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PubMed2003

[Effect of soil water and fertilizer on soybean yield on loess slopeland].

Studies on the effect of soil water and fertilizer on soybean yield on loess slope farmland showed that soybean yield (Y) increased linearly with the increase of water use efficiency (WUE). Soybean yield and WUE increase with the increase of P fertilizer when P fertilizer was applied alone, but increased firstly and then decreased with the increase of N fertilizer when N fertilizer was applied alone. Therefore, N fertilizer should be applied with P fertilizer. Compared to no fertilizer, fertilizer could significantly increase soybean yield and WUE by 86.76%-470.16% and 69.64%-438.47%, respectively. A combined application of N and P fertilizers could increase more soybean yield and WUE than applied each of them alone, and the rational ratio of N and P (P2O5) was 1.3:1.

Crops, Agricultural↗
PubMed2004

[Impact of localized compaction and ridge fertilization on field nitrate transport and nitrate use efficiency].

The primary season of nitrate leaching in the Loess Plateau region is the monsoon, which is caused by heavy rainfall during the growth season of corn (Zea mays L.). Nitrate leaching to groundwater is an increasing concern in agriculture, and is one of the major nitrogen losing ways in dryland farming system. Localized compaction and ridge fertilization is a method for nitrogen fertilizer application, by which, less fertilizer leaching would occur. The NO3(-)-N transport in soil profile, corn yields and nitrogen use efficiency under localized compaction and ridge fertilization were investigated through two years field study. The factors that affect NO3(-)-N transport under localized compaction and ridge fertilization were studied, combined with simulated experiment. The results showed that NO3(-)-N was leached to below 90 cm in plat fertilization in the year of about 370 mm rainfall, a mean precipitation during the season, while the NO3(-)-N leakage of the fertilizer zone was reduced by localized compaction and ridge fertilization, as a result that the NO3(-)-N concentration below 60 cm was less than 10 mg.kg-1, and NO3(-)-N accumulated in 20-40 cm with a concentration 80-90 mg.kg-1. There was no significant difference in yield between application methods with 240.0 kg N.hm-2. However, the absorbed amount of nitrogen was improved significantly by localized compaction and ridge fertilization, and the nitrogen use efficiency was increased by 9%. The bulk density of the barriers had an evident effect on NO3(-)-N transport under localized compaction and ridge fertilization, but the effect of ridge slope was insignificant.

Biological Transport↗
PubMed2004

Fertility trend and pattern in a rural area of South Africa in the context of HIV/AIDS.

Little is known about the dynamics of fertility transition in South Africa, though recent studies have begun to shed light on demographic changes in the country. This study presents trends and patterns of fertility observed in a rural South African population. Various demographic and statistical techniques were used to examine fertility patterns in a population of 21,847 women in a rural KwaZulu-Natal (KZN) demographic surveillance area. These are compared with patterns seen in another South African rural population under demographic surveillance, and with data from the 1998 South Africa Demographic and Health Survey. Findings are interpreted in light of contraceptive use patterns and HIV prevalence in the population. In South Africa, the end of the fertility transition is now in sight. In rural KZN, where national fertility levels are highest, fertility has declined rapidly for about two decades and would have reached below replacement level in 2003. While fertility has declined rapidly among all women over age 18 years, fertility levels among adolescents have not changed in decades. Although most adolescents in rural KZN were sexually active (60%), few had ever used contraception (200%). High HIV seroprevalence appears to explain a small part of the fertility decline (12%); however, this effect is likely to grow in the near future as the HIV/AIDS epidemic continues in South Africa. If the current trends continue in the future, below replacement fertility, together with high mortality due to AIDS, it could soon lead to negative natural population growth in rural South Africa.

Adolescent↗
PubMed2004

[Study on the characteristic of assimilating nitrogenous phosphorous fertilizer and the accumulation disciplinarian of total tanshinons of Salvia miltiorrhiza].

OBJECTIVE: To confirm the amount of fertilizer and the ration of fertilizer. METHOD: Through the experiment of planting Salvia miltiorrhiza in pot and in field were carried out. RESULT: When N:P = 1:1, The production was 1.8 times more than the contrast group in plotting experiment, and in field the production of the highest fertilizer plot were 2.5 times more than the contrast and the higher and high fertilizer plot is 2.25 and 1.2 times respective were than those in the contrast group. CONCLUSION: The proper ration of nitrogenous fertilizer and phosphorous fertilizer is 1:1. Nitrogen shows negative effects to the accumulation of tanshinon IIA, the more the nitrogen ous fertilizer, The less the content of tanshinon IIA. In contrast, phosphor ous fertilizer shows good effects on the accumulation of tanshinon IIA. Phosphorous fertilizer could alleviate the decline of the content of tanshinon IIA by using nitrogenous fertilizer. The accumulation peak of the tanshinon IIA emerge in the period of 150 d.

