Simulated upwelling and marine heatwave events promote similar growth rates but differential domoic acid toxicity in Pseudo-nitzschia australis.

Along the west coast of the United States, highly toxic Pseudo-nitzschia blooms have been associated with two contrasting regional phenomena: seasonal upwelling and marine heatwaves. While upwelling delivers cool water rich in pCO2 and an abundance of macronutrients to the upper water column, marine heatwaves instead lead to warmer surface waters, low pCO2, and reduced nutrient availability. Understanding Pseudo-nitzschia dynamics under these two conditions is important for bloom forecasting and coastal management, yet the mechanisms driving toxic bloom formation during contrasting upwelling vs. heatwave conditions remain poorly understood. To gain a better understanding of what drives Pseudo-nitzschia australis growth and toxicity during these events, multiple-driver scenario or 'cluster' experiments were conducted using temperature, pCO2, and nutrient levels reflecting conditions during upwelling (13 °C, 900 ppm pCO2, replete nutrients) and two intensities of marine heatwaves (19 °C or 20.5 °C, 250 ppm pCO2, reduced macronutrients). While P. australis grew equally well under both heatwave and upwelling conditions, similar to what has been observed in the natural environment, cells were only toxic in the upwelling treatment. We also conducted single-driver experiments to gain a mechanistic understanding of which drivers most impact P. australis growth and toxicity. These experiments indicated that nitrogen concentration and N:P ratio were likely the drivers that most influenced domoic acid production, while the impacts of temperature or pCO2 concentration were less pronounced. Together, these experiments may help to provide both mechanistic and holistic perspectives on toxic P. australis blooms in the dynamic and changing coastal ocean, where cells interact simultaneously with multiple altered environmental variables.

Screening the PRISM Library against Staphylococcus aureus Reveals a Sesquiterpene Lactone from Liriodendron tulipifera with Inhibitory Activity.

Infections caused by the bacterium Staphylococcus aureus continue to pose threats to human health and put a financial burden on the healthcare system. The overuse of antibiotics has contributed to mutations leading to the emergence of methicillin-resistant S. aureus, and there is a critical need for the discovery and development of new antibiotics to evade drug-resistant bacteria. Medicinal plants have shown promise as sources of new small-molecule therapeutics with potential uses against pathogenic infections. The principal Rhode Island secondary metabolite (PRISM) library is a botanical extract library generated from specimens in the URI Youngken Medicinal Garden by upper-division undergraduate students. PRISM extracts were screened for activity against strains of methicillin-susceptible S. aureus (MSSA). An extract generated from the tulip tree (Liriodendron tulipifera) demonstrated growth inhibition against MSSA, and a bioassay-guided approach identified a sesquiterpene lactone, laurenobiolide, as the active constituent. Intriguingly, its isomers, tulipinolide and epi-tulipinolide, lacked potent activity against MSSA. Laurenobiolide also proved to be more potent against MSSA than the structurally similar sesquiterpene lactones, costunolide and dehydrocostus lactone. Laurenobiolide was the most abundant in the twig bark of the tulip tree, supporting the twig bark's historical and cultural usage in poultices and teas.