Monod parameterization and competition at low iron among freshwater cyanobacteria and chlorophytes

Low cobalt limits cyanobacteria heterocyst frequency in culture but potential for cobalt limitation of frequency in nitrogen-limited surface waters is unclear

“…Facey et al (2022) found that growth of the non-heterocystous, non-N fixing cyanobacterium Microcystis aeruginosa was most severely inhibited in cultures when dissolved Co was less than 0.34 nmol L -1 so the threshold for Microcystis must have been less than 0.34 nmol L -1 . Monod growth thresholds for Fe reported by Shah et al (2023) for three cyanobacteria (two of which were used in this study) under N-replete and N-deplete conditions and two eukaryotic algae ranged from 0.02 to 1.20 nmol L -1 , with three of the seven thresholds below 0.17 nmol L -1 . Cyanobacteria thresholds for other metabolically essential trace metals are probably in the sub-nanomomolar range as well.…”

“…Alternatively, Co buildup could be due to loss from senescing cells or excretion by viable cells (Bonnet et al, 2012). Whatever the nature of the concentration mechanism, it follows from Michaelis-Menten transport and Monod growth kinetics (Shah et al, 2023) that a buildup of Co next to cellular membranes could increase Co transport and growth rates although dissociation of Co strongly bound to ligands with high binding affinities would likely have to be biologically facilitated first (Quigg et al, 2006;Worms et al, 2006;Fujii et al, 2010;Rose, 2012).…”