Bacterial community associated with ensilage process of wilted guinea grass

Aims: To determine the effects of wilting, storage period and bacterial inoculant on the bacterial community and ensiling fermentation of guinea grass silage. Methods and Results: Fermentation products, colony counts and denaturing gradient gel electrophoresis (DGGE) profiles were determined. There was more lactic acid than acetic acid in all silages, but the lactic acid to acetic acid ratio decreased with storage time. This shift from lactic to acetic acid was not prevented even with a combination of wilting and bacterial inoculant. The DGGE analyses suggest that facultatively heterofermentative lactic acid bacteria (Lactobacillus plantarum, Lactobacillus brevis and Lactobacillus pentosus) were involved in the shift to acetic acid fermentation. Conclusions: Lactic acid can dominate the fermentation in tropical grass silage with sufficient wilting prior to ensiling. Prolonged storage may lead to high levels of acetic acid without distinctive changes in the bacterial community. Significance and Impact of the Study: The bacterial community looks stable compared to fermentation products over the course of long storage periods in tropical grass silage. Acetic acid fermentation in tropical grass silage can be a result of the changes in bacterial metabolism rather than community structure.     

An investigation into the sources of lactic acid bacteria in grass silage

During the 1983 silage making season an investigation was carried out to determine the contribution made by farm machinery to the numbers of lactic acid bacteria present on grass. Although no lactic acid bacteria were isolated from the standing crop, up to 10³/g were found in the grass as it entered the clamp. Examination of machinery in close contact with the grass revealed lactic acid bacteria on the mower blades and on the forks of the rough-terrain vehicle used to pack the grass into the clamp. During the 1984 season the occurrence of lactic acid bacteria in particular batches of grass from the standing crop through to silage after 2 d in the clamp was studied. There was a gradual increase in numbers of lactic acid bacteria in the grass during the process of mowing and collection. Wilting resulted in a greater initial increase in numbers but non-wilted silage had the highest count after 48 h. The majority of organisms isolated from machinery before silage making were streptococci. After silage making the number and proportions of organisms changed, with numbers increasing in all cases, particularly from the mower with lactobacilli and streptococci predominating which indicates that passage through the machinery served to inoculate the grass.     

The effect of temperature and Lactobacillus amylovorus and Lact. plantarum, applied at ensiling, on wheat silage

The effects of applying Lactobacillus plantarum and Lact. amylovorus at ensiling on wheat silage stored at 25 and41 °C was studied under laboratory conditions. The inoculants were applied at 10⁶ cfu g⁻¹.Silages with no additives served as controls. Three jars per treatment were sampled on days 2, 8 and 60 after ensiling, for chemical and microbiological analyses. After the ensiling period, the silages were subjected to an aerobic stability test. The control and Lact. plantarum inoculated wheat fermented faster at 25 than at 41 °C, whereas silages inoculated with Lact. amylovorus fermented faster at 41 °C. This was apparent from the rate of pH decrease and from the contents of residual sugars and lactic acid in the final silages. The numbers of lactobacilli in the control and Lact. plantarum silages at 41 °C after 2 and 8 days of ensiling were lower than in the corresponding silages at 25 °C. For the Lact. amylovorus silage the opposite held true. The control silages at both temperatures and the Lact. plantarum silage at 41 °C were the most stable silages under aerobic exposure.     

Evaluation of the effects of dietary particle fractions on fermentation profile and concentration of microbiota in the rumen of dairy cows fed grass silage-based diets

The study evaluated the effects of three different theoretical particle lengths (TPL) of grass silage on the distribution of particle fractions of the diet and the resulting effects on fermentation profile and concentrations of protozoa and mixed bacterial mass in the rumen of three lactating Holstein cows fed total mixed rations (45% grass silage, 5% grass hay and 50% concentrate) ad libitum. Decreasing TPL of grass silage (long, medium, short) reduced particles retained on the 19-mm sieve of the Penn State Particle Separator, while particle fractions from 8 mm to 19 mm and smaller than 8 mm were increased. Different TPL did not affect pH and the concentration of volatile fatty acids in the rumen. However, lowering the TPL from long to medium increased significantly the bicarbonate concentration, acetate proportion and protozoal number in the rumen, whereas the proportion of bacterial protein in ruminal digesta and its amino acid concentration were significantly increased by the short TPL. For the current feeding conditions, it can be concluded that increasing the fraction of particles between 8 and 19 mm and probably even the fraction below 8 mm by decreasing TPL of grass silage do not adversely affect rumen conditions and can be beneficial in terms of optimising concentration and activity of ruminal microbiota in high-yielding dairy cows.     