Abietanes↗
PubMed2005

[Preliminary determination of organic pollutants in agricultural fertilizers].

Organic pollutants such as polycyclic aromatic hydrocarbons (PAHs) in agricultural fertilizers are new problem deserved more study. Eight kinds of organic pollutants including 43 compounds classified as US EPA priority pollutants in twenty one agricultural fertilizers which were universally used in China were determined by Gas chromatography-mass spectrum (GC-MS). Three kinds of organic pollutants including more than 5 compounds were detected in most fertilizers, composing mainly of phthalic acid esters (PAEs), nitrobenzenes (NBs) and polycyclic aromatic hydrocarbons (PAHs). There were 26 compounds detected in at least one fertilizer, five of them especially PAEs detected in most fertilizer and even in all fertilizers. Benzo(a)pyrene, a strongly carcinogenic compound was detected in two fertilizers. Higher concentrations of compounds were determined in those fertilizers such as multifunction compound fertilizers and coated fertilizers.

Crops, Agricultural↗
PubMed2006

[Clinical analysis of intracytoplasmic sperm injection in patients with previous fertilization failure after conventional IVF].

OBJECTIVE: To analyze the clinical outcome of intracytoplasmic sperm injection (ICSI) in patients with previous fertilization failure after conventional IVF. METHODS: Data from 20 ICSI cases (22 ICSI cycles) with previous complete failure of fertilization or with fertilization rate < or = 20% between January 2002 and December 2004 were retrospectively analyzed. The control group consisted of 100 consecutive ICSI cycles for male factor infertility in the same period. RESULTS: The fertilization rate dramatically increased from 5.4% after conventional IVF to 76.9% after ICSI treatment (chi-squared = 264.66, P < 0.001). However, the fertilization rate in the subgroup with previous low fertilization was significantly lower than those in the control and in the subgroup without previous fertilization (67.9% vs 77.5%, 67.9% vs 84.2%). Compared with the control group, the subgroup without previous fertilization had a higher pregnancy rate and implantation rate, but only the difference in the implantation rate was statistically significant (40.5% vs 18.9%). CONCLUSION: ICSI can overcome previous fertilization failure with conventional in vitro fertilization and thus improve the clinical outcome.

Adult↗
PubMed1978

The transition from natural to controlled fertility in Taiwan: a cross-sectional analysis of demand and supply factors.

Three factors are usually proposed as inducing the transition from natural to regulated fertility. Fertility regulation may occur when the demand for children is reduced; when general attitudes toward fertility regulaton become positive; and, finally, when such factors as infant and child survival prospects and natural fertility conditions improve. Applying the Easterlin framework for fertility determination, this paper considers the effect of these factors in the shift from natural to regulated fertility in Taiwan in 1965. Cross-sectional data for continuously married women aged 35-44 are used. The results indicate that, at the initial stages of the fertility transition, it is primarily an increase in the potential output of surviving children and a decline in the subjective costs associated with fertility regulation, rahter than a decline in desired fertility, that distinguish the natural fertility subpopulation from the regulating subpopulation.

Adult↗
PubMed1993

The spatial dynamics of U.S. fertility, 1970-1990.

"The fertility downturn in the U.S. since the baby boom has been accompanied by a growing divergence in regional fertility rates. This paper examines the spatial implications of recent fertility trends. Two interrelated questions are posed. First, how and why have the time trends in fertility varied spatially? Second, how have the regional patterns of fertility changed over time? These questions are investigated using a continuous spatio-temporal model of U.S. fertility built using the Dual Expansion Method. Results indicate that the pace of fertility decline has been the most rapid in the Northeast and the slowest in the West. Further, the traditional North-South distinctions in fertility rates are being replaced by East-West patterns. These changes tentatively suggest that regional ethnic composition is becoming an increasingly important factor in accounting for the spatial variation of U.S. fertility."

Americas↗
PubMed1981

[Childrearing environment and fertility in contemporary Japan (author's transl)].

