Effect of nutrient limitation of cyanobacteria on protease inhibitor production and fitness ofDaphnia magna

Abstract

SUMMARYHerbivore-plant interactions have been well studied in both terrestrial and aquatic ecosystems as they are crucial for the trophic transfer of energy and matter. In nutrient-rich freshwater ecosystems, the interaction between primary producers and herbivores is to a large extent represented by Daphnia and cyanobacteria. The occurrence of cyanobacterial blooms in lakes and ponds has, at least partly, been attributed to cyanotoxins, which negatively affect the major grazer of planktonic cyanobacteria, i.e. Daphnia. Among these cyanotoxins are the widespread protease inhibitors. These inhibitors have been shown (both in vitro and in situ) to inhibit the most important group of digestive proteases in the gut of Daphnia, i.e. trypsins and chymotrypsins, and to reduce Daphnia growth. In this study we grew cultures of the cyanobacterium Microcystis sp. strain BM25 on nutrient-replete, N-depleted or P-depleted medium. We identified three different micropeptins to be the cause for the inhibitory activity of BM25 against chymotrypsins. The micropeptin content depended on nutrient availability: whereas N limitation led to a lower concentration of micropeptins per biomass, P limitation resulted in a higher production of these chymotrypsin inhibitors. The altered micropeptin content of BM25 was accompanied by changed effects on the fitness of Daphnia magna: a higher content of micropeptins led to lower IC 50 values for D. magna gut proteases and vice versa. Following expectations, the lower micropeptin content in the Ndepleted BM25 caused higher somatic growth of D. magna. Therefore, protease inhibitors can be regarded as a nutrientdependent defence against grazers. Interestingly, although the P limitation of the cyanobacterium led to a higher micropeptin content, high growth of D. magna was observed when they were fed with P-depleted BM25. This might be due to reduced digestibility of P-depleted cells with putatively thick mucilaginous sheaths. These findings indicate that both the grazer and the cyanobacterium benefit from P reduction in terms of digestibility and growth inhibition, which is an interesting starting point for further studies.

Copy number variation of a protease gene of Daphnia : Its role in population tolerance

“…BM25 originating from Lake Bysjön, Sweden (Schwarzenberger et al., ) was cultivated in a chemostat on cyanophycean medium at 20°C and constant light (50 μE m −2 sec −1 ). This cyanobacterium does neither contain trypsin inhibitors or microcystins but shows a high chymotrypsin inhibition (Schwarzenberger et al., ). The dilution rate was 0.23 day −1 .…”

“…For this we fed the Daphnia either with a green alga as control food or with 10% of a single‐strand culture of the cyanobacterium Microcystis sp. BM25 that is known to contain chymotrypsin inhibitors (Schwarzenberger, Sadler, & Von Elert, ). This Microcystis strain originates from one of the lakes (Lake Bysjon, Sweden) that was sampled in this study.…”

“…For this we fed the Daphnia either with a green alga as control food or with 10% of a single-strand culture of the cyanobacterium Microcystis sp. BM25 that is known to contain chymotrypsin inhibitors (Schwarzenberger, Sadler, & Von Elert, 2013b).…”

Positive selection of digestive proteases in Daphnia: A mechanism for local adaptation to cyanobacterial protease inhibitors

“…BM25, originating from Lake Bysjön, Sweden (Schwarzenberger, D'Hondt, et al, 2013), was cultivated in a chemostat (dilution rate 0.23/day) on cyanophyceanmedium at 20°C and constant light (50 µE m −2 s −1 ). This cyanobacterium contains neither trypsin inhibitors nor microcystin but shows a high chymotrypsin inhibition (Schwarzenberger, Sadler, & Von Elert, 2013). Carbon concentrations of the autotrophic food suspensions were estimated from photometric light extinction (470 nm) and from carbon extinction equations previously determined and described in detail by Schwarzenberger et al (2017).…”

Is production of protease inhibitors from cyanobacteria nutrient dependent? Comparison of protease inhibitory activities in three species of Oscillatoria isolated from Central India

“…A handful of studies show the role of nutrients, light, temperature (Rohrlack and Utkilen 2007;Halstvedt et al 2008) and bacteria (Sivonen 1990) on production of bioactive compounds from cyanobacteria. Recently, Schwarzenberger et al (2013)showed that the production of protease inhibitor from Microcystis aeruginosa BM 25 is dependent on nitrogen and phosphorus in the culture medium. However, no study compares the production of protease inhibitors from different cyanobacteria under similar culture conditions.…”