Bacterial community dynamics during the ensilage of wilted grass

Aims:  Grass silage is the product formed by a natural lactic acid bacterial fermentation when grass is stored under anaerobic conditions, and represents an important ruminant feedstuff on farms during winter. Of the two commonly employed methods of ensiling forage, baled silage composition frequently differs from that of comparable precision-chop silage reflecting a different ensiling environment. The aim of this study was to investigate the dynamics of the silage fermentation in wilted grass and between ensiling systems.
Methods and Results:  Fermentation dynamics were examined using traditional methods of silage analyses, including microbial enumeration and analysis of fermentation products, and culture-independent terminal restriction fragment length polymorphism (T-RFLP). A successful fermentation was achieved in both systems, with the fermentation (increase in lactic acid bacteria and lactic acid concentration, decrease in pH) proceeding rapidly once the herbage was ensiled.
Conclusions:  Under controlled conditions, little difference in silage quality and microbial composition were observed between ensiling systems and this was further reflected in the T-RFLP community analysis.
Significance and Impact of the Study:  T-RFLP proved a potentially useful tool to study the ensilage process and could provide valid support to traditional methods, or a viable alternative to these methods, for investigating the dynamics of the bacterial community over the course of the fermentation.     

Evaluation of the effects of dietary particle fractions on fermentation profile and concentration of microbiota in the rumen of dairy cows fed grass silage-based diets

The study evaluated the effects of three different theoretical particle lengths (TPL) of grass silage on the distribution of particle fractions of the diet and the resulting effects on fermentation profile and concentrations of protozoa and mixed bacterial mass in the rumen of three lactating Holstein cows fed total mixed rations (45% grass silage, 5% grass hay and 50% concentrate) ad libitum. Decreasing TPL of grass silage (long, medium, short) reduced particles retained on the 19-mm sieve of the Penn State Particle Separator, while particle fractions from 8 mm to 19 mm and smaller than 8 mm were increased. Different TPL did not affect pH and the concentration of volatile fatty acids in the rumen. However, lowering the TPL from long to medium increased significantly the bicarbonate concentration, acetate proportion and protozoal number in the rumen, whereas the proportion of bacterial protein in ruminal digesta and its amino acid concentration were significantly increased by the short TPL. For the current feeding conditions, it can be concluded that increasing the fraction of particles between 8 and 19 mm and probably even the fraction below 8 mm by decreasing TPL of grass silage do not adversely affect rumen conditions and can be beneficial in terms of optimising concentration and activity of ruminal microbiota in high-yielding dairy cows.     

Influence of the maize silage to grass silage ratio and feed particle size of rations for ruminants on the community structure of ruminal Firmicutes in vitro

Aims: To investigate the effect of the forage source and feed particle size (FPS) in ruminant rations on the composition of the ruminal Firmicutes community in vitro. Methods and Results: Three diets, varying in maize silage to grass silage ratio and FPS, were incubated in a rumen simulation system. Microbial samples were taken from the liquid fermenter effluents. Microbial community analysis was performed by 16S rRNA‐based techniques. Clostridia‐specific single‐strand conformation polymorphism profiles revealed changes of the community structure in dependence on both factors tested. The coarse grass silage–containing diets seemed to enhance the occurrence of different Roseburia species. As detected by real‐time quantitative PCR, Ruminococcus albus showed a higher abundance with decreasing FPS. A slightly lower proportion of Bacilli was found with increasing grass silage to maize silage ratio by fluorescence in situ hybridization (FISH). In contrast, a slightly higher proportion of bacterial species belonging to the Clostridium‐clusters XIV a and b was detected by FISH with increasing grass silage contents in the diet. Conclusions: The ruminal Firmicutes community is affected by the choice of the forage source and FPS. Significance and Impact of the Study: This study supplies fundamental knowledge about the response of ruminal microbial communities to changing diets. Moreover, the data suggest a standardization of grinding of feeds for in vitro studies to facilitate the comparison of results of different laboratories.     

