Alkaline serine protease AprE plays an essential role in poly-γ-glutamate production during natto fermentation.

Natto is a traditional Japanese food made from soybeans fermented by natto starter strains of Bacillus subtilis natto. It has been suggested that extracellular protease activity released by the bacteria are involved in the production of poly-γ-glutamate (γ-PGA) during natto fermentation. One of the natto starters, strain r22, possesses at least seven genes, each of which encoded an extracellular protease orthologous to its counterpart in B. subtilis 168, aprE, bpr, epr, mpr, nprE, vpr, and wprA, but it was found to lack nprB. Inactivating the aprE ortholog alone resulted in a severe decrease in γ-PGA production and in the total extracellular protease activity. The defect in γ-PGA production of the mutant lacking the aprE ortholog was complemented when the medium was supplemented with sufficient glutamate. These results suggest that the alkaline serine protease encoded by aprE plays an indispensable role in supplying materials to produce γ-PGA. On the other hand, simultaneous inactivation of all the protease genes except for aprE did not significantly affect either γ-PGA production or total protease activity.

Soluble branched (1,4)-beta-D-glucans from Acetobacter species enhance antitumor activities against MHC class I-negative and -positive malignant melanoma through augmented NK activity and cytotoxic T-cell response.

We previously found that an extracellular polysaccharide, AC-1, produced by Acetobacter polysaccharogenes composed of (1,4)-beta-D-glucan with branches of glucosyl residues showed a strong activity to induce production of interleukin (IL)-12 p40 and tumor necrosis factor-alpha by macrophage cell lines in vitro via Toll-like receptor-4 signaling. In the present study, we examined the effects of oral administration of AC-1 on protection against 2 types of murine B16 melanoma lines, major histocompatibility complex (MHC) class I-negative B16L and MHC class I gene-transfected B16K(b) cells. Mice were inoculated subcutaneously with B16L or B16K(b) cells on day 0 and administrated intragastrically with AC-1 or PBS once every 5 days from 1 day before tumor inoculation. The tumor growth was severely retarded in AC-1-treated mice after subcutaneous inoculation with B16L or B16K(b) cells. The AC-1-treated mice showed augmented natural killer (NK) cell activity against B16L cells, and in vivo depletion of NK cells by antiasialoGM1 antibody (Ab) treatment abrogated the antitumor activity in AC-1-treated mice. On the other hand, AC-1-treated mice inoculated with B16K(b) cells developed a significantly higher level of cytotoxic T-lymphocyte response against B16K(b) cells, and in vivo depletion of CD8(+) T cells by anti-CD8 mAb treatment abrogated the antitumor activity. Thus, AC-1 augmented antitumor activity against different tumors via augmentation of different antitumor mechanisms. These results suggest a possible prophylactic application of AC-1 for human neoplasms irrespective of expression levels of their MHC class I molecules.

Immunostimulating properties of intragastrically administered Acetobacter-derived soluble branched (1,4)-beta-D-glucans decrease murine susceptibility to Listeria monocytogenes.

We previously found that AC-1, an extracellular polysaccharide, produced by Acetobacter xylinum and composed of (1,4)-beta-D-glucan with branches of glucosyl residues, showed a strong activity to induce production of interleukin-12 (IL-12) p40 and tumor necrosis factor alpha by macrophages in vitro via Toll-like receptor 4 (TLR-4) signaling. In the present study, we examined the effect of oral administration of AC-1 on protective immunity against Listeria monocytogenes. Mice were given AC-1 or phosphate-buffered saline (PBS) intragastrically 2 days before, on the day of, and 2 days after an intraperitoneal inoculation of L. monocytogenes. The survival rate of AC-1-treated mice was significantly improved and bacterial growth in AC-1-treated mice was severely retarded compared to those of PBS-treated mice after infection with L. monocytogenes. IL-12 p40 levels in serum and magnitudes of CD4+ Th1 and CD8+ Tc1 responses against Listeria antigen were significantly higher in AC-1-treated mice than in PBS-treated mice. The effect of AC-1 on antilisterial activity was diminished in C3H/HeJ mice carrying mutated TLR-4. Thus, AC-1, a potent IL-12 inducer through TLR-4, enhanced protective immunity against L. monocytogenes via augmentation of Th1 responses. These results suggest that infectious processes driven by intracellular microorganisms could be prevented to develop by the (1,4)-beta-D-glucan.

Soluble branched beta-(1,4)glucans from Acetobacter species show strong activities to induce interleukin-12 in vitro and inhibit T-helper 2 cellular response with immunoglobulin E production in vivo.

An extracellular polysaccharide, AC-1, produced by Acetobacter polysaccharogenes is composed of beta-(1,4)glucan with branches of glucosyl residues. We found that AC-1 showed a strong activity to induce production of interleukin-12 P40 and tumor necrosis factor-alpha by macrophage cell lines in vitro. Cellulase treatment completely abolished the activity of AC-1 to induce tumor necrosis factor-alpha production by macrophages, whereas treatment of AC-1 with polymyxin B or proteinase did not affect the activity. Results of experiments using toll-like receptor (TLR) 4-deficient mice and TLR4-transfected human cell line indicated that TLR4 is involved in pattern recognition of AC-1. In vivo administration of AC-1 significantly reduced the serum levels of ovalbumin (OVA)-specific IgE and interleukin-4 production by T cells in response to OVA in mice immunized with OVA. AC-1, a soluble branched beta-(1,4)glucan may be useful in prevention and treatment of allergic disorders With IgE production.