BackgroundCaffeine is one of the most abundant methylxanthines in tea, and it remains stable in processing of general teas. In the secondary metabolism of microorganism, theophylline is the main conversion product in caffeine catabolism through demethylation. Microorganisms, involved in the solid-state fermentation of pu-erh tea, have a certain impact on caffeine level. Inoculating an appropriate starter strain that is able to convert caffeine to theophylline would be an alternative way to obtain theophylline in tea. The purpose of this study was to isolate and identify the effective strain converting caffeine to theophylline in pu-erh tea, and discuss the optimal conditions for theophylline production.ResultsCaffeine content was decreased significantly (p < 0.05) and theophylline content was increased significantly (p < 0.05) during the aerobic fermentation of pu-erh tea. Five dominant fungi were isolated from the aerobic fermentation and identified as Aspergillus niger, Aspergillus sydowii, Aspergillus pallidofulvus, Aspergillus sesamicola and Penicillium mangini, respectively. Especially, A. pallidofulvus, A. sesamicola and P. mangini were detected in pu-erh tea for the first time. All isolates except A. sydowii TET-2, enhanced caffeine content and had no significant influence on theophylline content. In the aerobic fermentation of A. sydowii TET-2, 28.8 mg/g of caffeine was degraded, 93.18% of degraded caffeine was converted to theophylline, and 24.60 mg/g of theophylline was produced. A. sydowii PET-2 could convert caffeine to theophylline significantly, and had application potential in the production of theophylline. The optimum conditions of theophylline production in the aerobic fermentation were 1) initial moisture content of 35% (w/w), 2) inoculation quantity of 8%, and 3) incubation temperature at 35 °C.ConclusionsFor the first time, we find that A. sydowii PET-2 could convert caffeine to theophylline, and has the potential value in theophylline production through aerobic fermentation.
The level of docosahexaenoic acid is efficiently improved by FO lipid emulsions. The changes observed in eicosapentaenoic acid and arachidonic acid, and the associated safety issue, however, remain to be clarified. Any clinical benefit or detrimental effect of using FO in premature neonates cannot be demonstrated by the present study.
The dissemination of plasmid-borne
antibiotic resistance genes
(ARGs) in wastewater is becoming an urgent concern. Previous studies
mainly focused on the effects of coexisting contaminants on plasmid
conjugation, but ignored the potential contribution of some byproducts
inevitably released from wastewater treatment processes. Herein, we
demonstrate for the first time that nitric oxide (NO), an intermediate
of the wastewater nitrogen cycle, can significantly boost the conjugative
transfer of plasmid RP4 from Escherichia coli K12 to different recipients (E. coli HB101, Salmonella typhimurium, and
wastewater microbiota). Phenotypic and genotypic tests confirmed that
NO-induced promotion was not attributed to the SOS response, a well-recognized
driver for horizontal gene transfer. Instead, NO exposure increased
the outer membrane permeability of both the donor and recipient by
inhibiting the expression of key genes involved in lipopolysaccharide
biosynthesis (such as waaJ), thereby lowering the
membrane barrier for conjugation. On the other hand, NO exposure not
only resulted in the accumulation of intracellular tryptophan but
also triggered the deficiency of intracellular methionine, both of
which were validated to play key roles in regulating the global regulatory
genes (korA, korB, and trbA) of plasmid RP4, activating its encoding transfer apparatus (represented
by trfAp and trbBp). Overall, our
findings highlighted the risks of NO in spreading ARGs among wastewater
microbiota and updated the regulation mechanism of plasmid conjugation.
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