The effect of the incubation period on the result of MPN enumerations of nitrite-oxidizing bacteria: theoretical considerations

Abstract A computer model based on Monod- and Haldane-kinetics was used to estimate the minimum incubation period required for MPN enumerations of nitrite-oxidizing bacteria. The minimum incubation period was defined as the time needed for one cell, present in the tubes inoculated with the highest dilutions, to grow into a population that oxidized all the nitrite present at the start of the incubation. Kinetic parameters used in the model were derived from literature data and applied in different combinations. The results show that the minimum incubation period may increase with decreasing initial nitrite concentrations in the incubation medium. They also show that the opposite trend, i.e. increasing minimum incubation periods with increasing nitrite concentration periods with increasing nitrite concentration, can be explained by introducing a term for substrate inhibition in the model. A MPN enumeration result obtained with samples from a waterlogged peat bog soil could only partly be explained by the model if only one set of parameters was used. This indicates that the community of nitrite-oxidizing bacteria in this soil is composed of at least two types of nitrite-oxidizing bacteria, with different kinetic parameters of nitrite oxidation and growth.     

Measurement of SCE frequencies in plants: a simple Feulgen-staining procedure for vicia faba

A relatively straightforward approach is described to obtain differential contrast in sister chromatids for SCE detection in Vicia faba after BrdUrd incorporation. The hydrolysis time of the well-known Feulgen reaction was extended to differentially degrade the DNA, the BrdUrd-substituted strands being more resistant. The procedure may easily be adapted for other plant species with large chromosomes.     

Exposure assessment of electromagnetic fields near electrosurgical units

Electrosurgical units (ESU) are widely used in medical health services. By applying sinusoidal or pulsed voltage in the frequency range of 0.3–5 MHz to the electrode tip, the desired mixture of coagulation and cutting are achieved. Due to the high voltage and current in the cable, strong electromagnetic fields appear near the ESU. The surgeon and others inside the operating room such as nurses, anesthesiologists, etc., will be highly exposed to these fields. The stray fields surrounding the ESU have previously been measured, but now a deeper analysis has been made of the curve shape of the field and the implication of this when assessing exposure from a commonly used ESU in accordance with the International Commission on Non‐Ionizing Radiation Protection (ICNIRP) guidelines. The result showed that for some of the modes, especially those using high‐pulsed voltage with only a few sinusoidal periods, the E‐field close to the cable could reach linear spatially averaged values of 20 kV/m compared to the 2.1 kV/m stated in ICNIRP guidelines. Assessing the E‐ and B‐field from ESU is not straightforward since in this frequency range, both induced current density and specific absorption rate are restricted by the ICNIRP guidelines. Nevertheless, work needs to be done to reduce the stray fields from ESU. Bioelectromagnetics 31:513–518, 2010. © 2010 Wiley‐Liss, Inc.