Microbial community structure in anaerobic co-digestion of grass silage and cow manure in a laboratory continuously stirred tank reactor

The impacts of feeding ratio and loading rate on the microbial community during co-digestion of grass silage with cow manure in an anaerobic laboratory continuously stirred tank reactor were investigated by 16S rRNA gene-based fingerprints. The microbial community remained stable when the reactor was fed with cow manure alone and with up to 20% of grass silage in feedstock at an organic loading rate (OLR) of 2 kg VS m⁻³ day⁻¹. Large changes in the bacterial community were observed when the loading ratio of grass was increased to 40%, while there was little change in the archaeal community. During the increase in OLR from 2 to 4 kg VS m⁻³ day⁻¹ the bacterial community structure showed few differences, whereas Archaea was undetectable. Sequencing of the major DGGE bands indicated that the phylum Bacteriodetes predominated in the bacterial community. Two unclassified bacteria with high abundance survived throughout the operation of the reactor.     

Grass and lupin silage in rations for beef steers supplemented with barley or potatoes

Twenty-eight Simmental-cross steers weighing 200 (± 20.5) kg were used to evaluate grass and whole plant lupin silages in terms of growth rate, dry matter (DM) intake and carcass characteristics. The chemical composition of the silages was determined and Dacron bag procedures were used to estimate DM and protein degradability. The silages were supplemented with either rolled barley or crushed potato. The lupin silage had a lactic acid fermentation with lower DM, neutral detergent fiber (NDF) and protein nitrogen than the grass silage but higher crude protein. There were no statistically significant differences in gain, carcass weight, dressing percentage or backfat levels between steers fed lupin or grass silage. DM intake of the silages was not significantly different but there was a tendency for lower DM intake of lupin silage when supplemented with potatoes. There was no difference in DM degradability between lupin and grass silages. Lupin nitrogen degraded at a significantly faster rate (24.5% h⁻¹) compared with the grass (10.4% h⁻¹). The effective degradation of nitrogen at a ruminal fractional outflow rate of 0.05 h⁻¹ was 63.8% and 79.1% for grass and lupin silage, respectively. Ensiling whole plant lupin can produce a high quality silage for use in beef rations.     

Effects of silage from maize crops differing in maturity at harvest,grass silage feed value and concentrate feed level on performance of finishing lambs

The effects of (i) medium and high feed value (MFV and HFV) maize silages and (ii) MFV and HFV grass silages, each in combination with a range of concentrate feed levels, on the performance of finishing lambs were evaluated using 280 Suffolk-X lambs (initial live weight 36.1 kg). The MFV and HFV maize silages represented crops with dry matter (DM) concentrations of 185 and 250 g/kg, respectively, at harvest, and had starch and metabolisable energy (ME) concentrations of 33 and 277 g/kg DM and 9.6 and 11.0 MJ/kg, respectively. HFV and MFV grass silages had DM and ME concentrations of 216 and 294 g/kg and 11.0 and 11.5 MJ/kg DM, respectively. A total of 13 treatments were involved. The four silages were offered ad libitum with daily concentrate supplements of 0.2, 0.5 or 0.8 kg per lamb. A final treatment consisted of concentrate offered ad libitum with 0.5 kg of the HFV grass silage daily. Increasing the feed value of grass silage increased (P < 0.001) forage intake, daily carcass and live weight gains, final live weight and carcass weight. Increasing maize silage feed value tended to increase (P = 0.07) daily carcass gain. Increasing concentrate feed level increased total food and ME intakes, and live weight and carcass gains. There was a significant interaction between silage feed value and the response to concentrate feed level. Relative to the HFV grass silage, the positive linear response to increasing concentrate feed level was greater with lambs offered the MFV grass silage for daily live weight gain (P < 0.001), daily carcass gain (P < 0.01) and final carcass weight (P < 0.01). Relative to the HFV maize silage, there was a greater response to increasing concentrate feed level from lambs offered the MFV maize silage in terms of daily carcass gain (P < 0.05) and daily live weight gain (P = 0.06). Forage type had no significant effect on the response to increased concentrate feed level. Relative to the MFV grass silage supplemented with 0.2 kg concentrate, the potential concentrate-sparing effect of the HFV grass silage, and the MFV and HFV maize silages was 0.41, 0.09 and 0.25 kg daily per lamb, respectively. It is concluded that increasing forage feed value increased forage intake and animal performance, and maize silage can replace MFV grass silage in the diet of finishing lambs as performance was equal to or better (depending on maturity of maize at harvest) than that for MFV grass silage.     

