Origin of sexual isolation in <Emphasis Type="Italic">Drosophila ananassae</Emphasis> due to founder effects

The origin of sexual isolation is the central event in the evolution of biological species and plays a key role in maintaining biological diversity. Three mass culture stocks of D. ananassae originating from different geographic localities showing no isolation with each other were subjected to different degrees of bottlenecks i.e. one pair, five pairs and ten pairs. These drift lines were passed through flush-crash cycle at every generation with same initial number of founders, and maintained for twenty-seven generations and then the pattern of matings was tested among these nine drift lines involving 36 crosses in total. In 23 of 36 crosses, the difference between homogamic and heterogamic matings was significant and isolation indices were significantly more than zero in one direction only providing evidence for asymmetrical sexual isolation. Further, when Bonferroni test for pair-wise analysis was employed, significant differences between homogamic and heterogamic matings were found in 25 crosses. These findings provide evidence for origin of sexual isolation by founder effects in D. ananassae.     

THE POTENTIAL FOR GENETIC EXCHANGE BY TRANSFORMATION WITHIN A NATURAL POPULATION OF BACILLUS SUBTILIS

We have investigated the potential for genetic exchange by transformation within a Mojave Desert population of Bacillus subtilis. Almost all strains surveyed were competent for transformation, and the strains varied over almost three orders of magnitude in their levels of competence. This high degree of variation suggests that natural selection toward an optimal level of competence is, at most, very weak in this population. Six of 24 competent strains showed sexual isolation from laboratory strain 168 (i.e., heterogamic transformation was reduced). Direct crosses between selected pairs of Mojave strains indicated sexual isolation within the Mojave population. Levels of sexual isolation observed within this population of B. subtilis were much less than those previously observed for transformation between named Bacillus species. Sexual isolation between 168 and Mojave strains, and among Mojave strains, was due to differences in restriction-modification systems and to DNA sequence divergence.     

Use of a packed-column bioreactor for isolation of diverse protease-producing bacteria from antarctic soil

Seventy-five aerobic heterotrophs have been isolated from a packed-column bioreactor inoculated with soil from Antarctica. The column was maintained at 10 degrees C and continuously fed with a casein-containing medium to enrich protease producers. Twenty-eight isolates were selected for further characterization on the basis of morphology and production of clearing zones on skim milk plates. Phenotypic tests indicated that the strains were mainly psychrotrophs and presented a high morphological and metabolical diversity. The extracellular protease activities tested were optimal at neutral pH and between 30 and 45 degrees C. 16S ribosomal DNA sequence analyses showed that the bioreactor was colonized by a wide variety of taxons, belonging to various bacterial divisions: alpha-, beta-, and gamma-Proteobacteria; the Flexibacter-Cytophaga-Bacteroides group; and high G+C gram-positive bacteria and low G+C gram-positive bacteria. Some strains represent candidates for new species of the genera Chryseobacterium and Massilia. This diversity demonstrates that the bioreactor is an efficient enrichment tool compared to traditional isolation strategies.     

Effect of ambient temperature on serum prolactin and luteinizing hormone levels during the reproductive life cycle of the female turkey (Meleagris gallopavo)

An ambient temperature of 30 degrees C compared to 18 degrees C accelerated the increase in serum prolactin (Prl) level induced by photostimulation of female turkeys. The contribution of reproductive stage and nesting behavior to this serum Prl elevation was assessed by housing adult female turkeys in individual wire cages while allowing other females free access to nests on the floor. Birds of both groups were exposed to 10 degrees C, 24 degrees C or 30 degrees C beginning 4 wk prior to photostimulation and continuing throughout the reproductive phase. Lapsed time between the onset of photostimulation and onset of sexual maturity, and between the onset of sexual maturity and onset of incubation behavior was shorter in birds housed at 30 degrees C with access to nests than in corresponding birds housed at 24 degrees C and 10 degrees C. The increases in serum Prl associated with sexual maturity or incubation behavior occurred at a greater rate in the birds maintained at 30 degrees C. Cage-reared birds had the same lapsed time between onset of photostimulation and onset of sexual maturity and the same sustained low Prl level regardless of ambient temperature exposure. All groups exhibited similar luteinizing hormone profiles. These findings indicate that the accelerated increase in Prl under elevated temperature in floor-reared turkeys is related to accelerated development of reproductive function, and not the direct effect of ambient temperature on mechanisms controlling Prl.     

