Effect of voltage and oxygen on inactivation of E. coli and S. typhi using pulsed dielectric barrier discharge.

This work presents the study of the voltage and oxygen effect on bacterial inactivation in water using a pulsed dielectric barrier discharge (DBD) under atmospheric pressure, where Escherichia coli (E. coli) and Salmonella typhi (S. typhi) bacteria were used as model microorganisms. A cylindrical DBD reactor was developed and tested in applications to assay the efficiency of bacterial inactivation in water on a volume of 500 mL flowing continuously throughout the system assisted with a peristaltic pump at 4.4 ± 0.1 mL/s. The efficiency of the treatment reached a 6-log10 reduction for both E. coli and S. typhi bacteria at 106 CFU/mL of concentration at the end of the first cycle of treatment at a minimum voltage of 12 kV with oxygen bubbling gas, concluding that there was a minimum voltage to produce inactivation of E. coli and S. typhi samples. Bacterial inactivation without the oxygen condition contrasted with the high rate of inactivation with oxygen at relatively low voltage discharges.

Maximum-likelihood models for mapping genetic markers showing segregation distortion. 1. Backcross populations.

A maximum-likelihood approach is used in order to estimate recombination fractions between markers showing segregation distortion in backcross populations. It is assumed that the distortions are induced by viability differences between gametes or zygotes due to one or more selected genes. We show that Bailey's (1949) estimate stays consistent and efficient under more general assumptions than those defined by its author. This estimate should therefore be used instead of the classical maximum-likelihood estimate. The question of detection of linkage is also discussed. We show that the order of markers on linkage groups may be affected by segregation distortion.

Maximum-likelihood models for mapping genetic markers showing segregation distortion. 2. F2 populations.

In F2 populations, gametic and zygotic selection may affect the analysis of linkage in different ways. Therefore, specific likelihood equations have to be developed for each case, including dominant and codominant markers. The asymptotic bias of the "classical" estimates are derived for each case, in order to compare them with the standard errors of the suggested estimates. We discuss the utility and the efficiency of a previous model developed for dominant markers. We show that dominant markers provide very poor information in the case of segregation distortion and, therefore, should be used with circumspection. On the other hand, the estimation of recombination fractions between codominant markers is less affected by selection than is that for dominant markers. We also discuss the analysis of linkage between dominant and codominant markers.

A molecular approach to unraveling the genetics of sugarcane, a complex polyploid of the Andropogoneae tribe.

Modern sugarcane varieties are complex aneuploids and typically have chromosome numbers in the 100-125 range with about 5-10% of them contributed by wild relatives, mainly Saccharum spontaneum, and the rest by S. officinarum. This particular genomic constitution was found favorable for mapping the S. spontaneum genome, using maize as a diploid reference for comparison. We conducted an analysis of 32 individuals derived from the selfing of variety SP 701006 using four isozymes and 53 maize probes which covered the whole maize genome. A total of 348 segregating bands were generated. Highly significant cosegregations enabled us to place 94 markers into 25 cosegregation groups. Eighteen of these groups involved S. spontaneum specific markers and might therefore mark S. spontaneum chromosomes in segregation. On the basis of probes in common, the 25 cosegregation groups could be assembled into eight tentative linkage groups, of which seven describe S. spontaneum chromosomes. A large degree of synteny between sugarcane and maize could be inferred, with a much lower rate of recombination in sugarcane.