posted on 2018-03-09, 00:00authored byGuotao Peng, Robbie M. Martin, Stephen P. Dearth, Xiaocun Sun, Gregory L. Boyer, Shawn R. Campagna, Sijie Lin, Steven W. Wilhelm
Freshwater
cyanobacterial blooms are regularly formed by Microcystis spp., which are well-known producers of the
hepatotoxin microcystin. The environmental factors that regulate microcystin
synthesis remain unclear. We used reverse transcription-quantitative
PCR (RT-qPCR), metabolomics, and toxin profiling (both by LC-MS) to
measure the response of Microcystis aeruginosa NIES-843
to nitrogen (N) concentration, N chemistry (nitrate versus urea),
and a range of seasonally relevant temperatures. Growth rates at lower
temperatures were slower but resulted in increased cellular microcystin
content (quota), and at these lower temperatures, N concentration
had no effect on toxin production. In contrast, at warmer temperatures,
reduction in N concentration increased toxin production, especially
when urea was supplied as the nitrogen source. Our culture results
demonstrate how temperature may lead to physiological responses ranging
from slow growing yet very toxic cells at cool temperatures, to faster
growing but less-toxic cells at warmer temperatures. This response
represents a key interaction in bloom dynamics. Capturing this phenomenon
as a temperature-driven toxin phenotype incorporated into models might
improve the ability to predict microcystin biosynthesis during cyanobacterial
blooms.