Variation in resource competition traits among strains is affected by their microbiomes.

Freshwater harmful algal blooms are often dominated by , a phylogenetically cohesive group of cyanobacteria marked by extensive genetic and physiological diversity. We have previously shown that this genetic diversity and the presence of a microbiome of heterotrophic bacteria influences competitive interactions with eukaryotic phytoplankton. In this study, we sought to explain these observations by characterizing Monod equation parameters for resource usage (maximum growth rate , half-saturation value for growth and quota) as a function of N and P levels for four strains (NIES-843, PCC 9701, PCC 7806 [WT], and PCC 7806 Δ) in presence and absence of a microbiome derived from isolated from Lake Erie. Results indicated limited differences in maximum growth rates but more pronounced differences in half-saturation values among strains. The largest impact of the microbiome was reducing the minimal nitrogen concentration sustaining growth and reducing half saturation values, with variable results depending on the strain. strains also differed from each other in their N and P quotas and the extent to which microbiome presence affected them. Our data highlight the importance of the microbiome in altering -intrinsic traits, strain competitive hierarchies, and thus bloom dynamics. As quota, , and are commonly used in models for harmful algal blooms, our data suggest that model improvement may be possible by incorporating genotype dependencies of resource-use parameters.