Summary Cyanobacterial blooms are a worldwide phenomenon in both marine and freshwater ecosystems and are predicted to occur more frequently due to global climate change. However, our future water resources may also simultaneously suffer from other environmental threats such as elevated amounts of humic content and consequent increased water colour, a phenomenon called ‘brownification’. In order to investigate the effects of temperature and water colour in combination, we performed a mesocosm experiment combining a 3 °C increase in temperature and a doubling in water colour. With this, we created a projected future scenario for our water resources, and we specifically focused on how these changes would affect cyanobacterial bloom formation and toxicity. We showed that despite total cyanobacterial biomass remaining unaffected, the abundance of one individual cyanobacterial species, Microcystis botrys, increased in response to the combination of elevated temperature and increased water colour. Furthermore, population fluctuations in M. botrys explained the majority of the variations in microcystin concentrations, suggesting that this species was responsible for the more than 300% higher microcystin concentrations in the future scenario treatment compared to the ambient scenario. Hence, it was not a change in cyanobacterial biomass, but rather a species‐specific response that had the most profound impact on bloom toxicity. We argue that understanding such species‐specific responses to multiple stressors is crucial for proper management decisions because toxic blooms can significantly affect both biodiversity and ecosystem functioning, as well as ecosystem services such as drinking water supply and recreation.

High poly(3-hydroxybutyrate) (PHB) content and volumetric productivity were achieved by fed-batch culture of Halomonas boliviensis using a defined medium. Initial shake flask cultivations in a minimal medium revealed that the growth of H. boliviensis was supported only when the medium was supplemented with aspartic acid, glycine, or glutamine. Addition of 0.1% (w/v) glutamine in the medium resulted in the highest cell dry weight (CDW; 3.9 g l(-1)). Glutamine was replaced by the less expensive monosodium glutamate (MSG) in the medium without any notable change in the final cell density. Effect of initial concentrations of NH(4)Cl and K(2)HPO(4) on cell growth and PHB accumulation by H. boliviensis was then analyzed using a fed-batch fermentation system. The best conditions for PHB production by H. boliviensis were attained using 0.4% (w/v) NH(4)Cl and 0.22% (w/v) K(2)HPO(4) and adding MSG intermittently to the fermentor. Poly(3-hydroxybutyrate) content and CDW reached 90 wt.% and 23 g l(-1), respectively, after 18 h of cultivation. In order to increase CDW and PHB content, MSG, NH(4)Cl, and K(2)HPO(4) were initially fed to the fermentor to maintain their concentrations at 2%, 0.4%, and 0.22% (w/v), respectively, and subsequently their feed was suppressed. This resulted in a CDW of 44 g l(-1), PHB content of 81 wt.%, and PHB volumetric productivity of 1.1 g l(-1) h(-1).

The paper reports a study involving the use of Halomonas boliviensis, a moderate halophile, for co-production of compatible solute ectoine and biopolyester poly(3-hydroxybutyrate) (PHB) in a process comprising two fed-batch cultures. Initial investigations on the growth of the organism in a medium with varying NaCl concentrations showed the highest level of intracellular accumulation of ectoine (0.74 g L(-1)) at 10-15% (w/v) NaCl, while at 15% (w/v) NaCl, the presence of hydroxyectoine (50 mg L(-1)) was also noted. On the other hand, the maximum cell dry weight and PHB concentration of 10 and 5.8 g L(-1), respectively, were obtained at 5-7.5% (w/v) NaCl. A process comprising two fed-batch cultivations was developed-the first culture aimed at obtaining high cell mass and the second for achieving high yields of ectoine and PHB. In the first fed-batch culture, H. boliviensis was grown in a medium with 4.5% (w/v) NaCl and sufficient levels of monosodium glutamate, NH (4) (+) , and PO (4) (3-) . In the second fed-batch culture, the NaCl concentration was increased to 7.5% (w/v) to trigger ectoine synthesis, while nitrogen and phosphorus sources were fed only during the first 3 h and then stopped to favor PHB accumulation. The process resulted in PHB yield of 68.5 wt.% of cell dry weight and volumetric productivity of about 1 g L(-1) h(-1) and ectoine concentration, content, and volumetric productivity of 4.3 g L(-1), 7.2 wt.%, and 2.8 g L(-1) day(-1), respectively. At salt concentration of 12.5% (w/v) during the second cultivation, the ectoine content was increased to 17 wt.% and productivity to 3.4 g L(-1) day(-1).

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