Cold stress-induced changes in the aerobic heterotrophic gastrointestinal tract bacterial flora of red hybrid tilapia

Fifteen juvenile red hybrid tilapia Oreochromis mossambicus × O. macrochir averaging 50 g body weight were cold-stressed by immersion in 18° C sea water; control fish ( n = 15) were kept at the acclimation temperature of 26° C. Three fish from each group were killed 0, 24, 48 and 72 h after the start of the experiment. Gastrointestinal tracts were removed and dissected into the stomach, anterior gut and posterior gut regions. Aerobic heterotrophic bacteria were identified and enumerated relative to temperature, exposure time and gastrointestinal tract region. Gram negative genera included Alcaligenes, Flavobacterium, Photobacterium, Pseudomonas and Vibrio ; the latter three were predominant. Mean bacterial numbers and taxonomic composition of the microflora varied significantly ( P <0·05) in response to the three test variables. There were greater mean total bacterial numbers at 18 than at 26° C, due primarily to proliferation of Vibrio spp. Mean bacterial numbers after 24 h were greater than those at both the earlier and later sampling periods. Mean bacterial numbers in the stomach were less than those in the anterior and posterior gut, which were not significantly different. The relative abundance of Vibrio spp. was negatively correlated with that of Flavobacterium , which may have reflected competition between pathogenic and nonpathogenic species. Such stress-induced changes in the bacterial microflora may contribute to the onset of disease because several species of Vibrio are known primary or opportunistic fish pathogens.     

Digestion, rumen fermentation and circulating concentrations of insulin, growth hormone and IGF-1 in steers fed diets based on different proportions of maize silage and grass silage

Replacing grass silage with maize silage results in a fundamental change in the ratio of structural to non-structural carbohydrates with commensurate changes in rumen fermentation patterns and nutrient utilisation. This study investigated the effects of feeding four forage mixtures, namely grass silage (G); 67 g/100 g grass silage + 33 g/100 g maize silage (GGM); 67 g/100 g maize silage + 33/100 g grass silage (MMG); maize silage (M) to four ruminally and duodenally canulated Holstein Friesian steers. All diets were formulated to be isonitrogenous (22.4 g N/kg DM) using a concentrate mixture. Dietary dry matter (DM) and organic matter (OM) digestibility increased with ascending maize silage inclusion (P < 0.1) whereas starch and neutral detergent fibre digestibility declined (P < 0.05). Ratio of non-glucogenic to glucogenic precursors in the rumen fluid increased with maize silage inclusion (P < 0.01) with a commensurate reduction in rumen pH (P < 0.05). Mean circulating concentrations of insulin were greatest and similar in diets MMG and GGM, lower in diet M and lowest in diet G (P < 0.01). There were no effects of diet on the mean circulating concentration of growth hormone (GH), or the frequency, amplitude and duration of GH pulses, or the mean circulating concentrations of IGF-1. Increasing levels of DM, OM and starch intakes with the substitution of grass silage with maize silage affected overall digestion, nutrient partitioning and subsequent circulating concentrations of insulin.     

The effect of procaine on the partitioning of plasmid pSC101

Abstract An examination of samples obtained from a commercial fish smoker, using seawater agar with incubation at 4°, 15° and 37°C for up to 28 days, revealed the presence of large bacterial populations in smoked fish. However, initially only low bacterial numbers, i.e., 2 × 10³/g, were present in the muscle of fresh, whole haddock ( Melanogrammus aeglefinus ). With filleting, there was a sudden increase in numbers to 9.2 × 10⁵/g. Yet immediately after smoking, the bacterial populations decreased (5 × 10⁵/g), followed by a gradual increase with storage (e.g., 2 × 10⁶/g after 24 h). Representative colonies were presumptively identified as Acinetobacter, Alcaligenes , coryneforms, Pseudomonas and Vibrio spp.     

The response of sheep to big bale grass silage ensiled with,or supplemented separately with,molassed sugar beet feed

Second cut big bale grass silage was prepared with grass ensiled alone or with added pelleted, molassed sugar beet feed (MSBF) at 32 or 64 g MSBF kg⁻¹ fresh weight of grass. Addition of MSBF at ensilage increased silage dry matter (DM), water soluble carbohydrate and lactic acid concentrations and decreased ammonia concentration. When fed to wether lambs, MSBF addition, whether at ensilage or given separately, variably improved DM intake, live-weight gain and feed conversion efficiency. Ruminal concentrations of ammonia were reduced and acetate molar proportion increased in diets supplemented with MSBF separately compared with the silage only control diet. Animal performance was generally improved by MSBF supplementation with responses to silages made with added MSBF comparable to those from silage supplemented with MSBF at feeding. There was little difference in animal performance between silages made with 32 or 64 g kg⁻¹ MSBF added at ensiling.     

