Predominant effect of host genetics on levels of Lactobacillus johnsonii bacteria in the mouse gut

Abstract

The gut microbiota is strongly associated with the well-being of the host. Its composition is affected by environmental factors, such as food and maternal inoculation, while the relative impact of the host's genetics have been recently uncovered. Here, we studied the effect of the host genetic background on the composition of intestinal bacteria in a murine model, focusing on lactic acid bacteria (LAB) as an important group that includes many probiotic strains. Based on 16S rRNA gene genotyping, variation was observed in fecal LAB populations of BALB/c and C57BL/6J mouse lines. Lactobacillus johnsonii, a potentially probiotic bacterium, appeared at significantly higher levels in C57BL/6J versus BALB/c mouse feces. In the BALB/c gut, the L. johnsonii level decreased rapidly after oral administration, suggesting that some selective force does not allow its persistence at higher levels. The genetic inheritance of L. johnsonii levels was further tested in reciprocal crosses between the two mouse lines. The resultant F1 offspring presented similar L. johnsonii levels, confirming that mouse genetics plays a major role in determining these levels compared to the smaller maternal effect. Our findings suggest that mouse genetics has a major effect on the composition of the LAB population in general and on the persistence of L. johnsonii in the gut in particular. Concentrating on a narrow spectrum of culturable LAB enables the isolation and characterization of such potentially probiotic bacterial strains, which might be specifically oriented to the genetic background of the host as part of a personalized-medicine approach.

Fig. 1.

TRFLP patterns of fecal LAB populations obtained from C57BL/6J and BALB/c mice. LAB were grown on m-Enterococcus agar under anaerobic conditions. DNA fragments were observed using fluorescent 6-carboxyfluorescein (FAM)-labeled primer for 16S PCR amplification, followed by digestion with MspI restriction enzyme and fragment size analysis using an ABI 3130 genetic analyzer. The sizes of specific fragments are given.

Fig. 2.

Levels of L. johnsonii in fecal samples of mouse lines C57BL/6J (black bars) and BALB/c (white bars). Males (♂) and females (♀) were tested separately (five mice per group). The levels are expressed as proportions of L. johnsonii colonies out of the total number of colonies grown on m-Enterococcus agar plates and are given as average values of three and five independent biological replicates for males and females, respectively. L. johnsonii was enumerated using colony hybridization with an L. johnsonii-specific probe. Bars labeled with different letters are significantly different at an α value of <0.05 by two-way ANOVA followed by a Tukey HSD test. The error bars indicate standard errors.

Fig. 3.

Fecal levels of L. johnsonii after feeding C57BL/6J and BALB/c mice with L. johnsonii isolated from C57BL/6J mice. Both experimental (exp.) and control (ctrl.) groups (five mice per group) received antibiotic treatment for 3 days prior to the feeding. Experimental groups were fed L. johnsonii on days 0, 1, and 2 of the trial (indicated by arrows). L. johnsonii levels are expressed as proportions of L. johnsonii colonies out of the total number of colonies grown on m-Enterococcus agar plates. Levels are given as average values of two technical replicates. L. johnsonii was enumerated using colony hybridization with an L. johnsonii-specific probe.

Fig. 4.

L. johnsonii levels in fecal samples from F1 offspring (gray bars) and the parental mouse lines C57BL/6J (black bars) and BALB/c (white bars), with five mice per group. F1 offspring resulted from two separate reciprocal crosses: ♀BALB/c × ♂C57BL and ♂BALB/c × ♀C57BL. Levels are expressed as proportions of L. johnsonii colonies out of the total number of colonies grown on m-Enterococcus agar plates and are given as average values of four independent biological replicates. L. johnsonii was enumerated using colony hybridization with an L. johnsonii-specific probe. Bars labeled with different letters are significantly different at an α value of <0.05 by ANOVA, followed by a Tukey HSD test. The error bars indicate standard errors.