This study focused on the decrease in the marital fertility rate and attempted to clarify some traits in childrearing behavior which are responsible for the low fertility. Regarding the increase in difficulties in childrearing, the author pointed out the necessity and possibility of fertility study from the viewpoint of childrearing. The author proposed to regard childbearing behavior as a part of childrearing behavior and to explain childbearing behavior by childrearing environment which surrounds the couple's childrearing behavior and childrearing consciousness. Childrearing environment is composed of family formation in the household, labor force status of the mother, housing conditions, nursery facilities, and physical environment in the community; these components are all closely allied. Data obtained from 2375 mothers with preschool children were studied. There were great differences in the degree of mother's participation in the labor foce but there was a large ratio of mothers who did not live with their parents and who wanted to work outside the home if nursery facilities could be affored. Clearly the desire of women of reproductive age to work is very strong and the differences in the labor force participation rate are the result of insufficient socialized child care. The authors found a stratum of women who were strongly orientated towards working but who had chosen to live with the parents as a solution to their child care problem. We could only find small differences in fertility by family formation in the household and by work history of mother when observed. However, when the 2 were combined, there were relatively large differences (1.94-2.65 after 10 years of marriage) which has rarely been observed in social analyses of fertility thus far. The lowest fertility by work history was observed among women who had worked since before their marriages, and the largest differences in fertility between 2 family formation types was found among these women (1.94:2.24). This difference in fertility can be supposed to reflect the difference in child care conditions by family formation in household. As to the reasons for limiting births, differences were not found between these 2 family formation types. Working mothers who relied upon their parents for child care expressed relatively greater anxiety about their child's development status than those mothers in nuclear families where child care was supplied by the nursery schools. It is likely that the trend of working mothers will not diminish, and we must thus anticipate the limit of the mechanism of maintaining the fertility by child care supplied by cohabiting parents. Physical environment in the community was found to be a factor in limiting childbirth and the effect was most conspicuous among women who had continued to work in the nuclear family.

Asia↗
PubMed1992

[Fertility preferences in Latin America: trends and differentials in seven countries].

The authors use Bongaarts's fertility preference measurement methodology to examine and compare changes in fertility preferences in Colombia, Costa Rica, the Dominican Republic, Ecuador, Jamaica, Peru, and Trinidad and Tobago over the period 1975-1989. "The trends of observed and desired fertility are examined at the national level and by level of education and rural-urban place of residence. The data used comes from fertility surveys....such as the World Fertility Survey (WFS) and the Demographic and Health Survey (DHS). The analysis suggests that the changes in fertility between the dates of the two surveys...are not due to changes in desired fertility, but mainly to differences in the degree to which fertility is controlled to coincide with desired levels.... Both the WFS and the DHS show that unwanted fertility was significant in all countries, specially in the lower socioeconomic strata." (SUMMARY IN ENG)

Americas↗
PubMed1998

Mode of fertilization and parental care in anurans

Current hypotheses for explaining which sex cares for offspring assume a relationship between the mode of fertilization and the sex showing parental care. In general, it is hypothesized that maternal care should be concentrated in taxa with internal fertilization, and paternal care should be concentrated in taxa with external fertilization. Studies have supported this relationship; however, new comparative techniques and new data on parental care and the frequency of internal fertilization in anurans suggest that the relationship should be re-evaluated. I examined the relationship between mode of fertilization and sex providing parental care in 334 taxa of anurans using concentrated changes tests and in 396 taxa of anurans using a method developed by Ridley (1983. The Explanation of Organic Diversity. The Comparative Method and Adaptations of Mating. Oxford: Clarendon). The results of the concentrated changes tests showed that both female and male parental care are randomly distributed among taxa with respect to mode of fertilization. However, using Ridley's method, I found significant relationships between mode of fertilization and sex providing parental care. The observed and expected numbers of transitions from external fertilization and no parental care to external fertilization and male parental care or to internal fertilization and female parental care are not qualitatively different. Therefore, the results of my analyses suggest that current hypotheses for explaining the occurrence of maternal versus paternal care in anurans should be reconsidered. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1989

Prediction of fertility of bovine semen: Preliminary studies with the hamster egg penetration test.

