Highly selective isolation and characterization of Lipomyces starkeyi mutants with increased production of triacylglycerol.

The oleaginous yeast Lipomyces starkeyi is an attractive organism for the industrial production of lipids; however, the amount of lipid produced by wild-type L. starkeyi is insufficient. The study aims to obtain L. starkeyi mutants that rapidly accumulate large amounts of triacylglycerol (TAG). Mutagenized yeast cells at the early stages of cultivation were subjected to Percoll density gradient centrifugation; cells with increased production of TAG were expected to be enriched in the resultant upper fraction because of their lower density. Among 120 candidates from the upper fractions, five mutants were isolated that accumulated higher amounts of TAG. Moreover, when omitting cells with mucoid colony morphology, 11 objective mutants from 11 candidates from the upper fraction were effectively (100%) isolated. Of total 16 mutants obtained, detailed characterization of five mutants was performed to reveal that five mutants achieved about 1.5-2.0 times TAG concentration (4.7-6.0 g/L) as compared with the wild-type strain (3.6 g/L) at day 5. Among these five mutants, strain E15 was the best for industrial use because only strain E15 showed significantly higher TAG concentration as well as significantly higher degree of lipid to glucose and biomass to glucose yields than the wild-type strain. Thus, Percoll density gradient centrifugation is an effective method to isolate mutant cells that rapidly accumulate large amounts of TAG. It is expected that by repeating this procedure as part of a yeast-breeding program, L. starkeyi mutants suitable for industrial lipid production can be easily and effectively obtained.

[Factors associated with smoking continuation or cessation in men upon learning of their partner's pregnancy].

OBJECTIVES: Factors associated with smoking continuation or cessation were analyzed among parents of 4-month-old infants, in order to prepare the basic materials for a smoking cessation support program for pregnant women and their partners. The study focused on the changes in partners' smoking activities upon learning of their partner's pregnancy. METHODS: An anonymous self-completed questionnaire was given to parents of 1,198 infants during a 4-month medical checkup in City A of Hyogo prefecture (776 couples) and City B of Gifu prefecture (422 couples). The questionnaire items collected information on age, education, smoking history, current smoking status, and awareness about smoking. The additional items for fathers were occupation, workplace smoking environment, and attitude toward smoking; and the additional items for women were number of children, family composition, and partners' attitudes and behaviors regarding smoking upon learning of their pregnancy. The number of valid answers (for pairs) was 558 (71.9%) in City A and 395 (93.6%) in City B. The data on men who had been smokers before learning of their partner's pregnancy were analyzed. For each area, a comparative item-by-item analysis was performed on data from men who ceased smoking upon learning of the pregnancy (smoking cessation group) and those who continued smoking (smoking continuation group). For logistic regression analysis, the objective variables were the 2 groups, and the explanatory variables were the items showing statistical differences between the groups and the items related to the survey areas. RESULTS: Of the men whose data were included in the analysis, 210 (37.6%) in City A and 204 (51.6%) in City B had been smokers before learning of their partner's pregnancy. Among these, 16 (7.6%) in City A and 26 (12.7%) in City B ceased smoking after learning of the pregnancy. The results of logistic regression analysis showed that the odds ratio for continuing smoking was 2.77 [95% confidence interval (CI): 1.17-6.57] for men with at least 2 children, 0.05 (95% CI: 0.01-0.18) for those who decided to cease smoking immediately, and 0.19 (95% CI: 0.08-0.44) for those who were strongly encouraged to cease smoking by their pregnant partner upon learning of the pregnancy. CONCLUSION: In male smokers who learned of their partner's pregnancy, men with 2 or more children were more likely to continue smoking, while men who considered quitting smoking immediately upon learning of the women's pregnancy, and those whose pregnant partners strongly encouraged them to do so, were more likely to cease smoking.