Control Mechanisms Operative in a Natural Microbial Population Selected for Its Ability to Degrade L-Lysine. III. Effects of Carbohydrates in Continuous-Flow Systems Under Shock Load Conditions

Two naturally selected microbial populations were maintained under continuousflow conditions with glucose or magnesium growth-limiting. The reactors were subjected to shock loads by changing the influent substrate from L-lysine to a mixture of L-lysine and glucose, L-lysine and fructose, or L-lysine and ribose. During the subsequent transient state, the following parameters were examined: lysine chemical oxygen demand (COD), carbohydrate COD, total COD, biological solids concentration, cell protein, enzymatic capability (lysine-degrading enzymes), and the rate of lysine removal. The carbohydrate was then removed from the influent and the same parameters were examined until a new steady state was established. In all cases, glucose and fructose caused a significant repression of the synthesis of lysine-degrading enzymes, resulting in a decrease in the enzymatic capability of the cells. In the carbon-limited reactor, the faster the flow rate, the greater was the repression, whereas, in the magnesium-limited reactor, the slower the flow rate, the greater was the repression. The introduction of ribose into the reactors caused an initial increase in lysine enzymatic capability followed by a slight repression when ribose degradation started.     

Differential staining of calcified tissues in plastic embedded microtome sections by a modification of Movat's pentachrome stain.

Movat's pentachrome I stain has been adapted and modified as a stain for undecalcified bone sections. After embedding in methyl methacrylate, this procedure yields consistently good results, with an excellent and colorful contrast between mineralized and unmineralized compartments of both cartilage and bone. In addition, osteoblasts, osteoclasts, and other cells and tissue components can easily be differentiated. The staining properties of the lacunar wall surrounding the osteocytes are considered to reflect various states of osteocytic activity. The method is especially useful for the study of bone growth and bone repair, and as a stain for conventional histomorphometry and computer-assisted image analysis in bone biopsies.     

Experimental studies on a kinetic model for design and operation of activated sludge processes

Previous experimentation in our laboratory has shown that the classical theory developed for continuous growth of pure cultures in completely mixed aerobic systems in which the recycle cell concentration factor, c (where c = X_R/X), is a selectable system constant, did not provide a suitable model for the heterogeneous (natural) populations of the activated sludge process. Another model was derived in which the recycle cell concentration, X_R was employed as a system constant instead of c, and computational analysis was performed. Laboratory pilot plant experimentation was undertaken in order to determine whether a “steady state” in aerator biological solids concentration, X?, and substrate concentration, S?, could be approached under this mode of operation. Studies were performed at various organic feed concentrations holding dilution rate, D, at 0.125 hr^?1, hydraulic recycle ratio, α, at 0.25, and X^R at 10,000 mg/liter. Also, values of maximum specific growth rate, μ_max, and saturation constant, K_s were determined. It was found that the model approached the steady state condition with heterogeneous populations more closely than did the classical model, and the high degree of treatment efficiency predicted by the model was demonstrated experimentally.     

Variability in cell yield for heterogeneous microbial populations of sewage origin grown on glucose

Values of cell yield collected over a period of eight years for heterogeneous populations of sewage origin acclimated to glucose in both batch and continuous culture were subjected to statistical analysis. The cell yield for this sole source of carbon (glucose) ranged from 36 to 88 per cent in batch culture, and 32 to 69 per cent in continuous culture. Because experimental conditions were known and well defined, the variability in cell yield is attributable to the ecological variation inherent in a heterogeneous population. The data presented demonstrate the futility of attempts to define Y for such populations as a precise theoretical constant dependent upon thermodynamic properties of the substrate.     

Loss of Kupffer cells in diet-induced obesity is associated with increased hepatic steatosis,STAT3 signaling,and further decreases in insulin signaling

While adipose tissue-associated macrophages contribute to development of chronic inflammation and insulin resistance of obesity, little is known about the role of hepatic Kupffer cells in this environment. Here we address the impact of Kupffer cell ablation using clodronate-encapsulated liposome depletion in a diet-induced obese (DIO) and insulin resistant mouse model. Hepatic expression of macrophage markers measured by realtime RT-PCR remained unaltered in DIO mice despite characteristic expansion of adipose tissue-associated macrophages. DIO mouse livers displayed increased expression of alternative activation markers but unaltered proinflammatory cytokine expression when compared to lean mice. Kupffer cell ablation reduced hepatic anti-inflammatory cytokine IL-10 mRNA expression in lean and DIO mice by 95% and 84%, respectively. Despite decreased hepatic IL-6 gene expression after ablation in lean and DIO mice, hepatic STAT3 phosphorylation, Socs3 and acute phase protein mRNA expression increased. Kupffer cell ablation in DIO mice resulted in additional hepatic triglyceride accumulation and a 30–40% reduction in hepatic insulin receptor autophosphorylation and Akt activation. Implicating systemic loss of IL-10, high-fat-fed IL-10 knockout mice also displayed increased hepatic STAT3 signaling and hepatic triglyceride accumulation. Insulin signaling was not altered, however. In conclusion, Kupffer cells are a major source of hepatic IL-10 expression, the loss of which is associated with increased STAT3-dependent signaling and steatosis. One or more additional factors appear to be required, however, for the Kupffer cell-dependent protective effect on insulin receptor signaling in DIO mice.     

Factors Affecting Filamentous Growth of Sphaerotilus natans

Filamentous growth in cultures of Sphaerotilus natans can be measured and compared with total growth by a standardized procedure of winding filaments around an inoculating needle. Filaments and residual growth are then separately washed on Millipore filters, dried, and weighed. This method has been used to study changes in the growth habit of S. natans elicited by changes in the concentration of nutrients in the medium. The concentration of peptone, in a medium containing a sugar, phosphate buffer, and inorganic salts, has a much greater effect on the proportion of filamentous growth than does the nature or concentration of the carbon source or the concentration of phosphate buffer. Filament formation is significantly inhibited by concentrations of peptone greater than 0.25%; further increases in peptone concentration stimulate the production of large amounts of capsular material. Increasing the concentration of phosphate buffer to 0.05 M almost completely inhibits growth of S. natans.     

Use of Chemical Oxygen Demand Values of Bacterial Cells in Waste-Water Purification

Four methods for determining substrate recoveries in studies concerned with the partition of substrate between sludge synthesis and respiration were investigated. An energy balance comparing chemical oxygen demand (COD) removed with the summation of oxygen uptake and the COD of the cells produced yielded average recoveries closer to 100% than any of the other three methods tested. The standard COD test was shown to yield highly reproducible values when used to determine the COD of activated sludge. Although the protein and carbohydrate content of the cells varied with cell age, a concomitant variation in cell COD was not noted.