The ability of liposome-treated fresh and frozen spermatozoa from two bulls to interact with zona-free hamster oocytes was examined to show whether the in vitro test results would correspond with in vivo fertility as indicated by the 60 to 90 d nonreturn to service rates which, using frozen semen, were 77 and 59%, respectively. The motility of spermatozoa in washed suspensions was also rated. Hamster test results were obtained using three ejaculates from each bull both as fresh and frozen semen. The results with frozen semen corresponded with fertility. The averages of three hamster tests for oocyte penetration rates and mean number of spermatozoa per penetrated oocyte comparing spermatozoa from the bull with the higher fertility with spermatozoa from the bull with the lower fertility were 91% and 2.7 versus 56% and 1.4, respectively. Spermatozoa washed from frozen semen from the bull with the higher fertility interacted with hamster oocytes at the higher rate even when sperm motility was rated the same for both bulls. By contrast, fresh spermatozoa from the lower fertility bull interacted with hamster oocytes at a higher rate than spermatozoa from the higher fertility bull in six tests, comparing six ejaculates of fresh semen from both bulls. Comparing the higher fertility bull with the lower fertility bull, the average of six tests for oocyte penetration rates and mean number of spermatozoa per penetrated oocyte were 60% and 1.6 versus 89% and 3.0, respectively. This suggests that this hamster test cannot be used with fresh semen to predict relative levels of fertility of frozen semen. Also, the subjective rating of sperm motility did not correspond with the in vitro oocyte penetrating ability of the spermatozoa.

Journal Article↗
PubMed1995

In vitro maturation, fertilization and culture to blastocysts of bovine oocytes in protein-free media.

This study examined the role of protein supplementation at the various steps of the in vitro production of bovine embryos derived from two different morphological categories of COC. The basic medium was TCM 199 and was supplemented with hormones during maturation in vitro and either estrous cow serum (ECS), bovine serum albumin (BSA) at various concentrations or polyvinyl-alcohol (PVA). Fertilization in vitro was carried out using frozen-thawed semen or one bull in Fert-talp containing heparin, hypotaurin and epinephrine and either 6 mg/ml BSA or 1 mg/ml PVA. In vitro culture up to the blastocyst stage was performed in TCM 199 supplemented with either ECS, BSA or PVA. The first experiment investigated the influence of different medium-supplements (ECS, BSA or PVA) on nuclear maturation and revealed no significant differences among treatment groups nor between categories of COC (63.9% to 74.9% and 48.9% to 77.0%, respectively). The time course of in vitro fertilization was elucidated in Experiment 2 in medium supplemented with either protein or PVA during maturation and fertilization. Penetration was not affected (70.9% to 79.3% penetration 12 h after onset of oocyte-sperm-co-incubation), but formation of pronuclei was decreased (P < 0.05) 12 and 19 h after onset of oocyte-sperm-co-incubation and was retarded in medium supplemented with PVA (12 h: 63.8 vs 21.4 %; 19 h: 57.5 vs 20.8 %, respectively) while cleavage was not affected. In Experiment 3, six treatment groups were formed in which the two different morphological categories of cumulus-oocyte-complexes (COC) were incubated in basic medium supplemented with 1) ECS during maturation and embryo culture and BSA during fertilization; 2) PVA during maturation and embryo culture, fertilization medium with PVA; 3) PVA during maturation and embryo culture, fertilization medium with BSA; 4) BSA (1 mg/ml) during maturation, fertilization and embryo culture; 5) BSA (6 mg/ml) during maturation, fertilization and embryo culture; and 6) BSA (10 mg/ml) during maturation, fertilization and embryo culture. The rates of cleavage and the development to morulae or blastocysts did not differ (P > 0.05) among treatment groups and between both categories of COC and were showing a high degree of variability (cleavage 54.0% to 65.1% and 41.3% to 55.7%, respectively; morulae 25.3% to 53.0% and 26.0% to 51.2%, respectively; blastocysts 5.4% to 24.7% and 0.6% to 20.3%, respectively). Parthenogenetic activation only rarely occurred in medium containing PVA throughout all steps of in vitro production of bovine embryos (Experiment 4) and led to early cleavage stages (8%), but no development to morula- or blastocyst-stages was observed. It is concluded that 1) formation of pronuclei was retarded in medium lacking protein-supplementation, indicating that BSA is required for regular fertilization in vitro and 2) under our experimental conditions, protein-supplementation is not necessary for maturation and development up to the blastocyst stage in vitro.

Journal Article↗
PubMed1996

In vitro maturation and fertilization of equine oocytes recovered during the breeding season.

