Evaluation of lactobacilli from human sources for uptake and accumulation of selenium.

The trace mineral selenium (Se) is currently in demand for health supplements for human and animal nutrition. In the present study, 25 isolates of Lactobacillus species of human origin from Indian population were screened for their ability to uptake and accumulate Se in a more bioavailable form. Total Se accumulated by cells was measured by inductively coupled plasma emission spectrometry (ICPES) after wet digestion of Se-enriched cultures. Ten out of 25 isolates grew luxuriantly, as red pigmented colonies, on medium amended with different concentrations of sodium selenite. All the strains when grown in a culture medium supplemented with 10 µg/mL sodium selenite (corresponding to 4.5 µg/mL Se) resulted in Se accumulation in the range of 129.5 to 820.0 µg/g of dry weight (d.w.) as measured using the ICPES method. Elemental Se produced due to reduction of sodium selenite by bacteria was seen as irregular globules under the scanning electron microscope (SEM). Out of all the tested cultures, Lactobacillus reuteri NCDC77 was found to have the greatest ability to uptake Se (28.8% of inorganic Se in medium) and total Se accumulated was up to 820 µg/g d.w., significantly higher than that of control (742.5 µg/g d.w.). The findings of present study indicate that lactobacilli from human sources have the ability for uptake and accumulation of Se, and the prolific strain has the potential to be explored as an alternative source of organic dietary Se.

Macrophage activation by bacterial cell walls and related synthetic compounds.

Activation of peritoneal macrophages from guinea pigs by various bacterial cell walls, M-1 endo-N-acetylmuramidase enzymatically digested bacterial cell walls and synthetic muramyl dipeptides was studied in terms of stimulation of [14C] glucosamine incorporation. All test bacterial cell wall preparations significantly increased a [14C]glucosamine uptake by the macrophages. Some of the water-soluble M-1 enzyme digests also exerted stimulating effects on macrophages, although the activity of the digests was found to be weaker than those of original cell walls. Furthermore, an adjuvant-active synthetic MurNAc-L-Ala-D-isoGln (MDP) showed a weak but significant activity, whereas an adjuvant-inactive analog, MurNAc-L-Ala-L-iso-Gln, did not show a significant activity, at least with the dose of 100 microgram. Additional studies with 6-O-acyl derivatives of MDP revealed that 6-O-(2-tetradecylhexadecanoyl)-MDP and 6-O-(3-hydroxy-2-tetradecyl-octadecanoyl)-MDP exhibit stronger macrophage-stimulating effects than MDP. It can be concluded from the above findings that MDP is the essential structure responsible for stimulating the activity of cell walls on guinea pig peritoneal macrophages, but it requires a particle state, which results from an additive character of lipophilicity, to exert the activity fully and effectively.

Ultrastructure and partial characterization of a regular array in the cell wall of Lactobacillus brevis.

The cell wall of Lactobacillus brevis was revealed by electron microscopy to have an outer layer composed of a regular array. The morphological unit of the regular array appeared to consist of four spherical subunits, each about 2 nm in diameter, which were arranged in a tetragonal pattern about 4.5 by 7.0 nm in dimension. The regular array was composed of the tetragonal units in rows in two directions at an angle of about 75 degrees to each other. The average spacing between the rows was about 10 nm in one direction and about 7 nm in the other. The tetragonally arranged subunits were removed from the cell wall by treatment with guanidine hydrochloride, urea, or sodium dodecyl sulfate (SDS) but not by the action of ethylenediaminetetraacetate, nonionic detergents, or proteolytic enzymes except pepsin. The regular subunits were shown to be composed of a protein with a molecular weight of about 51,000 by SDS-polyacrylamide gel electrophoresis.