Fecal microbial DNA extraction, insufficient lysis leads to low yield. Any recommendations?

If the existing kit's lysis is insufficient, enzymatic digestion can be added before bead beating. Add lysozyme (approximately 20 mg/mL, treat at 37°C for 30 minutes) or proteinase K, which significantly breaks down cell walls of Gram-positive bacteria and some thick-walled bacteria; alternatively, heat at 95°C for 10 minutes before bead beating. After enzymatic digestion, follow the original kit procedure by adding lysis buffer and grinding beads, which can improve yield. Note that enzymatic digestion may release more inhibitors, so the subsequent inhibitor removal steps must not be omitted. This method is low-cost and suitable as an emergency fix.

For low yield, first confirm the quantification method. Nanodrop is prone to overestimation due to interference from RNA and impurities. It is recommended to use Qubit dsDNA HS for quantification. A Nanodrop reading of 10-20 ng/μL may be lower on Qubit, but it is not necessarily insufficient for library construction. For 150 mg mouse feces, a total yield of several micrograms is generally within the normal range. The elution volume can be reduced to 50-80 μL, and the elution buffer should be preheated at 65°C. After extraction, run a 0.8% gel to check whether the genome is degraded, and perform small-volume PCR with 16S V3-V4 primers to verify whether the target band can be amplified. This is more meaningful than simply pursuing concentration.

For kits, you can look at dedicated fecal DNA extraction options. Qiagen QIAamp PowerFecal Pro, Tiangen Fecal Genomic DNA Extraction Kit, Magen HiPure Stool DNA Kit, Vazyme, and others all include mechanical lysis beads and inhibitor removal steps, and are compatible with both manual processing and subsequent library preparation for 16S sequencing. Lead times are generally 3-7 days for domestic products and possibly 2-4 weeks for imported ones. It is recommended to first request trial samples, aliquot the same mouse feces, and compare total DNA yield, 260/280, and Ct values from 16S V3-V4 amplification. Do not focus only on yield; residual inhibitors are equally critical.

Grinding condition optimization has the highest priority. 150 mg of feces is too much for many kits; it is recommended to reduce it to 50-100 mg to avoid dilution of the lysis buffer. Use mixed grinding beads (a combination of 0.1 mm silica beads + 0.5 mm glass beads + 2.8 mm steel beads), grind with a tissue homogenizer at 30 Hz for 2-3 minutes, with a 1-minute ice bath in between; if only a vortex mixer is available, shake at 6500-7000 rpm for 10 minutes, but be careful of tube heating. Extending the grinding time beyond 5 minutes can more effectively break the cell walls, but avoid overheating that causes DNA degradation. You can try this first; the cost is almost zero.

When purchasing, focus on whether grinding beads are already included, as many kits require separate purchase, which can easily delay delivery. Clarify whether humic acids, polysaccharides, and other inhibitors are removed, as this greatly affects 16S library preparation. For manual extraction, after adding lysis buffer to the sample, vortex to mix first, then transfer to the bead beating tube to avoid cross-contamination. If the budget is limited, you can purchase mixed grinding beads yourself to use with existing kits, optimize the lysis conditions, and then consider switching brands. Domestic specialized fecal DNA kits usually have much shorter delivery times than imported ones, making them suitable for rapid laboratory replenishment.