Masayuki Seto

Relationship between rate of carbon dioxide evolution, microbial biomass carbon, and amount of dissolved organic carbon as affected by temperature and water content of a forest and an arable soil

Abstract Using an Ochrept soil of a forest at climax stage or of an arable site at Kita‐Ibaraki, a city in central Japan, the rates of carbon dioxide (CO2)‐carbon (C) evolution, the amounts of microbial biomass carbon (MBC) and the amounts of dissolved organic carbon (DOC) were measured in a laboratory with special reference to the incubation temperature and the soil water content. The rates of CO2‐C evolution increased exponentially with increase in the incubation temperature in the range of 4–40°C. The temperature coefficients (Q10) were 2.0 for the forest and 1.9 for the arable soil. The amounts of MBC were almost constant of 980 μg g‐1 soil in the incubation temperature up to 25°C for the forest, and 340 μg g‐1 soil in the incubation temperature up to 31 °C for the arable soil. The amounts of DOC in soil solutions were almost constant at 3.1 μg g‐1 soil in the incubation temperature up to 25°C for the forest, and 3.8 μg g‐1 soil in the incubation temperature up to 31°C for the arable soil. The rates o...

Estimation of the yield coefficient of Pseudomonas sp. strain DP-4 with a low substrate (2,4-dichlorophenol [DCP]) concentration in a mineral medium from which uncharacterized organic compounds were eliminated by a non-DCP-degrading organism.

ABSTRACT The yield coefficient (YC) of Pseudomonas sp. strain DP-4, a 2,4-dichlorophenol (DCP)-degrading organism, was estimated from the number of CFU produced at the expense of 1 unit amount of DCP at low concentrations. At a low concentration of DCP, the YC can be overestimated in pure culture, because DP-4 assimilated not only DCP but also uncharacterized organic compounds contaminating a mineral salt medium. The concentration of these uncharacterized organic compounds was nutritionally equivalent to 0.7 μg of DCP-C ml−1. A mixed culture with non-DCP-degrading organisms resulted in elimination of ca. 99.9% of the uncharacterized organic compounds, and then DP-4 assimilated only DCP as a substrate. In a mixed culture, DP-4 degraded an initial concentration of 0.1 to 10 μg of C ml of DCP−1 and the number of CFU of DP-4 increased. In the mixed culture, DCP at an initial concentration of 0.07 μg of C ml−1 was degraded. However, the number of CFU of DP-4 did not increase. DCP at an extremely low initial concentration of 0.01 μg of C ml−1 was not degraded in mixed culture even by a high density, 105 CFU ml−1, of DP-4. When glucose was added to this mixed culture to a final concentration of 1 μg of C ml−1, the initial concentration of 0.01 μg of C ml of DCP−1 was degraded. These results suggested that DP-4 required cosubstrates to degrade DCP at an extremely low initial concentration of 0.01 μg of C ml−1. The YCs of DP-4 at the expense of DCP alone decreased discontinuously with the decrease of the initial concentration of DCP, i.e., 1.5, 0.19, or 0 CFU per pg of DCP-C when 0.7 to 10, 0.1 to 0.5, or 0.07 μg of C ml of DCP−1 was degraded, respectively. In this study, we developed a new method to eliminate uncharacterized organic compounds, and we estimated the YC of DP-4 at the expense of DCP as a sole source of carbon.

Growth and respiratory activity of mold fungus (Trichoderma lignorum)

The growth ofTrichoderma lignorum was studied in relation to the carbon balance of the culture system and the respiratory activity at different growth phases.Conidia, after inoculation into the medium, swelled and germinated rapidly. The growth rate of the hyphae at the exponential phase was 0.46 hr−1 (2.2 hr for mass doubling) at 25 C. The yield efficiency of hyphal biomass-C at the cost of glucose-C was 67%, while those of the waste products-C excreted and of CO2-C evolved were, 6.5% and 26.5%, respectively. The yield efficiency of conidia-C to the decrease of hyphae-C was 34%. The germination, growth rate and carbon balance were not affected by different concentrations of glucose from 10 to 2×103 mg glucose-C/l.Carbon dioxide was needed as the growth factor for the initiation of the germination of conidia, but there was no increase in yield efficiency as a result of CO2 fixation.The respiratory rate of the fungus changed drastically as the growth proceeded. The rate of endogenous respiration of conidia was less than 0.2 mg CO2-C/g conidia-C/hr which increased immediately after inoculation into the medium. The highest respiratory rate of hyphae (100–110 mg CO2-C/g hyphae-C/hr) was obtained throughout the exponential phase. Thereafter, decreasing rapidly, the respiratory rate of submerged hyphae of 1-week-old showed only 1.8 mg CO2-C/g biomass-C/hr, whereas the rate of aerial hyphae forming conidia increased again, but did not exceed 10 mg CO2-C/g biomass-C/hr.

Estimation of cellular protein for monitoring the cell growth of bacteria in a photo-crosslinked polymer resin

Abstract The growth of bacterial cells immobilized in a photo-crosslinked polymer was estimated on the basis of proteins after hydrolysis of the polymer with alkaline solution. Hydrophobic interaction column chromatography was employed to separate the protein fraction from the hydrolyzed polymer. The amount of cells immobilized in the resin can be precisely estimated on the basis of this procedure.

The effect of density and starvation of a bacterial population on the rate constant of second-order kinetics

where So is the substrate concentration at time zero. The application of the equation seems promising as a method for predicting the decomposition of various xenobiotics in the natural environment (Paris et al., 1981 ; Tiedje, 1980), where So is very low and Bo is constant over the time period concerned. However, certain limitations with the application of the kinetics have been suggested, i.e. inapplicability of the kinetics to transient (batch) bacterial growth which induces erroneous estimates of _Ks if maintenance requirements are ignored (Robinson and Tiedje, 1983)and inapplicability to populations requiring induction before the onset of metabolism (Simkins and Alexander, 1984). The present study points out another limitation, i.e. the value of k is no longer a constant when either the bacterial density or the age of the culture varies. Therefore, the necessity was discussed of expressing the ecophysiological status of the bacterial population as one of the determinative parameters in the kinetic equation.