The mixotrophic dinoflagellate Dinophysis acuminata is a widely distributed diarrhetic shellfish poisoning (DSP) producer. Toxin variability of Dinophysis spp. has been well studied, but little is known of the manner in which toxin production is regulated throughout the cell cycle in these species, in part due to their mixotrophic characteristics. Therefore, an experiment was conducted to investigate cell cycle regulation of growth, photosynthetic efficiency, and toxin production in D. acuminata . First, a three-step synchronization approach, termed “starvation-feeding-dark”, was used to achieve a high degree of synchrony of Dinophysis cells by starving the cells for 2 weeks, feeding them once, and then placing them in darkness for 58 h. The synchronized cells started DNA synthesis (S phase) 10 h after being released into the light, initiated G2 growth stage eight hours later, and completed mitosis (M phase) 2 h before lights were turned on. The toxin content of three dominant toxins, okadaic acid (OA), dinophysistoxin-1 (DTX1) and pectenotoxin-2 (PTX2), followed a common pattern of increasing in G1 phase, decreasing on entry into the S phase, then increasing again in S phase and decreasing in M phase during the diel cell cycle. Specific toxin production rates were positive throughout the G1 and S phases, but negative during the transition from G1 to S phase and late in M phase, the latter reflecting cell division. All toxins were initially induced by the light and positively correlated with the percentage of cells in S phase, indicating that biosynthesis of Dinophysis toxins might be under circadian regulation and be most active during DNA synthesis.
Jun Huang,Yaoyao Su,Xiaoman Chen,Gang Yang,Zhirong Wang,Kewei Chen,Muying Du,Zsolt Zalán,Ferenc Hegyi,Jianquan Kan
Sterigmatocystin (STC), a mycotoxin that pollutes wheat and other grains and is related to health risks, has attracted increasing attention. In this study, we have explored the toxicity conditions of Aspergillus versicolor in wheat and identified a potential biological control method. By constructing a water activity (Aw)-water content curve, the effects of temperature, Aw, and culture time on toxin production by A . versicolor in wheat were determined. The Aw was found to be 0.96, and the concentration of STC in wheat reached the maximum (105.7 mg/kg) after 10 d of culture at 28 °C. Biocontrol bacteria were screened using plate confrontation, agar diffusion, and co-culture in wheat. The results showed that Bacillus subtilis HJ4 has significant antifungal activity against A. versicolor in vitro and in vivo . In vivo experiments showed that B. subtilis HJ4 significantly reduced the toxicity of A. versicolor to wheat (51%) on day-7, but the control effect was weakened (10%) on day-20. Finally, research on the antifungal mechanism of B. subtilis HJ4 revealed that its action primarily relies on competition for space and nutrients, destroying the cellular structure of the fungus and secreting substances with antifungal activity, such as proteins, cyclic lipopeptides, and oligosaccharides, aiding in control against A. versicolor . In summary, this study has emphasized the influence of environmental factors on the growth and toxin production of A. versicolor in wheat and evaluated the potential of B. subtilis HJ4 in reducing the pollution caused by A. versicolor and STC in wheat.
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