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.

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.

Microbial community changes during the bioremediation of creosote-contaminated soil.

AIMS: To investigate the effects of aeration on the ex situ biodegradation of polycyclic aromatic hydrocarbons (PAHs) in creosote-contaminated soil and its effect on the microbial community present. METHODS AND RESULTS: Aerated and nonaerated microcosms of soil excavated from a former timber treatment yard were maintained and sampled for PAH concentration and microbial community changes by terminal restriction fragment length polymorphism (TRFLP) analysis. After an experimental period of just 13 days, degradation was observed with all the PAHs monitored. Abiotic controls showed no loss of PAH. Results unexpectedly showed greater loss of the higher molecular weight PAHs in the nonaerated control. This may have been due to the soil excavation causing initial decompaction and aeration and the resulting changes caused in the microbial community composition, indicated by TRFLP analysis showing several ribotypes greatly increasing in relative abundance. Similar changes in both microcosms were observed but with several possible key differences. The species of micro-organisms putatively identified included Bacilli, pseudomonad, aeromonad, Vibrio and Clostridia species. CONCLUSIONS: Excavation of the contaminated soil leads to decompaction, aeration and increased nutrient availability, which in turn allow microbial biodegradation of the PAHs and a change in the microbial community structure. SIGNIFICANCE AND IMPACT OF THE STUDY: Understanding the changes occurring in the microbial community during biodegradation of all PAHs is essential for the development of improved site remediation protocols. TRFLP allows useful monitoring of the total microbial community.

THE PHYSIOLOGY OF BASIDIOMYCETE LINEAR ORGANS: I. PHOSPHATE UPTAKE BY CORDS AND MYCELIUM IN THE LABORATORY AND THE FIELD.

Phosphate uptake as a function of external medium concentration has been determined for mycelium grown in the laboratory, segments of cords collected from the field and cords in the field for a range of wood-decay basidiomycetes. Hofstee plots in all cases can be interpreted as indicating the presence of two uptake systems. Uptake of phosphate by mycelium is reduced by increasing the concentration of phosphate in the growth medium from 10 µM to 10 mM. The major portion absorbed by cords in the field remains within the segment exposed to radioactive solution, suggesting conversion of the phosphate to an immobile form unavailable for translocation.

SALT TOLERANCE IN THE HALOPHYTE SUAEDA MARITIMA (L.) DUM.: THE EFFECT OF SALINITY ON THE CONCENTRATION OF SODIUM IN THE XYLEM.

Rates of ion transport and transpiration were measured during the day and night in whole seedlings of Suaeda maritima growing over a range of salinities, in order to calculate concentrations of sodium and potassium in the xylem during these periods. Mean sodium concentration in the xylem was maximal at 56 mol m-3 Na with an external salinity of 200 mol m-3 NaCl. The sodium concentration in the xylem was greater in the dark than in the light at all external salinities investigated. Comparison of the external sodium with that in the xylem indicated that sodium was more strongly excluded from the transpiration stream as salinity increased. The mean concentration of potassium in the xylem declined as external NaCl concentration increased, although selectivity for potassium increased at higher salinities. Results are discussed in relation to osmotic adjustment in S. maritima.