Nested Constraint Fields in Biological Growth: Evidence from Coherence Transitions in Microbial Growth Dynamics (Paper 2, V2)

This work presents an empirical analysis of isolated microbial growth dynamics using a dimensionless, null-first framework designed to expose internal organization rather than absolute kinetics. By rescaling time using each trajectory’s early exponential doubling time, we remove trivial rate and scale effects and analyze growth in a common internal reference frame. Across isolated bacterial growth trajectories, we identify conditional internal regimes that cannot be reproduced by smooth logistic or Gompertz growth. These regimes vanish under aggregation in microbial communities and are absent in null models, demonstrating that they are intrinsic to isolated growth dynamics rather than experimental or statistical artifacts. To characterize how growth reorganizes upon entering such regimes, we introduce an internal coherence measure based on coupling between early, mid, and late growth phases. We observe a robust, non-monotonic coherence transition: internal coupling rises sharply at intermediate growth depth and collapses at greater depth, even as internal variability continues to increase. Chemical perturbations shift the depth at which this transition occurs but do not eliminate the structure. The results support an interpretation in which biological growth proceeds within nested constraint fields that regulate how complexity is integrated. Progression into larger fields is marked by increased internal coherence, while failure to evolve sufficient organization leads to an effective evolutionary ceiling. Growth is therefore limited not by replication alone, but by the capacity to coordinate what has already been built. This study forms the micro-scale counterpart to Nested Coherence Across Scales: Multi-domain Evidence and a Minimal Triad Invariant (Halldórsson & Antonson, 2025), together suggesting a common organizational structure spanning biological and geophysical systems.