Assessing the impact of various ensilage factors on the fermentation of grass silage using conventional culture and bacterial community analysis techniques

Aims: Grass silage is an important ruminant feedstuff on farms during winter. The ensilage of grass involves a natural lactic acid bacterial fermentation under anaerobic conditions, and numerous factors can influence the outcome of preservation. The aim of this study was to investigate the effect of dry matter concentration, ensiling system, compaction and air infiltration on silage bacterial community composition. Methods and Results: The impact of these factors was examined using conventional methods of microbial analysis and culture‐independent Terminal Restriction Fragment Length Polymorphism (T‐RFLP). Silage fermentation was restricted in herbage with a high dry matter concentration, and this was reflected in a shift in the bacterial population present. In contrast, ensiling system had little effect on bacterial community composition. Air infiltration, in the absence of compaction, altered silage bacterial community composition and silage pH. Conclusions: Dry matter concentration and the absence of compaction were the main factors affecting silage microbial community composition, and this was reflected in both the conventional culture‐based and T‐RFLP data. Significance and Impact of the Study: T‐RFLP proved a useful tool to study the factors affecting ensilage. Apart from monitoring the presence or absence of members of the population, shifts in the relative presence of members could be monitored.     

The bactericidal, fungicidal and sporicidal properties of hydrogen peroxide and peracetic acid

The antimicrobial properties of aqueous solutions of peracetic acid and hydrogen peroxide have been compared. Peracetic acid exhibited excellent antimicrobial properties, especially under acidic conditions. Reductions by a factor of 10⁶ in the numbers of vegetative bacteria are obtained within 1 min at 25°C using a solution containing 1.3 mmol/l of peracetic acid. Rapid activity against bacterial spores and yeasts also occurs. Hydrogen peroxide is more effective as a sporicide than as a bactericide, with sporicidal action being obtained using a solution containing 0.88 mol/l. Bactericidal action is poor but hydrogen peroxide was bacteriostatic at concentrations above 0.15 mmol/l.     

Changes in Rumen Microbial Community Composition during Adaption to an In Vitro System and the Impact of Different Forages

This study examined ruminal microbial community composition alterations during initial adaption to and following incubation in a rumen simulation system (Rusitec) using grass or corn silage as substrates. Samples were collected from fermenter liquids at 0, 2, 4, 12, 24, and 48 h and from feed residues at 0, 24, and 48 h after initiation of incubation (period 1) and on day 13 (period 2). Microbial DNA was extracted and real-time qPCR was used to quantify differences in the abundance of protozoa, methanogens, total bacteria, Fibrobacter succinogenes, Ruminococcus albus, Ruminobacter amylophilus, Prevotella bryantii, Selenomonas ruminantium, and Clostridium aminophilum. We found that forage source and sampling time significantly influenced the ruminal microbial community. The gene copy numbers of most microbial species (except C. aminophilum) decreased in period 1; however, adaption continued through period 2 for several species. The addition of fresh substrate in period 2 led to increasing copy numbers of all microbial species during the first 2–4 h in the fermenter liquid except protozoa, which showed a postprandial decrease. Corn silage enhanced the growth of R. amylophilus and F. succinogenes, and grass silage enhanced R. albus, P. bryantii, and C. aminophilum. No effect of forage source was detected on total bacteria, protozoa, S. ruminantium, or methanogens or on total gas production, although grass silage enhanced methane production. This study showed that the Rusitec provides a stable system after an adaption phase that should last longer than 48 h, and that the forage source influenced several microbial species.     

Effect of the corn silage to grass silage ratio and feed particle size of diets for ruminants on the ruminal Bacteroides-Prevotella community in vitro

