pH-gradient ion-exchange microbial cell chromatography as a simple method for microbial separation

Separation of Microalgae by a Dynamic Bed of Magnetite-Containing Gel in the Application of a Magnetic Field

Microalgae are now known as potential microorganisms in the production of chemicals, fuel, and food. Since microalgae live in the sea and the river, they need to be harvested and separated and cultured for further usage. In this study, to separate microalgae, a bed of magnetite-containing gel (Mag gel, 190 µm) was packed in the column by the application of a magnetic field for the separative elution of injected microalgae (including mainly four species), cultured at Saga University in Japan. The applied magnetic field was set at a constant and dynamic-convex manner. At a constant magnetic field of 0.4–1.1 T, the elution percentage of the microalgae at less than 5 µm was 30–50%. At 1.1 T, the larger-sized microalgae were eluted at a percentage of 20%, resulting in the structural change of the bed by the applied magnetic field. In a convex-like change of the magnetic field at 1.1 T ⇄ 0.4 T, the smaller-sized microalgae were selectively eluted, whereas at 1.1 T ⇄ 0.8 T, the larger-sized microalgae were eluted. Dynamic convex-like changes by the magnetic field selectively eluted the microalgae, leading to the separation and the extraction of potential microalgae.

Separation of microalgae using a compacted magnetite-containing gel bed

Separation of microalgae of various sizes and shapes is an important process that enables subsequent production of useful compounds. Herein, the separation of microalgae was accomplished using a magnetite-containing gel (42 μm) packed into a column. An algal suspension was injected into the top of the gel bed, after which water was passed through the column. The pressure generated during the process caused the lower domain of the gel bed to deform, resulting in narrowed gaps between the gel beads. When a suspension of Nannochloropsis sp. (0.0069-0.69 g L^-1) was loaded and water was passed through the column at an applied pressure of 0.01-0.10 MPa, the majority of microalgae were captured within the upper domain of the gel bed, while only 20% were captured within the lower domain. The amount of Nannochloropsis sp. captured was expressed by an ordinary differential equation to determine the capture coefficient, K, and the maximum capture amount, Q_max. As pressure increased, gel gaps narrowed, K increased, and Q_max decreased because of a reduction in the number of effective capture sites upon compaction of the gel. When a mixed suspension of Anabaena sp., Monoraphidium sp., and Desmodesmus sp. (0.069 g L^-1 each) was injected into the gel bed at an applied pressure of 0.01 MPa, only Anabaena sp. was captured at the bottom of the gel bed. This device can be applied for the separation of microalgae in rivers and the sea.

Temperature-gradient incubation isolates multiple competitive species from a single environmental sample

High-throughput sequencing has allowed culture-independent investigation into a wide variety of microbiomes, but sequencing studies still require axenic culture experiments to determine ecological roles, confirm functional predictions and identify useful compounds and pathways. We have developed a new method for culturing and isolating multiple microbial species with overlapping ecological niches from a single environmental sample, using temperature-gradient incubation. This method was more effective than standard serial dilution-to-extinction at isolating methanotrophic bacteria. It also highlighted discrepancies between culture-dependent and -independent techniques; 16S rRNA gene amplicon sequencing of the same sample did not accurately reflect cultivatable strains using this method. We propose that temperature-gradient incubation could be used to separate out and study previously ‘unculturable’ strains, which co-exist in both natural and artificial environments.

Size Separation of Silica Particles using a Magnetite-Containing Gel-Packed Column

A magnetite-containing gel was prepared by water-in-oil radical polymerization of N,N-dimethylacrylamide and N,N’-methylenebisacrylamide in the presence of magnetite. The size of the prepared gel particles was 86 µm. The obtained magnetite-containing gel was packed in a column and first permeated with water, which revealed that the gel displayed a nonlinear response to pressure drop with increasing flow rate. Thus, the gel particles at the bottom of the column felt more pressure from the fluid than those at the top, causing greater deformation of the gel particles at the bottom of the column than at the top. The gaps between the packed gel particles functioned as pores to filter particles of appropriate size and morphology. An industrial silica particle suspension with particle sizes of 300 nm, 800 nm, and 10 µm was permeated through the gel layer. The smallest (300 nm) silica particles passed through the column. The filtered silica particles were recovered from the gel layer by using a magnet to separate the magnetite-containing gel from the filtered silica particles. This magnetite-containing gel has wide application prospects for the separation of not only ceramics but also other colloids.