Metagenome analyses reveal the influence of the inoculant Lactobacillus buchneri CD034 on the microbial community involved in grass ensiling

Silage is green fodder conserved by lactic acid fermentation performed by epiphytic lactic acid bacteria under anaerobic conditions. To improve the ensiling process and the quality of the resulting silage, starter cultures are added to the fresh forage. A detailed analysis of the microbial community playing a role in grass ensiling has been carried out by high throughput sequencing technologies. Moreover, the influence of the inoculant Lactobacillus buchneri CD034 on the microbial community composition was studied. For this purpose, grass was ensiled untreated or inoculated with L. buchneri CD034. The fresh forage as well as silages after 14 and 58 days of fermentation were characterized physico-chemically. Characteristic silage conditions such as increased titers of lactic acid bacteria and higher concentrations of acetic acid were observed in the inoculated silage in comparison to the untreated samples. Taxonomic community profiles deduced from 16S rDNA amplicon sequences indicated that the relative abundance of Lactococci diminished in the course of fermentations and that the proportion of bacteria belonging to the phyla Proteobacteria and Bacteroidetes increased during the fermentation of untreated silage. In the inoculated silage, members of these phyla were repressed due to an increased abundance of Lactobacilli. In addition, metagenome analyses of silage samples confirmed taxonomic profiles based on 16S rDNA amplicons. Moreover, Lactobacillus plantarum, Lactobacillus brevis and Lactococcus lactis were found to be dominant species within silages as analyzed by means of fragment recruitments of metagenomic sequence reads on complete reference genome sequences. Fragment recruitments also provided clear evidence for the competitiveness of the inoculant strain L. buchneri CD034 during the fermentation of the inoculated silage. The inoculation strain was able to outcompete other community members and also affected physico-chemical characteristics of the silage.

The role of Lactobacillus buchneri in forage preservation

In 1996 Wienberg and Muck proposed to implement Lactobacillus buchneri in silage starters. The main reason for the use of heterofermentative lactic acid bacteria is the increased stability of silages against deterioration by yeasts and moulds when exposed to air. In the following years, the unique activity of L. buchneri in silages was evaluated. It was proven that acetic acid formed from lactic acid by L. buchneri is solely responsible for the increased stability of silages. Recently, a novel metabolic pathway from lactic acid to acetic acid and 1,2-propanediol was proposed.

Acetic acid increases stability of silage under aerobic conditions

The effects of various compounds on the aerobic stability of silages were evaluated. It has been observed that inoculation of whole-crop maize with homofermentative lactic acid bacteria leads to silages which have low stability against aerobic deterioration, while inoculation with heterofermentative lactic acid bacteria, such as Lactobacillus brevis or Lactobacillus buchneri, increases stability. Acetic acid has been proven to be the sole substance responsible for the increased aerobic stability, and this acid acts as an inhibitor of spoilage organisms. Therefore, stability increases exponentially with acetic acid concentration. Only butyric acid has a similar effect. Other compounds, like lactic acid, 1,2-propanediol, and 1-propanol, have been shown to have no effect, while fructose and mannitol reduce stability.

The aerobic stability of silages influenced by metabolites of lactic acid bacteria

The stability of silages after opening the silo depends strongly on the products formed by the microorganism flora present during the conservation process. A silage additive developed at IFA-Tulln showed best results on different crops. In the starting phase of silage fermentation, acetic acid was formed by the heterofermentative lactic acid bacteria L. brevis from sugars. In the later stages, L. buchneri converts also lactic acid into acetic acid. Several trials involving different formulations of starters with varying amounts of single homo- and heterofermentative lactic acid bacteria were tested in laboratory and clump silos. Finally, an optimum composition of lactic acid bacteria, which reliably increases aerobic stability of silages and still guaranties highest quality, was evaluated.

The classification of multiple somatoform symptoms

This study evaluated the concordance among different approaches to diagnose patients with multiple somatoform symptoms. Inpatients (N = 108) of a center for behavioral medicine were diagnosed using a structured clinical interview. Somatization disorder according to DSM-IV and ICD-10 was as rare as somatization disorder according to DSM-III-R. The overlap between the criteria of DSM and ICD for somatization disorder was lower than that between DSM-III-R and DSM-IV. Somatoform autonomic dysfunction, a diagnostic category proposed by ICD-10, included fewer patients diagnosed with somatization disorder than the criteria of Escobar and colleagues for abridged somatization disorder (SSI-4/6: this Journal 177:140-146, 1989). Therefore, the Escobar criteria may be a common link between ICD-10 and DSM-IV. Although the original Escobar criteria were built upon the symptom list of DSM-III-R somatization disorder, SSI-3/5 is an empirically derived equivalent according to DSM-IV in our study (a minimum of 3 symptoms for men or 5 symptoms for women out of the list of 33 somatization symptoms according to DSM-IV).