Selection of effective methods for extracting extracellular polymeric substances (EPSs) from Bacillus megaterium TF10

Bacterial extracellular polymeric substances (EPSs) play an important role in the formation and stabilization of bioaggregates, such as biofilm, microbial flocs and granules. Thus, the selection of appropriate extraction method is of critical importance, which may affect the yield, compositions and properties of EPS. In this work, six different methods used for EPS extraction, including ultrasonication, heating, formaldehyde + NaOH, H ₂SO ₄, glutaraldehyde, and EDTA methods, from Bacillus megaterium TF10, a bacterium with a high EPS-producing capacity isolated from a soil sample, are investigated. These EPS extraction methods are compared in terms of EPS yields and compositions, cell lysis, and flocculation activities and spectrum characteristics of extracted EPS. The results show that both EPS yield and cell lysis generally increase with the extraction time. The heating, formaldehyde + NaOH and H ₂SO ₄ methods lead to a high EPS yield compared to the ultrasonication or EDTA methods, while the ultrasonication and H ₂SO ₄ methods cause much more cell lysis than the formaldehyde + NaOH treatment. The flocculation activities of EPS, which can quantitatively reflect the EPS disruption during extraction, are also evaluated. The flocculation efficiencies of the extracted EPS are found in the order of: formaldehyde + NaOH (30-min formaldehyde treatment and then 60-min NaOH treatment), 92.4% > EDTA (10 h), 92.2% > heating (120 min), 91.6% > glutaraldehyde (15 min), 90.9% > ultrasonication (30 min), 81.0% > H ₂SO ₄ (45 min), 73.2% > control, 59.9%. The IR and EEM spectra suggest that the EPS compositions and structures also vary significantly with the extraction method. Among the six methods, the EDTA method with an extraction time of 10 h was identified to be most effective method to extract EPS from B. megaterium TF10.