Aflatoxin B1 and Sterigmatocystin Binding Potential of Lactobacilli

Abstract

Due to global climate change, mould strains causing problems with their mycotoxin production in the tropical-subtropical climate zone have also appeared in countries belonging to the temperate zone. Biodetoxification of crops and raw materials for food and feed industries including the aflatoxin B1 (AFB1) binding abilities of lactobacilli is of growing interest. Despite the massive quantities of papers dealing with AFB1-binding of lactobacilli, there are no data for microbial binding of the structurally similar mycotoxin sterigmatocystin (ST). In addition, previous works focused on the detection of AFB1 in extracts, while in this case, analytical determination was necessary for the microbial biomass as well. To test binding capacities, a rapid instrumental analytical method using high-performance liquid chromatography was developed and applied for measurement of AFB1 and ST in the biomass of the cultured bacteria and its supernatant, containing the mycotoxin fraction bound by the bacteria and the fraction that remained unbound, respectively. For our AFB1 and ST adsorption studies, 80 strains of the genus Lactobacillus were selected. Broths containing 0.2 µg/mL AFB1and ST were inoculated with the Lactobacillus test strains. Before screening the strains for binding capacities, optimisation of the experiment parameters was carried out. Mycotoxin binding was detectable from a germ count of 10⁷ cells/mL. By studying the incubation time of the cells with the mycotoxins needed for mycotoxin-binding, co-incubation for 10 min was found sufficient. The presence of mycotoxins did not affect the growth of bacterial strains. Three strains of L. plantarum had the best AFB1 adsorption capacities, binding nearly 10% of the mycotoxin present, and in the case of ST, the degree of binding was over 20%.

Keywords: aflatoxin B1; detoxification; lactobacilli; mycotoxin binding; sterigmatocystin.

Figure 1

The effect of bacterial concentration on the aflatoxin B1 (continuous line) and sterigmatocystin (dashed line) binding of L. pentosus TV3 (black), L. paracasei MA2 (red), and L. plantarum TS23 (green). (logN means the logarithm of the number of colony-forming units per mL of bacterial cell suspension).

Figure 2

The effect of incubation time of 10 min (blue) and 48 h (white) on the aflatoxin B1 binding of L. pentosus TV3, L. paracasei MA2, L. plantarum TS23, L. graminis TV24, and L. salivarius SK63. (means ± standard deviation, N = 5).

Figure 3

The effect of aflatoxin B1 (A) and sterigmatocystin (B) at concentration 0.2 µg/mL on the cell count L. pentosus TV3, L. paracasei MA2, L. plantarum TS23 (control-white, with mycotoxin-blue). (means±standard deviation, N = 3) (logN means the logarithm of the number of colonies forming units per ml of bacterial cell suspension).

Figure 4

Lactobacillus strains with AFB1 binding capacities above 5% at 0.2 µg/mL mycotoxin concentration in MRS broth.

Figure 5

Lactobacillus strains with AFB1 binding capacities of 3–5% at 0.2 µg/mL mycotoxin concentration in MRS broth.

Figure 6

Phylogenetic relationship of the best aflatoxin B1 binding Lactobacillus strains.

Figure 7

Sterigmatocystin binding capacities (%) of Lactobacillus strains at 0.2 µg/mL mycotoxin concentration in MRS broth.

Figure 8

Phylogenetic relationship of the best sterigmatocystin binding Lactobacillus strains.