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11.
Nutrient limitation conditions, optimization and comparison of polyhydroxyalkanoate (PHA) yields and biomass production by parent and mutant strains of Rhizobium meliloti were investigated. Complex interactions among concentrations of sucrose (5–55 g/l), urea (0.05–0.65 g/l) inoculum (10–250 ml/l) and K2HPO4 (0.5–2 g/l), were studied using central composite rotatable design (CCRD) experiments. Phosphate-limiting medium (0.33 g K2HPO4/l) in the presence of excess carbon (sucrose 42.5 g/l) results in more production of PHA (2.2 g/l) in the parent strain. In comparison, the mutant strain required moderate levels of sucrose (30 g/l), along with excess of phosphate (1 g/l) for high PHA content of cell biomass (80%) and PHA yield (3.3 g/l). Optimised PHA production (biomass 4.8 g/l and PHA 3.09 g/l) by the parent strain occurred at: sucrose 51.58 g/l, urea 0.65 g/l, K2HPO4 0.48 g/l and inoculum 10 ml/l. In the mutant strain, higher yields of biomass (9.05 g/l) and PHA (5.66 g/l) were obtained in Optimised medium containing: sucrose 55 g/l, urea 0.65 g/l, K2HPO4 1.0 g/l and inoculum 150.58 ml/l. 相似文献
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On the relevance of using laboratory selection to study the adaptive value of circadian clocks
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The phrase ‘as sure as night comes after day’ highlights the most conspicuous phenomenon on earth (i.e. the daily cycling of geophysical factors). It is hypothesized that life‐forms on earth have evolved timekeeping mechanisms (circadian clocks) as adaptations to cope with such cyclic variations in their environment and, to test this hypothesis, diverse strategies have been employed. In this review, these different approaches, including comparative, clinal, ecology and/or trait manipulation and laboratory selection strategies are discussed, aiming to evaluate the adaptive value of circadian clocks. The limitations of each of these methods are assessed, and it is suggested that laboratory selection is an ideal, potent and suitable strategy for examining whether circadian clocks are indeed adaptations. In support of this, laboratory selection strategies are highlighted and critically reviewed in a discussion of studies that demonstrate the evolution of circadian clocks and life‐history traits in response to selection for the timing of rhythmic behaviours, as well as those studies that demonstrate the evolution of circadian clocks in response to selection for life‐history traits. Finally, newer approaches are proposed that involve the use of mutants, simultaneous manipulation of multiple environmental factors and genomic technologies in conjunction with laboratory selection to further explore the adaptive significance of circadian clocks. 相似文献
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Roberta Diavana De Souza Alinne Ulbrich Mores Laura Cavalca Rosimeire Takaki Rosa Lakshman Perera Samaranayake Edvaldo Antonio Ribeiro Rosa 《Gerodontology》2009,26(2):157-161
Background: The virulence potential of Candida albicans strains enrolled in denture‐related candidosis still remains uncertain. Candida albicans cells with higher cell surface hydrophobicity (CSH) rates, so‐called hydrophobic, present higher adhesion success in different host tissues than cells with lower rates, or even hydrophilic. Objective: The proposition of this study was to evaluate the differences in the CSH of strains isolated from denture users with and without denture‐related candidosis. Material and methods: The strains were obtained from two paired groups of patients living a same retirement house. Fungal cells were submitted to CSH evaluation by the hydrocarbon partition test using xylene. Results: The measures revealed that the yeasts from patients with candidosis had CSH values ranging from 4.52% to 12.24%, with an average of 8.22 ± 2.92%. In the countergroup, the CSH ranged from 3.86% to 14.36%, with an average of 8.38 ± 3.76%. The difference between the groups were considered not relevant (p = 0.997). Conclusion: The results let to the inference that natural populations of C. albicans from patients with and without clinical manifestation denture‐related candidosis do not differ one from the other regarding to CSH. 相似文献
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Susan L. F. Meyer Inga A. Zasada Daniel P. Roberts Bryan T. Vinyard Dilip K. Lakshman Jae-Kook Lee David J. Chitwood Lynn K. Carta 《Journal of nematology》2006,38(3):333-338