Sex determination in hydra: control by a subpopulation of interstitial cells in Hydra oligactis males

The stability of sexual phenotype was examined in a single clone of Hydra oligactis males maintained at two culture temperatures, 18 and 22 degrees C. At these temperatures animals of this species do not reproduce sexually, but reproduce asexually by budding, and males and females are morphologically indistinguishable. When the temperature is lowered to 10 degrees C gametogenesis is induced and sexual phenotype can be assayed. Males cultured for several years at 18 degrees C expressed a stable sexual phenotype when induced to undergo gametogenesis; males remained male. Those cultured at 22 degrees C for 1 year, however, expressed a low frequency of sex reversal from male to female; males ceased sperm differentiation and began producing eggs. Male sex reversal in cultures maintained at the higher temperature was correlated with the loss of a specific subpopulation of interstitial cells, those that bind the monoclonal antibody, AC2, which labels cells specific to the spermatogenic pathway in H. oligactis males. When interstitial cells restricted to this pathway were reintroduced into sex-reversed males (phenotypic females), the male phenotype was reestablished and animals reverted to sperm production. To further investigate the role of AC2+ cells in the masculinization of females, normal males (containing AC2+ cells) and sex-reversed males (lacking AC2+ cells) were grafted to females. In grafts between normal males and females, egg production ceased and sperm differentiation ensued, whereas those between sex-reversed males and females continued to produce eggs. Thus, the presence of AC2+ interstitial cells is strictly correlated with male sexual phenotypes and it is only in their absence that the female phenotype is expressed.     

Haldane's rule by sexual transformation in Caenorhabditis

Haldane's rule in C. briggsae x C. remanei broods was caused by sexual transformation; XX and XO hybrids were female. C. briggsae and C. remanei variants that partially suppress hybrid sexual transformation were identified. Effects of variant strains were cumulative. Hence, aberrant sex determination is a reproductive isolation mechanism in Caenorhabditis.     

Symmetrical and asymmetrical sexual isolation among laboratory strains of Drosophila ananassae

Male-choice experiments using five isofemale lines of Drosophila ananassae originating from different localities were performed to study sexual isolation within the species. In most of the crosses homogamic matings outnumber heterogamic ones, and deviation from randomness is statistically significant in 11 of 20 crosses. This provides evidence for positive assortative mating within D. ananassae. Isolation indices range from -0.057 to 0.555. Eleven positive isolation indices are significantly greater than zero. Both types of sexual isolation, symmetrical and asymmetrical, have been observed among different strains. Thus the present results clearly indicate that the laboratory strains of D. ananassae have developed behavioural reproductive isolation as a result of genetic divergence.     

The Log-Linear Relationship between Sexual Isolation and Sequence Divergence in Bacillus Transformation Is Robust

The relationship between sexual isolation and sequence divergence in Bacillus transformation was previously shown to be log linear. In the present study, we have shown that this relationship is robust with respect to naturally occurring genetic variation among recipient strains of Bacillus subtilis and B. mojavensis. Naturally occurring restriction endonuclease activity was shown not to affect this relationship. Also, seven out of eight recombination mutants tested for their sensitivity to sequence divergence have shown the same relationship between sequence divergence and sexual isolation; a mutant for recH was more sensitive to sequence divergence, suggesting that the product of this gene may be involved in resolution of mismatches in heterogamic transformation. We have also shown that the relationship between sexual isolation and sequence divergence is robust with respect to variation in the conditions of transformation, including variation in the length of donor DNA, the concentration of donor DNA, and intracellular competition between donor-derived and recipient-derived DNA. The robustness of the relationship between sexual isolation and sequence divergence among naturally occurring strains and across transformation conditions allows us to predict the eventual outcome of sequence divergence among B. subtilis and its closest relatives.     

Characterization of suppressible mutations in the viomycin phosphotransferase gene of the Streptomyces enteric plasmid pVE138.

The viomycin phosphotransferase gene (vph) is expressed and confers resistance to viomycin in both Streptomyces spp. and members of the family Enterobacteriaceae. We report the isolation of UGA (opal) and UAG (amber) mutations in the vph gene of shuttle plasmid pVE138. We found that the five UGA mutations in vph resulted in a temperature-sensitive phenotype in Salmonella typhimurium. Su- strains are Vior at 28 degrees C and Vios at 37 degrees C, whereas Su+UGA strains are Vior at both 28 and 37 degrees C. The single amber mutation isolated was not temperature sensitive and resulted in the expected Vios phenotype in Su- strains and Vior in Su+UAG strains.     