The aim of this study was to develope an efficient and reproducible procedure for in vitro maturation (IVM) and fertilization (IVF) in the horse. Cumulus-oocyte complexes (COCs) recovered from the ovaries of mares slaughtered during the breeding season were morphologically evaluated, and those showing a compact cumulus and homogeneously appearing cytoplasm were selected for culture. Effects on the maturation of estrous mare serum (EMS) versus estrous cow serum (ECS) as medium supplement were also evaluated (Experiment 1). In Experiment 2, the fertilization of in vitro matured oocytes with frozen-thawed semen separated by swim-up and treated with heparin was carried out to determine the effects on fertilization of 1) increasing sperm concentrations (1x 10(6), 5 x 10(6) and 1 x 10(7)sperm cells/ml), 2) IVM medium supplementation with EMS or ECS and 3) partial cumulus mass removal before insemination. Forty-nine percent of the collected oocytes (335 683 ) showed a compact cumulus and homogeneous ooplasm and thus were selected for culture. In Experiment 1, high nuclear maturation rates were observed in both EMS (82%,32 39 ) and ECS (87.5%,56 64 ) groups, with no statistically significant difference. In Experiment 2, the percentage of normal fertilization (2 polar bodies, 2 pronuclei and sperm tail) was similar for all 3 tested sperm concentrations (12.9%,4 31 ; 15.2%,9 59 and 15.5%,9 58 ). No advantage in using the homologous serum in IVM medium was noted in terms of fertilization (12.2%, 5 41 with EMS vs 12.9%, 4 31 for ECS). However, significantly higher fertilization rates were obtained after partial cumulus removal compared with that of oocytes fertilized with a whole cumulus (32.6%, 14 43 vs 12.2%, 5 41 ; P < 0.05). The incidence of polyspermic fertilization was low under all culture conditions (0 to 2.4%). In a replicate in which the oocytes fertilized after the cumulus removal were further cultured for 72 h two embryos, one at the 2-cell stage and the other at the 4-cell stage, could be obtained. These results indicate that, in the horse, the cumulus can be partially removed to increase the fertilization of compact-cumulus oocytes recovered during the breeding season using frozen-thawed, heparin-treated semen.

Journal Article↗
PubMed1996

A comparative study on developmental capacity to blastocysts derived from 1-and 2(3)-cell bovine embryos after in vitro maturation and fertilization.

The present study was conducted to compare the developmental capacity of 1-and 2(3)-cell embryos after 18 and 30 h of fertilization, and blastocyst cell number and in vitro survival after freezing and thawing of bovine blastocysts derived from the 1-and 2-cell embryos. Oocytes were matured and fertilized by conventional IVM/IVF methods. After 18 or 30 h of fertilization, 1-cell embryos (18 h-fertilization) or 1- and 2(3)-cell embryos (30 h-fertilization) were cultured for 8 or 10 d in synthetic oviduct fluid medium (SOFM) supplemented with 10% human serum (HS), minimum essential medium (MEM) essential or nonessential amino acids and glutamine. The separate culture of 1- and 2(3)-cell embryos after 30 h of fertilization showed higher (p < 0.01) cleavage, development to expanded and hatched blastocysts than culture of 1-cell embryos after 18 h of fertilization. Two-cell embryos of 30 h-fertilization group had higher developmental capacity to expanded and hatched blastocysts than 1-cell embryos at 18 or 30 h after insemination (Experiment I). However, there was no significant difference in the mean cell number of blastocysts derived from the culture of 1-cell and 2(3)-cell embryos, respectively (Experiment II). The in vitro survival or hatching after freezing and thawing of blastocysts was significantly affected by embryonic quality before freezing, but did not significantly differ with blastocysts derived from 1- and 2(3)-cell embryos after 18 or 30 h of fertilization. The results indicate that the culture of 2(3)-cell embryos after 30 h of fertilization is an effective method to produce more transferable embryos (blastocysts) in bovine IVM, IVF and IVC techniques.

Journal Article↗
PubMed2006

Successful pregnancy after ICSI with strontium oocyte activation in low rates of fertilization.

Fertilization failure (complete fertilization failure or low fertilization rates) after intracytoplasmic sperm injection (ICSI) can occur in rare cases. In the majority of these cases, the unfertilized oocytes are inactivated. Assisted oocyte activation was applied as a treatment option for a case of low fertilization rate as a clinical trial. A patient with a low fertilization rate (ranging from 0% to 33.3%; mean = 17.0%) after eight previous ICSI cycles at another hospital, was diagnosed with fertilization failure. The most likely cause of fertilization failure was failure of oocyte activation. Therefore, artificial oocyte activation by strontium treatment was combined with ICSI to achieve viable fertilized oocytes. Oocytes were stimulated with strontium (10 mM SrCl(2), 60 min) approximately 30 min after ICSl. Six injected oocytes were stimulated and all were then successfully fertilized. Two blastocysts were transferred into the uterus, resulting in a pregnancy and birth. A second pregnancy was achieved following implantation of two cryopreserved embryos (one blastocyst and one morula). In conclusion, strontium treatment was found to be an effective method for artificial oocyte activation in a case with a low fertilization rate after ICSI.

