J.R. Medina

Mutants of Azotobacter vinelandii altered in the regulation of nitrate assimilation

The two enzymes involved in the assimilatory pathway of nitrate in Azotobacter vinelandii are corregulated. Nitrate reductase and nitrite reductase are inducible by nitrate and nitrite. Ammonium represses induction by nitrate of both reductases. Repression by ammonium is higher in media containing 2-oxo-glutarate as carbon source than in media containing sucrose. Mutants in the gene ntrC lost nitrate and nitrite reductase simultaneously. Ten chlorate-resistant mutants with a new phenotype were isolated. In media without ammonium they had a normal phenotype, being sensitive to the toxic effect of chlorate. In media containing low ammonium concentrations they were resistant to chlorate. These mutants seem to be affected in the repression of nitrate and nitrite reductases by ammonium.

Allelic interaction in the photogeotropism of Phycomyces

The angle of a laterally illuminated Phycomyces sporangiophore with the vertical is determined by phototropism and geotropism. For mutants affected in the early steps of the phototransduction process, these angles are the same as in the wild type when light intensities are measured not in absolute units, but relative to the respective thresholds. The angles reached after 6 h of exposure are equilibrium angles for these mutants, but not for mutants affected in the late steps. The behavior of heterokaryons containing wild-type and mutant nuclei is close to that of the wild type for most of the nuclear proportion range. The relationships between photogeotropic equilibrium angle, light intensities, and nuclear proportion are discussed in terms of a simple model for Phycomyces behavior.

Acute otitis media in childhood: A study of 20,532 cases

SummaryWe present a study of acute otitis media among 20,532 Spanish children during a 6-month period from January through June 1991. The study was done by distributing a questionnaire to all Spanish pediatricians. Of the patients 51.7% were girls and 48.3% boys; 68.7% of all children were younger than 5 years. The most frequent symptoms were otalgia or irritability, 92.7%; fever, 63.5%; otorrhea, 24.9%; vomiting, 21.4%; and another concomitant upper respiratory tract infection, 65.5%. Otitis was bilateral in 45.6% of the cases. The most frequently used antibiotic was cefixime (38%), followed by amoxicillin-clavulanate (22.2%), amoxicillin (15.3%), 2nd-generation cephalosporins (13.5%) and macrolides (8.8%). In 11.8% of the patients, a change in the initial antibiotic therapy was required due to adverse effects. Resolution of symptoms occurred in 77.8% of the patients.ZusammenfassungWir berichten über eine Studie zur akuten Otitis media bei 20 532 spanischen Kindern, die während einer Phase von 6 Monaten von Januar bis Juni 1991 durchgeführt wurde. Im Rahmen der Studie wurden Fragebogen an alle spanischen Kinderärzte versandt. 51,7% der Patienten waren Mädchen und 48,3% Jungen. 68,7% aller Kinder waren jünger als 5 Jahre. Die häufigsten Symptome waren Ohrenschmerzen (oder Reizbarkeit) in 92,7%, Fieber in 63,5%, Otorrhoe in 24,9%, Erbrechen in 21,4% und begleitende Infektion der oberen Atemwege in 65,5% der Fälle. Bei 45,6% der Fälle war die Otitis beidseitig. Die am häufigsten verordneten Antibiotika waren Cefixim (38%), Amoxicillin-Clavulansäure (22,2%), Amoxicillin (15,3%), 2. Generations-Cephalosporine (13,5%) und Makrolide (8,8%). Bei 11,8% der Patienten mußte die initiale Antibiotikatherapie wegen Nebenwirkungen umgesetzt werden. Bei 77,8% der Patienten verschwanden die Symptome.We present a study of acute otitis media among 20,532 Spanish children during a 6-month period from January through June 1991. The study was done by distributing a questionnaire to all Spanish pediatricians. Of the patients 51.7% were girls and 48.3% boys; 68.7% of all children were younger than 5 years. The most frequent symptoms were otalgia or irritability, 92.7%; fever, 63.5%; otorrhea, 24.9%; vomiting, 21.4%; and another concomitant upper respiratory tract infection, 65.5%. Otitis was bilateral in 45.6% of the cases. The most frequently used antibiotic was cefixime (38%), followed by amoxicillin-clavulanate (22.2%), amoxicillin (15.3%), 2nd-generation cephalosporins (13.5%) and macrolides (8.8%). In 11.8% of the patients, a change in the initial antibiotic therapy was required due to adverse effects. Resolution of symptoms occurred in 77.8% of the patients. Wir berichten über eine Studie zur akuten Otitis media bei 20 532 spanischen Kindern, die während einer Phase von 6 Monaten von Januar bis Juni 1991 durchgeführt wurde. Im Rahmen der Studie wurden Fragebogen an alle spanischen Kinderärzte versandt. 51,7% der Patienten waren Mädchen und 48,3% Jungen. 68,7% aller Kinder waren jünger als 5 Jahre. Die häufigsten Symptome waren Ohrenschmerzen (oder Reizbarkeit) in 92,7%, Fieber in 63,5%, Otorrhoe in 24,9%, Erbrechen in 21,4% und begleitende Infektion der oberen Atemwege in 65,5% der Fälle. Bei 45,6% der Fälle war die Otitis beidseitig. Die am häufigsten verordneten Antibiotika waren Cefixim (38%), Amoxicillin-Clavulansäure (22,2%), Amoxicillin (15,3%), 2. Generations-Cephalosporine (13,5%) und Makrolide (8,8%). Bei 11,8% der Patienten mußte die initiale Antibiotikatherapie wegen Nebenwirkungen umgesetzt werden. Bei 77,8% der Patienten verschwanden die Symptome.

