Abilities And Properties Of Lactobacilli Strains To Bind Benzo(a)pyrene

Lactic acid bacteria have been reported to have antimutagenic/anticarcinogenic properties in vitro and in vivo. One possible mechanism for this effect involved a physical binding of the mutagenic compounds to the bacteria. The objectives of this present study were: (1) to evulate the binding of benzo(a)pyrene (B(a)P) from contaminated solution by 53 lactic acid bacteria strains; (2) to use 2 selected strains, i.e., Lactobacillus plantarum 121 and Lactobacillus pentosus ML32 to deal with their B(a)P-binding; and (3) to investigate possible mechanisms of 2 lactobacilli strains to bind B(a)P in the stimulation of gastro-intestinal environments. All bacterial cells and B(a)P were incubated at 37°C for 4 h in combination, and the amount of unbound B(a)P, quantitated by HPLC, was used to show the ability of each strain to binding B(a)P in this study. The following are main results.1. The percentage of B(a)P-binding was 65.9% for 121 and 64.9% for ML32. Physical factors affecting two lactobacilli strains to bind B(a)P included incubation time, temperature and bacterial cell viability. The maximum binding of the strains 121 and ML32 to B(a)P took place at pH 4 and 5, respectively. Their B(a)P-binding increased to the maximum as the concentrations of Ca2+ and Mg2+ in media were higher than 0.05 mol/mL. Use of TCA, SDS, Triton-X100 and enzymes including lysozyme, alkaline protease, neutral proteinase and pronase E to treat cells affected the performances of the two strains to bind B(a)P, producing an irreversible B(a)P-binding.The stimulation of gastrointestinal environments showed that the percentage of B(a)P-binding by the two lactobacilli strains depended largely upon pH and bile salt concentrations, but less upon treating time. Trypsin had only influence on the ability of the strain 121 to bind B(a)P, but not the strain ML32. The presence of benzene in washing cell impaired the ability of the two strains to bind B(a)P.2. A concentration of B(a)P ranging from 10 or 50μg/mL in media had no influence on the growth and survival of the two strains. The two lactobacilli strains removed 79% of B(a)P from environments after grown in B(a)P-containing media at 37°C for 24 h. Meawhile, no clear activity loss for the strains 121 and ML32 was observed after they bound to B(a)P.3. The cell wall might be responsible for the B(a)P-binding. The binding of B(a)P to the cell wall in Gram-positive bacteria was much higher than in Gram-negative bacteria. The percentage of B(a)P-binding reached 80.6% for the strain 121 and 78.3% for the strain ML32 if their cell wall was not damaged. The B(a)P-binding ability of the two lactobacilli strains decreased quickly in the absence of cell wall. The percentage of their B(a)P-binding was even less than 20%. The cell-free extracts of the two lactobacilli strains were observed to have a very low B(a)P-binding, only about 3.4% for the strain 121 and 2.1% for the strain ML32. Moreover, peptidoglycan liberated from the cell wall was recognized as the main binding receptor for B(a)P, and its integrity was very important in binding. The binding percentage of peptidoglycans of the two strains to B(a)P was 93% and 96.7%, respectively. Data from lysozyme, UV-visible absorption, chemical analysis of protein, total sugar and neutralsugars proved that the peptidoglycans purfied were from the cell walls of the two lactobacilli strains.4. In conclusions, lactobacilli strains tested in this present study were very potential as probiotics for the remove of B(a)P from their environments due to cell surface-binding. Their B(a)P-binding that seems to be a physical phenomenon might depend on the surface structure of the bacterial cells.