Adult↗
PubMed2000

In vitro fertilization and intracytoplasmic sperm injection for couples with unexplained infertility after failed direct intraperitoneal insemination.

PURPOSE: The objective was to determine the optimal insemination technique in patients undergoing in vitro fertilization (IVF) after failed direct intraperitoneal insemination (DIPI) and the outcome of intracytoplasmic sperm injection (ICSI) in such cases. METHODS: In case-control studies, 53 couples with unexplained infertility who underwent IVF after four failed DIPI cycles were compared with 75 couples with tubal or endometriosis infertility as controls. Thirty couples with unexplained infertility after failing to conceive with DIPI and conventional IVF who underwent ICSI and 58 couples with male-factor infertility as controls also were compared. Fertilization cleavage, embryo quality, implantation, and pregnancy were compared after IVF and after ICSI. RESULTS: There was a significant difference in fertilization rates after IVF between cases of unexplained infertility after failing to conceive with DIPI (40.4%) and patients with tubal or endometriosis infertility (67.9%). There also was a significant difference in total fertilization failure rates between the two groups (30.4% and 3.9%, respectively). There was a slight but significant difference in numbers of fertilized oocytes after ICSI between patients with low fertilization rate undergoing IVF after failing to conceive DIPI (85.8%) and patients with male factor (90.4%). Total fertilization failure was not observed in these cases. CONCLUSIONS: Couples with unexplained infertility after failing to conceive with DIPI show a failed fertilization or a low fertilization rate after IVF. However, they demonstrated a good chance of becoming pregnant after subsequent ICSI, even with statistically significant difference in fertilization rate as compared with male-factor cases.

Adult↗
PubMed1971

ColB2-K77, a fertility-repressed F-like factor.

The colicinogenic B factor, transferred from Escherichia coli strain K77 (and termed ColB2-K77 or ColB2) to an E. coli K12 F(-) strain, is capable of promoting its own transfer to other K12 F(-) strains at a low rate (from LFC cultures) which can be increased under special conditions (HFC cultures). LFC cultures of K12 (ColB2)(+) F(-) strains show a low level of adsorption of F-specific phage particles which also increases under HFC conditions. The ColB2 factor is thus inferred to be an F-like sex factor which is repressed in its fertility. This repression is concluded to be due to a cytoplasmic repressor since, when ColB2 is present in cells containing an F factor (either autonomous or integrated), F fertility is also repressed as shown by the inability of such (ColB2)(+)F(+) [or (ColB2)(+)Hfr] strains to plaque F-specific phages, and by a reduction in the level of chromosomal transfer from such strains, compared to the corresponding F(+) (or Hfr) control strains. Mutants of the ColB2 factor in which fertility is no longer repressed (fertility derepressed or Fdr mutants) have been isolated. The ColB2Fdr mutant strains do not appear to be able to mobilize chromosomal transfer, although they have acquired F-specific phage sensitivity demonstrable by plaque formation and they transfer their colicin factor at high frequency and are well piliated. The Fdr mutation is presumed to result in the inability to synthesize the cytoplasmic fertility repressor since the ColB2Fdr factor does not repress the fertility of an F factor when present in the same host strain. A fertility-repressed drug resistance factor of the R(f) type is not stable in the presence of a ColB2 factor in the same cell and is eliminated in about 10% of the cells per generation. In contrast, another factor characteristic of the R(i) type is fully compatible with ColB2. Under conditions artificially stabilizing (ColB2Fdr)(+) (Rf)(+) strains, the enhanced fertility of ColB2Fdr is not repressed by the presence of the R factor, nor does the presence of R(f) in the intermediate strain of an HFC (for ColB2) system inhibit the normal increase in ColB2 transmissibility. It is concluded that the repressors of R(f) and ColB2, although both active on F fertility, are different; this may indicate that at least two independently repressible cistrons are involved in the expression of fertility characteristics.

Adsorption↗