Stability of feline caliciviruses in marine water maintained at different temperatures

Since human caliciviruses are responsible for viral gastroenteritis transmitted by contaminated foods and the viruses barely propagate in cell culture, feline caliciviruses were employed as a model for the measurement of their stability in marine water. Survival of four strains of feline calicivirus in marine water was measured when the seed viruses were diluted 1/10 with marine water and maintained at 4 degrees C, 10 degrees C, and 20 degrees C respectively. Among the virus strains studied, a considerable amount of infective viruses remained at 10 degrees C or lower temperature conditions even for a period of 30 days.     

Use of Genomic Exclusion to Isolate Heat-Sensitive Mutants in Tetrahymena

We have used the abnormal form of conjugation known as "genomic exclusion" to isolate a collection of heat-sensitive mutants of Tetrahymena pyriformis, syngen 1. Growth at room temperature in bacterized medium and no growth at 40 degrees C in the same medium was the criterion used for the isolation. The mutant strains were tested for growth in pure (axenic) culture in proteose peptone medium; of the 31 strains which grew normally at room temperature and not at 40 degrees C in that medium, 21 also failed to grow at 37 degrees C. Preliminary results of complementation tests suggest that most, if not all, the mutations are recessive and that a variety of genes was affected. A detailed genetic analysis was performed on one mutant (H9). The results are all consistent with the idea that the heat-sensitive phenotype of this mutant is determined by a single recessive mutation, designated ts-2. Heterozygotes ts-2/+ yield heat-sensitive segregants during vegetative growth; we interpret this finding as another example of allelic exclusion, a phenomenon universally encountered among heterozygotes in syngen 1 of T. pyriformis. Our results are discussed in the context of some questions of current interest in Tetrahymena genetics.     

Minimum growth temperatures of Listeria monocytogenes and non-haemolytic Listeria

Minimum growth temperatures and those of decreased growth were determined for 100 strains of listerias. The ability of 78 strains of Listeria monocytogenes isolated from animals and 22 non-haemolytic strains to grow at low temperatures was studied, using a flooding technique, in a plate-type continuous temperature gradient incubator at temperatures between -1.6 and 14.5 degrees C. The mean minimum temperature for L. monocytogenes was +1.7 +/- 0.5 degrees C. The growth of non-haemolytic listerias was unobservable at +1.7 +/- 0.5 degrees C. The L. monocytogenes strains grew at about 0.6 degrees C lower than the non-pathogenic strains. No differences in growth temperatures were observed among L. monocytogenes strains isolated from different sources. The serovars with the OI antigen grew at lower temperatures (+1.0 +/- 0.3 degrees C) than the other common serovar 4b (+1.3 +/- 0.4 degrees C). The results indicate that L. monocytogenes grows better than non-haemolytic strains under cold conditions. The possible role of haemolysins as growth factors is also discussed.     

Intraspecific sexual isolation in Drosophila.

Intraspecific sexual isolation was examined among wild strains of Drosophila malerkotliana, D. parabipectinata and D. pseudoananassae by multiple-choice method in Elens-Wattiaux mating chamber. In D. pseudoananassae, mating between two strains tested was random and isolation estimate was close to one. In one out of 6 crosses, involving geographic strains of D. malerkotliana, there was significant deviation from randomness and isolation estimate remained low which shows non-random (preferential or positive assortative) mating. In D. parabipectinata, the deviation from randomness was statistically significant due to higher number of homogamic matings in three crosses involving wild strains derived from geographically distant places and isolation estimate remained low in these crosses. The results provide evidence for incipient sexual isolation within D. malerkotliana and D. parabipectinata as a result of genetic divergence.     