Extracts from the plants Plantago lanceolata and P. rugelii were evaluated for toxicity to the root-knot nematode Meloidogyne incognita, the beneficial microbes Enterobacter cloacae, Pseudomonas fluorescens and Trichoderma virens, and the plant-pathogenic fungi Fusarium oxysporum f. sp. gladioli, Phytophthora capsici, Pythium ultimum, and Rhizoctonia solani. Wild plants were collected, roots were excised from shoots, and the plant parts were dried and ground to a powder. One set of extracts (10% w/v) was prepared in water and another in methanol. Treatments included extract concentrations of 25%, 50%, 75% and 100%, and water controls. Meloidogyne incognita egg hatch was recorded after 7-day exposure to the treatments, and second-stage juvenile (J2) activity after 48 hours. All extracts were toxic to eggs and J2, with P. lanceolata shoot extract tending to have the most activity against M. incognita. Numbers of active J2 remained the same or decreased in a 24-hour water rinse following the 48-hour extract treatment, indicating that the extracts were lethal. When data from water- and methanol-extracted roots and shoots of both plant species were combined for analysis, J2 tended to be more sensitive than eggs to the toxic compounds at lower concentrations, while the higher concentrations (75% and 100%) were equally toxic to both life stages. The effective concentrations causing 50% reduction (EC50) in egg hatch and in J2 viability were 44.4% and 43.7%, respectively. No extract was toxic to any of the bacteria or fungi in our assays. 相似文献
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Fernanda?Brasil?Baboni Dayton?Barp Ana?Claudia?Santos?de?Azevedo Izidoro Lakshman?Perera?Samaranayake Edvaldo?Antonio?Ribeiro?RosaEmail author 《Mycopathologia》2009,168(5):227-235
The habit of cigarette smoking is associated with higher oral candidal carriage and possible predisposition to oral candidosis.
The effects of exposure to smoke on the virulence properties of oral yeasts remain obscure. Hence, we showed in vitro the
effect of cigarette smoke condensate (CSC) on ten clinical isolates of Candida albicans obtained from nonsmoking volunteers, as well the type-strain CBS562. CSC was generated by complete burn of five commercial
cigarettes in an in-house smoking machine and used to prepare the culture broth in which the strains were grown. In 24-h intervals
(T24, T48, and T72), the cells were harvested, washed, subcultured, and the resultant growth were evaluated for possible variations for secreted
aspartyl protease, phospholipase, chondroitinase, and hemolysins, adhesion to acrylic and cell surface hydrophobicity (CSH).
The results indicated a temporal increase in the secretion rates of enzymes, particularly when yeast cells were exposed to
CSC for 48–72 h (P < 0.05). Similarly, adhesion to acrylic and CSH increased with exposure period (P < 0.05). Based on foregoing, we concluded that CSC may promote significant enhance in the secretion of candidal histolytic
enzymes and adherence to denture surfaces, thereby promoting oral yeast carriage and possible infection. 相似文献
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Lakshman PL Tachibana S Toyama H Taira T Suganuma T Suntornsuk W Yasuda M 《Journal of industrial microbiology & biotechnology》2011,38(9):1485-1492
An acid proteinase from Monascus purpureus No. 3403, MpuAP, was previously purified and some characterized in our laboratory (Agric Biol Chem 48:1637–1639, 1984). However, further information about this enzyme is lacking. In this study, we investigated MpuAP’s comprehensive substrate
specificity, storage stability, and prospects for reducing antigenicity of whey proteins for application in the food industry.
MpuAP hydrolyzed primarily five peptide bonds, Gln4–His5, His10–Leu11, Ala14–Leu15, Gly23–Phe24 and Phe24–Phe25 in the oxidized insulin B-chain. The lyophilized form of the enzyme was well preserved at 30–40°C for 7 days without stabilizers.
To investigate the possibility of reducing the antigenicity of the milk whey protein, enzymatic hydrolysates of the whey protein
were evaluated by inhibition ELISA. Out of the three main components of whey protein, casein and α-lactalbumin were efficiently
degraded by MpuAP. The sequential reaction of MpuAP and trypsin against the whey protein successfully degraded casein, α-lactalbumin
and β-lactoglobulin with the highest degree of hydrolysis. As a result, the hydrolysates obtained by using the MpuAP–trypsin
combination showed the lowest antigenicity compared with the single application of pepsin, trypsin or pepsin–trypsin combination.
Therefore, the overall result suggested that the storage-stable MpuAP and trypsin combination will be a productive approach
for making hypoallergic bovine milk whey protein hydrolysates. 相似文献