Conjugal retrotransfer of chromosomal markers inAzotobacter vinelandii

The IncP plasmids R68.45 and pJB3JI mediate retrotransfer (i.e., transfer of chromosomal markers from the recipient bacterium to the original donor) in homologous matings withAzotobacter vinelandii. Retrotransfer is not an early event inAzotobacter. On the contrary, it begins after genetic transfer in the usual direction, i.e., from the donor bacterium to the recipient, has been taking place for some time. Transfer of chromosomal markers mediated by the RP4/Tn5-Mob system does not undergo retrotransfer. The simplest hypothesis compatible with our results is that IncP plasmids that confer a high chromosome-mobilizing ability promote retrotransfer when transferred to the recipient bacteria.

A quantitative model of Phycomyces phototropism.

Abstract A quantitative model accounting for phototropism in the wild type and in behavioural mutants of Phycomyces is described. Photomecisms (changes in the sporangiophores growth velocity in response to changes in light intensity) are produced by a system composed of two sets of linear transducers separated by an adaptation mechanism, the first transducer being the photoreceptor. Phototropism under asymmetrical light distributions is caused by the summation of local photomecisms in the distal half of the sporangiophore, where two bright bands are produced by refraction of the incident light. The photoreceptors turn around the sporangiophore axis; they are approximately adapted to local intensity everywhere except upon entrance to the first bright band. Thus, a continuous photomecism originates at this band while the rest of the sporangiophore remains practically unstimulated. The mutants suffer a reduction in the efficiency of transduction. The behaviour of the wild type and of the mutants has been quantitatively simulated by computer. The predictions from the model fit the experimental results.

A Chromosomal Linkage Map of Azotobacter Vinelandii

SummaryA chromosomal map of Azotobacter vinelandii strain UW was constructed. The map was based on measures of cotransfer of various markers mediated by plasmids R68.45 and pJB3JI, on results obtained from conjugal experiments with R-primes, and on recombinants obtained by chromosomal transfer mediated by RP4/Tn5-Mob.

Light-dependent decrease in alcohol dehydrogenase activity ofPhycomyces

Abstract Specific activities for alcohol dehydrogenase (ADH) are higher in dark-grown than in light-grown cultures of the fungusPhycomyces blakesleeanus. A single electrophoretic band with ADH activity was detected inP. blakesleeanus; this electromorph stained for ADH activity more intensely in dark-grown mycelia than in light-grown mycelia. A protein band, with the same electrophoretic mobility as this unique ADH electromorph, stained more darkly in extracts from unilluminated mycelia than from illuminated mycelia. The light-dependent decrease of ADH activity was normal in fivePhycomyces mutants with altered phototropism (mad genotype). Since two of these strains carry multiple mutations and show extremely reduced phototropism even at light intensities higher than the light intensity used in this work, it is concluded that the light-dependent ADH decrease is not mediated by themad photosystem.

Some comments on the variance of heterozygosity in finite populations

A new and more accurate formula for the variance of heterozygosity under genetic drift has been obtained. The variance can be partitioned into two components; the first comes from the dispersion of the allelic frequencies among populations, and the second from the dispersion of the actual heterozygosity, h, around their expected values, 2pq. A certain generation exists where the variance reaches a maximum; thus, the genetic drift can be split into two phases by this single maximum.

Alcohol dehydrogenase activity and carotenogenesis in Phycomyces

Abstract The specific activity of alcohol dehydrogenase (ADH) is increased when carotenogenesis is made defective either by car mutations or by diphenylamine treatment in Phycomyces blakesleeanus . The increase in specific activity occurs whether cultures are grown in the dark or in the light. In the wild type, ADH specific activity is higher in dark-grown than in light-grown mycelia. The car mutants exhibit a normal light-induced ADH decrease.

Males and the two-fold disadvantage of dioecy

We propose that males are the causative agent of a short-term evolutionary advantage of dioecius over parthenogenetic lines. A simple model to account for selection against parthenogenetic females due to the sexual activities of males is presented. Many known aspects of the biology of parthenogenesis that agree nicely with the model presented here are discussed.