolved organic matter had no effect on phagotrophy. We conclude thatP. malhamensis is capable of phagotrophy at all times. In contrast, phototrophy is inducible in the light during starvation and is a long-term survival strategy for this mixotrophic alga (i.e., it operates on time scales greater than a diel cycle).     

Temperature‐dependent phagotrophy and phototrophy in a mixotrophic chrysophyte

The roles of temperature and light on grazing and photosynthesis were examined for Dinobryon sociale, a common freshwater mixotrophic alga. Photosynthetic rate was determined for D. sociale adapted to temperatures of 8, 12, 16, and 20°C under photosynthetically active radiation light irradiances of 25, 66, and 130 μmol photons · m^?2 · s^?1, with concurrent measurement of bacterial ingestion at all temperatures under medium and high light (66 and 130 μmol photons · m^?2 · s^?1). Rates of ingestion and photosynthesis increased with temperature to a maximum at 16°C under the two higher light regimes, and declined at 20°C. Although both light and temperature had a marked effect on photosynthesis, there was no significant difference in bacterivory at medium and high irradiances at any given temperature. At the lowest light condition (25 μmol photons · m^?2 · s^?1), photosynthesis remained low and relatively stable at all temperatures. D. sociale acquired the majority of carbon from photosynthesis, although the low photosynthetic rate without a concurrent decline in feeding rate at 8°C suggested 20%–30% of the carbon budget could be attributed to bacterivory at low temperatures. Grazing experiments in nutrient‐modified media revealed that this mixotroph had increased ingestion rates when either dissolved nitrogen or phosphorus was decreased. This work increases our understanding of environmental effects on mixotrophic nutrition. Although the influence of abiotic factors on phagotrophy and phototrophy in pure heterotrophs and phototrophs has been well studied, much less is known for mixotrophic organisms.     

Plasma BDNF levels vary in relation to body weight in females

Brain derived neurotrophic factor (BDNF) has been implicated in the pathophysiology of depression as well as neuropsychiatric and neurodegenerative disorders. Recent studies show a role of BDNF in energy metabolism and body weight regulation. We examined BDNF levels in plasma and cerebrospinal fluid (CSF) samples from age matched elderly depressed and control subjects. Also, the association of BDNF levels with age, gender, body weight, body mass index (BMI), and cognitive performance was evaluated. We did not find any significant differences in plasma and CSF BDNF levels between depressed and control subjects. Plasma BDNF levels were negatively correlated with age (but not with BMI and body weight), when analyses were performed including both depressed and control subjects. A significant reduction in plasma BDNF levels was observed in females as compared to male subjects, and the change in BDNF levels were significantly and positively related to body weight in females. Furthermore, significant increases in Total Recall and Delayed Recall values were found in females as compared to males. In conclusion, the lower BDNF levels observed in females suggest that changes in peripheral BDNF levels are likely secondary to an altered energy balance. However, further studies using larger sample size are warranted.     

Iron-manganese interaction and its relation to boron levels in tomato plants

Plant and Soil - Using a factorial design with deficient to toxic levels of Mn and B, the absorption and distribution of Fe in tomato plants (Lycopersicum esculentum, var. Marglobe), grown...     

Changes in cellular glutathione levels: possible relation to selenium-mediated anticarcinogenesis

Mechanisms of Se-mediated anticarcinogenesis were investigated. Excess Se as Na2SeO3 reversibly decreased mammalian cell proliferation in vitro. This inhibitory effect was exerted primarily in G1 of the cell cycle; however, S and G2 were also affected. Cellular glutathione concentrations both in vitro and in vivo were altered by excess Se administration. These results are discussed in terms of altered cellular glutathione metabolism and its possible implications for cell proliferation.     

Thermal adaptation in yeast: obligate psychrophiles are obligate aerobes, and obligate thermophiles are facultative anaerobes.

The obligate psychrophilic yeasts Torulopsis psychrophila, T. austromarina, Leucosporidium frigidum, L. gelidum, and L. nivalis were obligate aerobes and were unable to grow anaerobically. In contrast, the obligate thermophilic yeasts T. bovina, T. pintolopesii, Candida slooffii, and Saccharomyces telluris were facultative anaerobes.     

The evolutionary pathway to obligate scavenging in Gyps vultures

The evolutionary pathway to obligate scavenging in Gyps vultures remains unclear. We propose that communal roosting plays a central role in setting up the information transfer network critical for obligate scavengers in ephemeral environments and that the formation of a flotilla-like foraging group is a likely strategy for foraging Gyps vultures. Using a spatial, individual-based, optimisation model we find that the communal roost is critical for establishing the information network that enables information transfer owing to the spatial-concentration of foragers close to the roost. There is also strong selection pressure for grouping behaviour owing to the importance of maintaining network integrity and hence information transfer during foraging. We present a simple mechanism for grouping, common in many animal species, which has the added implication that it negates the requirement for roost-centric information transfer. The formation of a flotilla-like foraging group also improves foraging efficiency through the reduction of overlapping search paths. Finally, we highlight the importance of consideration of information transfer mechanisms in order to maximise the success of vulture reintroduction programmes.