The Properties of a cellulolytic microbial community growing on pure cellulose and lignocellulose

A microbial community capable of degrading pure cellulose has been isolated from soil using a continuous flow chemostat. The component organisms have been identified as Penicillium nigricans, Paecilomyces liliacinus, Fusarium oxysporum (3 strains), Aspergillus fumigatus, Gliocladium roseum, and Penicillium simplicissimum. Extracellular enzyme production (exoglucanase, endoglucanase, and (Β-glucosidase) and cellulose breakdown by the whole community and the component organisms in pure culture was measured during growth on pure cellulose in batch culture. After 30 d, 50–60% degradation was achieved by Penicillium simplicissimum, Aspergillus fumigatus, and the mixed culture. These cultures also produced the highest levels of extracellular endo- and exoglucanase and were able to produce the full enzyme complex necessary for the degradation of crystalline cellulose. The other isolates were capable of 0–20% degradation and produced lower levels of enzyme activity. Most were unable to produce the full enzyme complex. The results indicated that the whole community was no better at degrading pure cellulose than two members in pure culture. Since the full potential of the community may not be expressed on pure cellulose, breakdown and enzyme production was investigated during growth on lignocellulose. A large proportion of lignocellulosic material consists of xylan and enzymes capable of degrading this component were investigated. The highest percentage degradation and enzyme production (with the exception of Β-glucosidase) after 15 d growth on straw was achieved by the same three cultures. Studies of their growth on hay and straw were extended over a 60-d period. The rate and extent of degradation of hay by P. simplicissimum and A. fumigatus was similar to that of the mixed culture, more than 40% degradation occurring in 40 d. However, differences in levels of enzyme activity were observed. The mixed culture produced lower levels of enzyme activity (with the exception of Β-glucosidase) particularly during the initial states of degradation. Differences in enzyme production by A. fumigatus and P. simplicissimum were also observed. A. fumigatus produced high levels of xylanase and endoglucanase while P. simplicissimum produced high levels of exoglucanase. Similar results were observed on straw. The composition of the lignocellulosic material was measured by sequential chemical extraction of the solubles, hemicellulose, cellulose, and lignin. Changes in the composition during degradation were investigated. During the growth of all three cultures on hay, the total percentage of hemicellulose and cellulose decreased from 84% to less than 45% in 40 d. Despite significant differences in the enzyme activity, P. simplicissimum, A. fumigatus and the mixed culture were capable of degrading lignocellulosic material at the same rate. The production of a full cellulase complex appears to be more important than the production of high levels of individual enzymes.     

The effect of stress on multiple bifurcations in ideal crystals

Phase changes involving bifurcation of an internal variable are discussed. It is shown that one particular type of such bifurcation is likely to be preferred above the others, and we present an analysis of the effect of applied stress on that type of bifurcation. Connections are made between the internal (microscopic) picture and the thermoelastic (macroscopic) picture of the phenomenon.     

Photon noise limitations on the recovery of stellar images by speckle interferometry

The signal-to-noise ratio in steliar speckle interferometry is estimated by direct application of photon counting formulae. This treatment demonstrates that the limiting observable magnitudes are dependent on object size.     

Intrusion of fluids into nanogrooves

We study the shape of gas-liquid interfaces forming inside rectangular nanogrooves (i.e., slit-pores capped on one end). On account of purely repulsive fluid-substrate interactions the confining walls are dry (i.e., wet by vapor) and a liquid-vapor interface intrudes into the nanogrooves to a distance determined by the pressure (i.e., chemical potential). By means of Monte Carlo simulations in the grand-canonical ensemble (GCEMC) we obtain the density ρ(z) along the midline (x = 0 of the nanogroove for various geometries (i.e., depths D and widths L of the nanogroove. We analyze the density profiles with the aid of an analytic expression which we obtain through a transfer-matrix treatment of a one-dimensional effective interface Hamiltonian. Besides geometrical parameters such as D and L , the resulting analytic expression depends on temperature T , densities of coexisting gas and liquid phases in the bulk ρ^g,l _x and the interfacial tension γ . The latter three quantities are determined in independent molecular dynamics simulations of planar gas-liquid interfaces. Our results indicate that the analytic formula provides an excellent representation of ρ(z) as long as L is sufficiently small. At larger L the meniscus of the intruding liquid flattens. Under these conditions the transfer-matrix analysis is no longer adequate and the agreement between GCEMC data and the analytic treatment is less satisfactory.