Figure 2.

Effects of filter material, pore size, and sampled biomass. (a) Filtration times (s) for five OD₆₀₀ units of E. coli rinsed with 10 mL warm (37 °C) water under a controlled vacuum on polyvinylidene difluoride (PVDF), hydrophilic polytetrafluoroethylene (PTFE), and nylon filters with a pore size of 0.22 µm, 0.45 µm, or 0.65 µm. The average ± SD of n = 3–4 technical replicates is presented. (b) The proportions of E. coli from three common laboratory setups belonging to different diameter-ranges (µm), as estimated by light microscopy. Presented for rich medium in shake flask, mineral medium in shake flask, and mineral medium in bioreactor. The largest filter pore size included in this study is indicated by a dashed line. The average of 1–3 biological replicates, each with n ≥ 5 technical replicates is presented. More than 350 cells were measured per biological replicate. (c) Colony forming units (CFU)/mL in five OD₆₀₀ units of an unfiltered E. coli culture, and in the corresponding E. coli filtrate from PVDF filters with a pore size of 0.22 µm, 0.45 µm, and 0.65 µm. The average ± SD of n = 3 technical sampling replicates each plated in 1–3 parallels is presented. (d) The filtration time (s) and (e) adenylate energy charge (AEC) measured for five and ten OD₆₀₀ units of E. coli rinsed with 10 mL warm (37 °C) water under a controlled vacuum on PVDF filters with a pore size of 0.45 µm. The average of n = 4–8 replicate samplings is presented. Significance levels from two-tailed t-tests assuming equal variances are marked in (d,e) *: p ≤ 0.05; ****: p ≤ 0.0001. #; number.