提高产抗生素链霉菌紫外诱变正变率的研究

将UV诱变了的产抗生素链霉菌（Streptomyces sp.）AP 19-1菌株之孢子,置于适宜的生长温度27℃与接近抑制生长的胁迫温度33℃下培养,结果表明：在33℃下生长获得的子代菌株中,产抗生素水平超过其出发菌株的正向突变体所占的比例,明显比在27℃下培养的高。27℃下培养,正向突变体占总子代菌株数的25.8%,而在33℃下培养则为58.1%。用17种随机引物对出发菌株与UV诱变子代菌株进行总DNA的RAPD测验证明,在接近抑制生长的温度33℃下培养获得的子代,发生在其DNA水平上的变异程度比在27℃的要高得多。这一方法能较大幅度提高链霉菌紫外诱变育种的工作效率,同时也为链霉菌经紫外诱变后突变形成机制的进一步研究提供了新途径。Abstract: UV irradiated spores of Streptomyces sp. AP 19 -1 strain that can produce antibiotics were incubated at 27 ℃, and 33 ℃ which is close to inhibiting growth temperature, respectively. The results showed that there were much more forward mutants, whose level of producing antibiotics is higher than that of original strain, among the offspring of UV irradiated spores grown at 33 ℃, compared to that grown at 27 ℃. The percentage of the forward mutants was 25.8 % at 27 ℃ and 58.1% at 33 ℃. The progeny strains and the original strain were tested by RAPD using total DNA with 17 primers. It was demonstrated that more variations occurred in the chromosomal DNA of the progeny strains grown at 33 ℃ than in that at 27 ℃. This method facilitates increasing the efficiency of induced mutagenesis in breeding and provides a new way to study the mechanisms of mutation formation in UV irradiated Streptomyces sp. cells.     

Influence of Storage at Freezing and Subsequent Refrigeration Temperatures on beta-Galactosidase Activity of Lactobacillus acidophilus

The ability of three strains of Lactobacillus acidophilus to survive and retain beta-galactosidase activity during storage in liquid nitrogen at -196 degrees C and during subsequent storage in milk at 5 degrees C was tested. The level of beta-galactosidase activity varied among the three strains (0.048 to 0.177 U/10 organisms). Freezing and storage at -196 degrees C had much less adverse influence on viability and activity of the enzyme than did storage in milk at 5 degrees C. The strains varied in the extent of the losses of viability and beta-galactosidase activity during both types of storage. There was not a significant interaction between storage at -196 degrees C and subsequent storage at 5 degrees C. The strains that exhibited the greatest losses of beta-galactosidase activity during storage in milk at 5 degrees C also exhibited the greatest losses in viability at 5 degrees C. However, the losses in viability were of much greater magnitude than were the losses of enzymatic activity. This indicates that some cells of L. acidophilus which failed to form colonies on the enumeration medium still possessed beta-galactosidase activity. Cultures of L. acidophilus to be used as dietary adjuncts to improve lactose utilization in humans should be carefully selected to ensure that adequate beta-galactosidase activity is provided.     

Growth of epizootic hemorrhagic disease, akabane, and ephemeral fever viruses in Aedes albopictus cells maintained at various temperatures

The growth curves of one epizootic hemorrhagic disease (EHD) virus serotype (Reoviridae), two Akabane virus strains (Bunyaviridae) and three bovine ephemeral fever (BEF) group viruses (Rhabdoviridae) were determined in Aedes albopictus cells maintained at 15, 20, 28 and 33 degrees C. Ae albopictus cells supported the growth of all the viruses although not necessarily at all temperatures. Because none of the viruses exhibited cytopathic effect in Ae albopictus cells, growth was assayed in baby hamster kidney 21 (BHK21) cells maintained at 37 degrees C. The temperature at which the Ae albopictus cells were maintained had a marked effect on the growth and yield for each virus studied. EHD virus was heat-stable and grew after 4 days at 28 and 33 degrees C, and after 8 days at 20 degrees C. No growth was recorded up to 12 days at 15 degrees C. The two Akabane viruses were heat-sensitive and exhibited different growth patterns. One strain (B8935) showed no growth at 15 degrees C and only minimal growth at 20, 28 and 33 degrees C. The other strain (CSIRO 16) showed growth after 1-2 days at all temperatures with higher titres reached at 15 and 20 degrees C than at 28 and 33 degrees C. The BEF group viruses grew to approximately the same titres at all temperatures. At the higher temperatures (28 and 33 degrees C) most of BEF group viruses had disappeared within 9 days. In contrast at the lower temperatures (15 and 20 degrees C), there was still virus present 18 days after inoculation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Genetic transfer by conjugation in the thermophilic green sulfur bacterium Chlorobium tepidum.

The broad-host-range IncQ group plasmids pDSK519 and pGSS33 were transferred by conjugation from Escherichia coli into the thermophilic green sulfur bacterium Chlorobium tepidum. C. tepidum exconjugants expressed the kanamycin and ampicillin-chloramphenicol resistances encoded by pDSK519 and pGSS33, respectively. Ampicillin resistance was a particularly good marker for selection in C. tepidum. Both pDSK519 and pGSS33 were stably maintained in C. tepidum at temperatures below 42 degrees C and could be transferred between C. tepidum and E. coli without modifications. Conjugation frequencies ranged from 10(-1) to 10(-4) exconjugants per donor cell, and frequencies of 10(-2) to 10(-3) were consistently obtained when ampicillin resistance was used as a selectable marker. Methods for growth of C. tepidum on agar, isolation of plating strains and antibiotic-resistant mutants of wild-type C. tepidum cells, and optimum conditions for conjugation were also investigated.     

