Capture of Bacteria from Fermentation Broth by Body Feed Filtration: A Solved Problem?

Abstract

The direct capture of bacteria produced in high cell density fermentation by filtration is not possible once the milliliter-scale has been surpassed. Filtration in the presence of a filter aid (body feed filtration) constitutes a putative and scalable alternative, but only if conditions proposed by industry for large-scale filtration processes, namely, flow rates (for aqueous solutions) in the range of 500-1,500 L/(m(2) x h) and a filter aid concentration of <or=20 g/L, can be met. To this end several filter aids (grades of cellulose, diatomaceous earth, mixes thereof) were tested, albeit with no success. Capture and retention of bacteria was low (not possible in the case of cellulose), and the produced filter cakes were unstable and of low permeability. In the case of the diatomaceous earth close to 100% bacterial capture was possible, but only with filter aid concentrations that were 1 order of magnitude above the proposed limit. By using flocculating agents (Fe(3+)/Al(3+), PEI) either alone or in combination with diatomaceous earth and also the use of positively charged cellulose, bacteria capture could be achieved from several liters of cell suspension (OD(600) <or= 15) in filtration experiments adhering to the industrial recommendations. However, the bacteria were only weakly retained in such cakes and easily released by sudden pressure pulses. Satisfactory results were only obtained by filtration of the bacteria suspension at slightly alkaline pH (8.0, 50 mM Tris buffer) after treatment with sodium-activated bentonite (5 g/L) and PEI (50 mg/L) in the presence of 250 mM NaCl. In such cases 100% of the bacteria could reproducibly be captured in a filtration using 20 g/L of diatomaceous earth as filter aid. The thus produced filter cakes strongly retained the bacteria and showed good filtration performance. The procedure is at present limited to E. coli culture with biomass contents of OD(600) <or= 15. Cultures with higher OD(600) have to be diluted prior to filtration.

Integrated xylitol production by fermentation of hardwood wastes

“…However, polymer pretreatment on the membrane surface may be required before filtration to enhance performance by providing additional steric barriers and ensuring the retention of millimetrescale cell debris and proteins. 26,27 Eucalyptus is the predominant planted hardwood species worldwide. 28 As a result of improved genetics and silviculture, 29 it supplies increasing quantities of raw materials for wood pulping.…”

Integration of Bacteria Capture via Filtration and in Situ Lysis for Recovery of Plasmid DNA under Industry-Compatible Conditions

“…2000 L/(m 2 h)), presumably due to the reduced viscosity of the aqueous solution at 70 °C. In addition it is likely that the alumina‐based hydrogel released by the bentonite during incubation (19) is partially dissolved at the acidic pH and comparatively high NaCl concentration in case of the CNS lysis buffer. This will also reduce the backpressure of the filter cake.…”

“…Bacteria Capture by Filtration. For capture of the bacteria via filtration, the previously published protocol was used (19). Briefly, the bioreactor cultures were stopped before reaching the maximal biomass values, typically at an OD 600 of ca.…”

“…The latter constrain posed a particular problem, as such low filter aid concentrations no longer allowed the deposition of a stable filter cake of diatomaceous earth into which the bacteria are merely inserted. We have recently proposed a filtration protocol that makes use of bentonite and polycations such as PEI (polyethyleneimine) for the active retention of the bacteria in the filter cake while diatomaceous earth serves once more as principal filter aid, which complies to the industrial requirements (19). In the present contribution, we intend to show that the integration of bacteria capture with in situ lysis is equally possible in the case of such much more complex filter cakes.…”

Deciphering the aggregation mechanism of bacteria (Shewanella oneidensis MR1) in the presence of polyethyleneimine: Effects of the exopolymeric superstructure and polymer molecular weight

“…In that case, the optimal flocculation concentration, addressed either by measurement of a filtration time [22] or that of an aggregate size [23], generally decreases with increasing polymer molecular weight in the 10000 to 100000g/mol range [2]. The aggregation of bacteria mediated by low PEI molecular weights (<2000 g/mol) has been shown to lead to longer filtration times, and the restabilization of bacterial suspensions at high polymer concentrations has not been observed [2,22,24]. It has also been reported that the binding of PEI with LPS leads to the release of associated material from the bacterial cell [25,26], inducing bacterial membrane permeabilization [27].…”