2-Fucosyllactose Metabolism by Bifidobacteria Promotes Lactobacilli Growth in Co-Culture

Abstract

Breastfeeding is recognized as the gold standard in infant nutrition, not only because of breastmilk's intrinsic nutritional benefits but also due to the high content of different bioactive components such as 2-fucosyllactose (2'FL) in the mother's milk. It promotes the growth of its two major consumers, Bifidobacterium longum ssp. infantis and Bifidobacterium bifidum, but the effect on other intestinal microorganisms of infant microbiota remains incompletely understood. pH-uncontrolled fecal cultures from infants donors identified as "fast 2'FL -degrader" microbiota phenotype were used for the isolation of 2'FL-associated microorganisms. The use of specific selective agents allowed the successful isolation of B. bifidum IPLA20048 and of Lactobacillus gasseri IPLA20136. The characterization of 2'FL consumption and its moieties has revealed more pronounced growth, pH drop, and lactic acid production after 2'FL consumption when both microorganisms were grown together. The results point to an association between B. bifidum IPLA20048 and L. gasseri IPLA20136 in which L. gasseri is able to use the galactose from the lactose moiety after the hydrolysis of 2'FL by B. bifidum. The additional screening of two groups of bifidobacteria (n = 38), fast and slow degraders of 2'FL, in co-culture with lactobacilli confirmed a potential cross-feeding mechanism based on degradation products released from bifidobacterial 2'FL break-down. Our work suggests that this phenomenon may be widespread among lactobacilli and bifidobacteria in the infant gut. More investigation is needed to decipher how the ability to degrade 2'FL and other human milk oligosaccharides could influence the microbiota establishment in neonates and the evolution of the microbiota in adult life.

Keywords: 2′FL; bifidobacteria; cross-feeding; degradation status; lactobacilli.

Figure 1

Schematic representation of strategies conducted to obtain isolates in pure cultures of B. bifidum IPLA20048 and L. gasseri IPLA20136 from a single colony obtained in MRS supplemented with 2′FL by spread plating the feces from infants with a 2′FL degrader phenotype. “LP” supplement containing lithium chloride 0.2% w/v and sodium propionate 0.3%, “TOS” Transgalactooligosaccharide-propionate agar.

Figure 2

(A) Consumption of 2′FL and its constituents (Δmg/100 mL) and (B) variation in acetic (brown bars) and lactic acid (yellow bars) levels (Δmg/100 mL) after 24 h of incubation of B. bifidum IPLA20048 and L. gasseri IPLA20136 in mono-culture and co-culture. Significant differences between mono-cultures and co-cultures are indicated with different letters (p-value < 0.05).

Figure 3

Growth of 2′FL-non-degrader bifidobacteria (red bars, n = 19), and 2′FL-degrader bifidobacteria (green bars, n = 19) in mono-cultures and co-cultures with three selected lactobacilli strains in the presence of 2′FL. (A) Optical density (OD_{600 nm}) and (B) pH decrease after 24 h of incubation. “L1” L. gasseri IPLA20136; “L2” L. gasseri IPLA20126; ”L3” L. paracasei IPLA20124. “Control”: mono-culture of bifidobacteria without added carbon source.

Figure 4

Intracellular and extracellular 2′FL degradation by bifidobacteria and its potential impact on lactobacilli growth in co-culture.