 Bacterial growth rates - For each metagenome sample, the investigators will compute a vector that corresponds to the growth rate of each bacteria in the sample, using a novel method that was recently developed for this purpose. Briefly, by examining the pattern of sequencing read coverage depth across the length of different bacterial genomes, the investigators found that many bacteria exhibit a prototypical coverage pattern, consisting of a single trough and a single peak. Notably, the location of the peak coincides with the bacterias known origin of replication, suggesting that the added read coverage near the peak represents newly replicated DNA. For any given bacteria, the ratio between the peak and trough coverage varies greatly across samples from different human gut microbiomes, with high ratios being similar to those obtained during exponential growth phase of bacteria grown in culture, and low ratios being similar to growth in stationary phase. 