Lactobacilli Are Prominent Members of the Microbiota Involved in the Ruminal Digestion of Barley and Corn

Abstract

The chemical composition of barley grain can vary among barley varieties (Fibar, Xena, McGwire, and Hilose) and result in different digestion efficiencies in the rumen. It is not known if compositional differences in barley can affect the microbiota involved in the ruminal digestion of barley. The objective of this study was to characterize the in situ rumen degradability and microbiota of four barley grain varieties and to compare these to corn. Three ruminally cannulated heifers were fed a low (60% barley silage, 37% barley grain, and 3% supplement) or high grain (37% barley silage, 60% barley grain, and 3% supplement) diet. One set of bags was used to estimate dry matter (DM), starch and crude protein (CP) degradability. A second set was used to extract DNA from the adherent microbiota and visualize grain after incubation using scanning electron microscopy (SEM). DNA was subjected to amplicon 16S rRNA gene sequencing followed by analysis using QIIME. In the low grain diet, McGwire had the highest effective degradability (ED) of DM (P < 0.01). The ED of starch was highest (P < 0.01) for Fibar, McGwire, and Xena, but the ED of CP was not affected by variety. For the high grain diet, Xena and McGwire had the highest ED of DM (P < 0.01). The ED of starch was highest (P < 0.01) for Xena and Fibar. The ED of protein was highest (P < 0.01) for Xena and McGwire. Although the microbiota did not differ among barley varieties, they did differ from corn and with incubation time. Lactobacilli were dominant members of the mature biofilms associated with corn and barley and were accompanied by a notable increase in the lactic acid utilizing genera, Megasphaera. As none of the cattle exhibited subclinical or clinical acidosis during the study, our results suggest that lactobacilli play a more prominent role in routine starch digestion than presently surmised.

Keywords: barley; biofilm; cattle; corn; microbiome; rumen; starch digestion.

FIGURE 1

In situ percent DM (A,B), starch (C,D), and protein (E,F) disappearance at six different ruminal incubation times when heifers were fed a low and high grain diet.

FIGURE 2

Alpha diversity measures of Chao1, observed species, PD whole tree, and Shannon diversity index associated with biofilms on the surface of corn (n = 6) and barley (n = 6) incubated in the rumen of heifers fed a low (A) or high grain (B) diet.

FIGURE 3

Principle coordinate analysis (PCoA) plots of the unweighted UniFrac distances for biofilm associated bacteria on corn and four barley grain varieties in heifers fed a low grain diet (A) corn and four barley varieties, (B) sampling time and (C) heifer.

FIGURE 4

Differentially abundant genera associated with barley grain after 2, 4, and 12 h incubation in the rumen of heifers fed a low grain diet from LEfSe analysis. With a log LDA score above 2.00. Lower case letter before taxonomy indicates phylum (p_), family (f_), or genus (g_).

FIGURE 5

The lactic acid-utilizing bacteria (A,B) and Lactobacillus (C) associated with the biofilms on grains incubated for different times in heifers fed a low grain diet. Lower case letter before taxonomy indicates phylum (p_) or genus (g_).

FIGURE 6

Fifteen most abundant genera within the bacterial biofilm communities associated with corn and four barley varieties incubated in the rumen of heifers fed a low grain diet for (A) 2 h, (B) 4 h, or (C) 12 h. Lower case letter before taxonomy indicates phylum (p_), family (f_), order (o_), or genus (g_).

FIGURE 7

Comparison of corn and barley grain associated biofilms illustrating an increase in the abundance select genera after (A) 2 h, (B) 4 h, and (C) 12 h of incubation in the rumen of heifers fed a low grain diet. LEfSe analysis used a log LDA score above 2.00. Lower case letter before taxonomy indicates phylum (p_), family (f_), order (o_), or genus (g_).

FIGURE 8

Fifteen most abundant genera within the bacterial biofilm communities associated with corn and four barley varieties incubated in the rumen of heifers fed a high grain diet for (A) 2 h, (B) 4 h, or (C) 12 h. Differing durations of incubation in the rumen of heifers fed a high grain diet. Lower case letter before taxonomy indicates phylum (p_), family (f_), order (o_), or genus (g_).

FIGURE 9

Rumen bacterial biofilms on the surface of grains as viewed using scanning electron microscopy (SEM) after 2, 4, and 12 h of ruminal incubation. (A) Fibar at 2 h. (B) McGwire at 2 h. (C) Fibar at 4 h. (D) McGwire at 4 h. (E) Fibar at 12 h. (F) McGwire at 12 h.