Xylan-mediated aggregation of Lactobacillus brevis and its relationship with the surface properties and mucin-mediated aggregation of the bacteria

Abstract

Some Lactobacillus brevis strains were found to aggregate upon the addition of xylan after screening for lactic acid bacteria that interact with plant materials. The S-layer proteins of cell surface varied among the strains. The strains that displayed xylan-mediated aggregation retained its ability even after the removal of S-layer proteins. L. brevis had negative zeta potentials. A correlation between the strength of aggregation and zeta potential was not observed. However, partial removal of S-layer proteins resulted in decreases in the electric potential and aggregation ability of some strains. Therefore, xylan-mediated aggregation of L. brevis was considered to be caused by an electrostatic effect between the cells and xylan. L. brevis also aggregated in the presence of mucin, and the strengths of aggregation among the strains were similar to that induced by xylan. Thus, xylan- and mucin-mediated L. brevis aggregation was supposed to be caused by a similar mechanism.

Direct Imaging of Carboxymethyl Cellulose-mediated Aggregation of Lactic Acid Bacteria Using Dark-field Microscopy

“…16,17 Xylan-mediated aggregation of LAB was considered to be caused by xylan affinity to cells, since partial removal of the S-layer proteins on LAB cells by LiCl extraction significantly reduced xylan-mediated aggregations in previous study. 13 Similar mechanisms would be expected to occur between LAB and CMC.…”

“…Cell cultivation and preparation of cell suspension were performed as described previously. 13 Briefly, the cells were cultured in Lactobacilli MRS broth (Becton, Dickinson and Company, Franklin Lakes, NJ) at 30 C for 24 h and harvested by centrifugation. After washing the cells with saline (0.9% sodium chloride), cell suspension in saline (OD600nm = 1.0) was prepared and used for microscopic observations of cell aggregation.…”

“…11,12 Recently, Saito et al reported aggregations of LAB mediated by xylan. 13 Xylan is a negatively charged polysaccharide made from units of xylose. Xylan is almost as ubiquitous as cellulose in plant-cell walls, and contains predominantly β-D-xylose units linked as in cellulose.…”

“…The xylan-mediated aggregation of LAB was considered to be caused by xylan affinity to cells. 13 This model can be helpful to understand the mechanisms of biofilm formations, and to develop probiotic products.…”

“…13 However, aggregation results from an interaction process among LAB cells, shapes and sizes of aggregates in LAB suspension have never been directly visualized and measured. Therefore, we tried direct observations of aggregation process of LAB in real time using DFM.…”