Cellular characteristics and growth behavior of iron‐limited Microcystis aeruginosa in nutrient‐depleted and nutrient‐replete chemostat systems

Abstract

Cellular responses of Fe‐limited Microcystis aeruginosa were investigated under nutrient‐depleted and ‐replete conditions. Cellular growth, Fe quota and Fe uptake kinetics were examined in chemostat systems using nutrient‐replete Fraquil* (where all nutrients except for Fe are present at sufficient level to achieve optimal growth) and nutrient‐deplete Fraquil* (where some nutrients in addition to Fe are potentially growth‐limiting factors). For both nutrient conditions, cellular Fe quota increased with increasing dilution rate in a manner consistent with Droop theory. However, the Fe quota in nutrient‐deplete Fraquil* was determined to be lower, indicating lower cellular Fe requirement in the nutrient‐depleted condition. Short‐term Fe uptake assays indicated that cells acclimated in nutrient‐replete conditions adjust to various degrees of Fe stress by solely increasing maximum Fe uptake rate, consistent with expected negative feedback regulation. In contrast, the maximum Fe uptake rate decreased with increasing degree of Fe limitation in the nutrient‐depleted chemostat (particularly nitrate and molybdenum in this study). This non‐negative feedback regulation is likely associated with lower Fe requirement for specific functions (e.g., intracellular nitrate reduction). Cellular affinity for Fe uptake and cellular size were independent of degree of Fe stress for both nutrient conditions.

Micronutrients as growth limiting factors in cyanobacterial blooms; a survey of freshwaters in South East Australia

“…This study joins a growing list that have observed an important role of micronutrients in structuring phytoplankton communities and increasing cyanobacterial growth in physically and chemically diverse freshwater systems. For example, Downs et al (2008) noted a stimulation of the cyanobacterium Anabaena flos-aquae upon addition of cobalt, copper, manganese and a trace metal mixture, while a number of studies have observed iron limitation of cyanobacteria growth (Wever et al 2008;Molot et al 2010;Harland et al 2013;Fujii et al 2016).…”

Physiological responses of the freshwater N2‐fixing cyanobacterium Raphidiopsis raciborskii to Fe and N availabilities

“…Dissolved unchelated Fe(II) (Fe(II)') arising from the photoreductive dissociation of Fe(III)-EDTA has been shown to be the major Fe substrate in EDTA-buffered culture medium at pH 8 (Fujii et al, 2011b;Dang et al, 2012;Fujii et al, 2016). Here, the steady-state concentration of Fe(II)' was calculated using the same kinetic model and assuming that Fe(II)' is the major form of Fe available for uptake by R. raciborskii (SI4 and Table S2 in the Supporting Information respectively).…”

A Review of the Effect of Trace Metals on Freshwater Cyanobacterial Growth and Toxin Production

“…A growing body of literature demonstrates the impact of trace metals (alone or in combination with macronutrients) on phytoplankton growth [34,69,70,71,72]. For example, Downs et al [35] observed that the addition of Cu, Mo or Co during a cyanobacterial bloom in a eutrophic lake stimulated primary productivity by up to 40%, indicating a large contribution of micronutrients to eutrophication.…”

“…Culture-based experiments form most of the literature on cyanobacteria–metal interactions (≈63% of the studies from Table 1). While culture experiments often demonstrate unambiguous relationships between a single species growth and a given micronutrient, as demonstrated by Fujii et al [70], it is also important to examine these relationships under field conditions which take into account environmentally relevant concentrations of trace metals, particularly as selective pressures and behaviours of culture-raised organisms can differ from those in natural systems [94]. Nutrient amendment bioassays are a useful tool in bridging the gap between culture and field studies, and have been used effectively in studies such as de Wever et al [64] and Zhang et al [37].…”