Campylobacter jejuni survival in chicken meat as a function of temperature.

Recognition of Campylobacter fetus subsp. jejuni (referred to hereafter as C. jejuni) as an important human pathogen and its isolation from meat products indicate the need for knowledge of its survival characteristics in meats. Thermal death times (D-values) for a single strain and a five-strain composite were determined in 1% peptone and autoclaved ground chicken meat at temperatures ranging from 49 to 57 degrees C. Survival was determined for these strains in chicken meat at 4, 23, 37, and 43 degrees C. Survival was also determined on raw chicken drumsticks stored at 4 degrees C in either an ambient or a CO2 atmosphere. D-values were greater in chicken meat than in peptone in all cases. D-values in peptone for strain H-840 at 49, 51, 53, 55, and 57 degrees C were 15.2, 4.90, 1.71, 0,64, and 0.25 min, respectively. The corresponding D-values in ground chicken meat were 20.5, 8.77, 4.85, 2.12, and 0.79 min, respectively. Similar results were obtained with a composite of five strains. When sterile ground chicken meat was inoculated with approximately 10(6) to 10(7) C. jejuni cells per g and stored at 37 degrees C in an ambient atmosphere, a 1-to 2-log count increase occurred during the first 4 days, followed by a gradual decline of about 1 log during the remainder of the 17-day storage period. No growth was observed among similarly inoculated samples that were stored at 4, 23, and 43 degrees C but counts declined by about 1 to 2 logs at 4 degrees C (17 day), by 2.5 to 5 logs at 23 degrees C (17 days), and to undetectable levels at 43 degrees C (between 10 and 16 days). Survival on raw chicken drumsticks stored at 4 degrees C in CO2 and in an ambient atmosphere declined by about 1.5 and 2.0 logs, respectively, during 21 days of storage. The effect of temperature on the survival of C. jejuni in chicken meat was similar to that reported in other natural and laboratory milieus. Ordinary cooking procedures that destroy salmonellae would be expected to destroy C. jejuni.     

Screening and distributing features of bacteria with hydantoinase and carbamoylase

Hydantoinase and carbamoylase are key biocatalysts for the production of optically pure amino acids from dl-5-substituted hydantoins (SSH). Out of 364 isolated strains with hydantoinase and carbamoylase at 45 degrees C, 24 strains showed efficient hydantoinase and carbamoylase activities. Among them, 17 produced l-amino acids, and 7 produced d-amino acids from both aromatic dl-5-benzylhydantoin and aliphatic dl-5-isopropylhydantoin. Most of the strains that were able to form l-amino acid belonged to genera Bacillus, Geobacillus, Brevibacillus, Aneurinibacillus, Microbacterium, and Kurthia. Phylogenetic relationships were investigated based on 16S rRNA from the hydantoinase-producing bacteria. Distinct tendencies toward certain genera were observed between most of the strains forming l-amino acids and d-amino acids from SSH. The results from this study can be utilized to develop new isolation technology of hydantoinase-producing microorganisms, and to understand metabolism and evolutionary origins of hydantoinase and carbamoylase among different bacteria.     

Isolation and characterization of an Escherichia coli mutant having temperature-sensitive farnesyl diphosphate synthase.

The screening of a collection of highly mutagenized strains of Escherichia coli for defects in isoprenoid synthesis led to the isolation of a mutant that had temperature-sensitive farnesyl diphosphate synthase. The defective gene, named ispA, was mapped at about min 10 on the E. coli chromosome, and the gene order was shown to be tsx-ispA-lon. The mutant ispA gene was transferred to the E. coli strain with a defined genetic background by P1 transduction for investigation of its function. The in vitro activity of farnesyl diphosphate synthase of the mutant was 21% of that of the wild-type strain at 30 degrees C and 5% of that at 40 degrees C. At 42 degrees C the ubiquinone level was lower (66% of normal) in the mutant than in the wild-type strain, whereas at 30 degrees C the level in the mutant was almost equal to that in the wild-type strain. The polyprenyl phosphate level was slightly higher in the mutant than in the wild-type strain at 30 degrees C and almost the same in both strains at 42 degrees C. The mutant had no obvious phenotype regarding its growth properties.