Intra- and interspecies differences in growth and toxicity of Pseudo-nitzschia while using different nitrogen sources

Abstract

Clonal cultures of plankton are widely used in laboratory experiments and have contributed greatly to knowledge of microbial systems. However, many physiological characteristics vary drastically between strains of the same species, calling into question our ability to make ecologically relevant inferences about populations based on studying one or a few strains. This study included nineteen non-axenic strains of three species of the diatom Pseudo-nitzschia isolated primarily from the mid-Atlantic coastal region of the United States.Toxin (domoic acid) production and growth rates were measured in cultures using different nitrogen sources (NH 4 + , NO 3 ⎯ and urea) and growth irradiances. The strains exhibited broad differences in growth rate and toxin content even between strains isolated from the same water sample. The influence of bacteria on toxin production was not investigated. Both P. multiseries clones produced toxin, yet preferentially used different nitrogen sources. Only two out of nine P. calliantha and two out of five P. fraudulenta isolates were toxic and domoic acid content varied by orders of magnitude. All three species had variable intraspecies growth rates on each nitrogen source, but P. fraudulenta strains had the broadest range. Light-limited growth rate and maximum growth rate in P. fraudulenta and P. multiseries varied with species. These findings show the importance of defining intra-and interspecies variability in ecophysiology and toxicity.Ecologically relevant functional diversity in the form of ecotypes or cryptic species appears to be present in the genus Pseudo-nitzschia.

Species occurrence of the potentially toxigenic diatom genus Pseudo-nitzschia and the associated neurotoxin domoic acid in the Argentine Sea

“…The DA cell quotas estimated from the two samples in which DA was detected together with a predominance of P. fraudulenta (% 98% of total Pseudo-nitzschia) were 0.002 and 0.120 pg cell À1 . These values are comparable to DA cell quotas obtained in cultures of P. fraudulenta by Rhodes et al (1998a,b) (maximum 0.03 pg cell À1 ) and Thessen et al (2009) (maximum 0.16 pg cell À1 ). Despite these low toxin levels, DA has been previously detected in phytoplankton net samples (up to 6.6 mg L À1 ) collected in San José Gulf and Nuevo Gulf, coinciding with high cell densities of P. fraudulenta (Sastre et al, 2007).…”

“…Rhodes et al, 1996;Villac et al, 1993;Thessen et al, 2009;Sahraoui et al, 2011). Environmental factors, such as ambient nutrient concentrations, temperature, salinity, irradiance, photoperiod and pH, have been known to influence and under some circumstances to induce DA production in laboratory culture experiments (Lelong et al, 2012;and references therein).…”

Induction of domoic acid production in the toxic diatom Pseudo-nitzschia seriata by calanoid copepods

“…This indicates that actively dividing cells were producing increasing amounts of DA. This is contrary to the findings of most earlier studies which showed that the highest DA levels occured during the stationary growth phase, when cell division ceased (reviewed in Bates, 1998;Fehling et al, 2004;Thessen et al, 2009). Garrison et al (1992) reported that P. australis produced DA during the exponential phase, but concluded that the results could be biased due to the very dense starting inoculum, which might have stressed the algae and, hence, enhanced DA production.…”

Pseudo-nitzschia physiological ecology, phylogeny, toxicity, monitoring and impacts on ecosystem health

“…Other studies also have observed measurable levels of DA prior to the onset of stationary growth, e.g. in P. australis (Garrison et al, 1992), P. multiseries (Pan et al, 1996a;Radan, 2008;Thessen et al, 2009) and P. fraudulenta (Thessen et al, 2009). P. cuspidata even exhibited greater cellular DA in the exponential phase relative to stationary phase when N, not Si or P, was the macronutrient inducing the onset of stationary growth (Auro, 2007).…”

“…Additional events consistent with DA toxicity have been identified. In 2002, 87 sea lions were found stranded on beaches from the border of the USA to Ensenada, on the Baja peninsula, and it was assumed that DA toxicity was the cause of this event (Herná ndez-Becerril et al, 2007 (Rhodes et al, 1998), Monterey Bay, California, USA (Wells et al, 2005) and Chesapeake Bay, Maryland, USA (Thessen et al, 2009) . No adverse biological effects were detected.…”