This study examined whether different corn silage to grass silage ratios in ruminant rations and different grinding levels of the feed affect the composition of the ruminal Bacteroides-Prevotella community in vitro. Three diets, composed of 10% soybean meal as well as of different corn silage and grass silage proportions, were ground through 1 mm or 4 mm screened sieves and incubated in a semi-continuous rumen simulation system. On day 14 of the incubation microbes were harvested by centrifugation from the liquid effluent of fermenter vessels. Microbial DNA was extracted for single strand conformation polymorphism (SSCP) analysis of 16S rRNA genes followed by sequencing of single SSCP bands. Fluorescence in situ hybridization (FISH) and real-time quantitative (q) PCR were used to quantify differences in the relative abundance of Bacteroides-Prevotella and Prevotella bryantii. SSCP profiles revealed a significant influence of the forage source as well as of the feed particle size on the community structure of the Bacteroides-Prevotella group. Different, phylogenetically distinct, so far uncultured Prevotella species were detected by sequence analysis of several treatment-dependent occurring SSCP bands indicating different nutritional requirements of these organisms for growth. No quantitative differences in the occurrence of Bacteroides-Prevotella-related species were detected between diets by FISH with probe BAC303. However, real-time qPCR data revealed a higher abundance of P. bryantii with increasing grass silage to corn silage ratio, thus again indicating changes within the community composition of the Bacteroides-Prevotella group. As P. bryantii possesses high proteolytic activity its higher abundance may have been caused by the higher contents of crude protein in the grass silage containing diets. To conclude, results of this study show an influence of the forage source on the ruminal community of Bacteroides-Prevotella. Furthermore, they suggest an effect of the feed particle size on this bacterial group.     

Effects of replacing grass silage with either maize or whole-crop wheat silages on the performance and meat quality of beef cattle offered two levels of concentrates

A randomised design involving 66 continental cross beef steers (initial live weight 523 kg) was undertaken to evaluate the effects of the inclusion of maize or whole-crop wheat silages in grass silage-based diets on animal performance, carcass composition, and meat quality of beef cattle. Grass silage was offered either as the sole forage or in addition to either maize or whole-crop wheat silages at a ratio of 40:60, on a dry matter (DM) basis, alternative forage: grass silage. For the grass, maize, and whole-crop wheat silages, DM concentrations were 192, 276, and 319 g/kg, ammonia-nitrogen concentrations were 110, 90, and 150 g/kg nitrogen, starch concentrations were not determined, 225, and 209 g/kg DM and in vivo DM digestibilities were 0.69, 0.69, and 0.58; respectively. The forages were offered ad libitum following mixing in a paddle type complete diet mixer wagon once per day, supplemented with either 3 or 5 kg concentrates per steer per day, in two equal feeds, for 92 days. For the grass, grass plus maize and grass plus whole-crop wheat silage-based diets food intakes were 8.38, 9.08, and 9.14 kg DM per day, estimated carcass gains were 514, 602, and 496 g/day and carcass weights were 326, 334, and 325 kg; respectively. Altering the silage component of the diet did not influence carcass composition or meat eating quality. Increasing concentrate feed level tended ( P = 0.09) to increase estimated carcass fat concentration and increased sarcomere length ( P < 0.05), and lean a* ( P < 0.01), b* ( P < 0.05), and chroma ( P < 0.01). There were no significant silage type by concentrate feed level interactions for food intake, steer performance, carcass characteristics or meat eating quality. It is concluded that replacing grass silage with maize silage increased carcass gain, and weight due to higher intakes, and improved utilisation of metabolisable energy. Whilst replacing grass silage with whole-crop wheat silage increased live-weight gain, the reduced dressing proportion resulted in no beneficial effect on carcass gain, probably due to increased food intakes of lower digestible forage increasing gut fill. Meat quality or carcass composition were not altered by the inclusion of maize or whole-crop silages in grass silage based diets.     

A COMPARATIVE STUDY OF LACTOBACILLI FROM GRASS SILAGE AND OTHER SOURCES

Samples of 152 strains of lacto bacilli isolated from six different types of grass silage, which had been subjected to various treatments at the time of ensiling, and five strains isolated from other sources for comparative purposes, were tested by their reactions in litmus milk, yeast extract litmus milk, dextrose litmus milk, yeast extract dextrose litmus milk and in various carbohydrate broths. The metabolic products formed from dextrose by nineteen selected strains were identified and estimated.
The evidence obtained in this way pointed to the conclusion that the majority of lactobacilli in grass silage are strains of Streptobacterium plantarum, characterized by comparative inactivity in ntmns milk, bat markedly stimulated by addition of yeast extract. They produce from dextrose mainly lactic acid (usually the inactive form) with a small quantity of acetic acid. A strain was encountered which also produced alcohol and butyric acid, but the numbers of this type in silage was negligible. Considerable differences were found in the ability of the various strains to ferment carbohydrates.
Of the five strains isolated from dairy products three woe of the Streptobacterium plantarum type and two were of a kind which rapidly clotted litmus milk and exhibited reactions corresponding to the true milk strains.
The authors wish to record their thanks to the Research Council of Imperial Chemical Industries, Ltd., for a grant which rendered this work possible, to Dr S. J. Watson for supplying samples of grass and silage, and to Dr J. 6. Davis for valuable suggestions.