Enzymatic analyses demonstrate thermal adaptation of α-glucosidase activity in starch amended gully waste.

In this study we investigated the effect of starch amendment on α-glucosidase activity in an organic waste environment, treated under both mesophilic and thermophilic conditions. The relative effects of temperature on α-glucosidase activity with regard to in situ and assay conditions were investigated under a reciprocal design. The decline in dry matter under the different thermal regimes was consistent with the temperature independent degradation of starch. The results of extra-cellular enzyme analysis showed a significant relationship between starch addition and α-glucosidase activity, with evidence of thermal adaptation to the in situ temperature. A weaker, but significant, effect of starch addition on ß-glucosidase activity was observed, with no evidence for thermal adaptation. Thus, our data is consistent with a substrate adaptive response to temperature, albeit under potentially a high selective pressure.

Investigating microbial activities during a starch-amended co-composting process at mesophilic and thermophilic temperatures.

The aim of this study was to assess the use of functional microbial ecological techniques in detailing processes during composting. Using starch as an amendment for a co-composting process, small-scale individual mesocosms were investigated at two temperatures, 30 degrees C and 60 degrees C, over a five-week period. In order to determine the more exact processes occurring during degradation, extracellular enzyme analysis (EEA) and community-level physiological profiling (CLPP) were used. The EEA demonstrated that, although assay temperature effects were present, no significant difference between the two in situ composting temperatures was observed for the two enzyme substrates, alpha- and beta-glucosidase, used. The CLPP profiling was only performed on the 30 degrees C compost samples. These analyses indicated a dynamic, but broadly predictable, environment, suggesting that the use of this approach may be further applicable to these types of study. By investigating both total dry and organic weights, no difference in organic matter degradation between the two temperatures was observed. These results showed that either starch degradation acted independently of temperature or compensatory effects occurred. The former hypothesis was supported by a second experiment investigating starch degradation at both temperatures with appropriate negative controls. Trying to reconcile the EEA results with the changes in total matter was difficult without making speculative assumptions. The study highlights the need to further develop and evaluate these microbial ecological techniques to address such problems.

Analysis of bacterial activity, biomass and diversity during windrow composting.

Two contrasting compost windrows were monitored for various physical, chemical and microbiological parameters for a period of 106 days. The different input materials and management practises gave rise to different temperature, moisture, and oxygen consumption profiles as composting proceeded. However, despite the different composting conditions, the specific respiratory activity, as determined by oxygen consumption per bacterial cell, was remarkably similar for both windrows. Further investigations into diversity dynamics were done through DGGE and cloning and sequencing of bacterial 16S rDNA PCR products. Although sequence analysis showed differing bacterial communities across time and between the different windrows, similarities in the progression were noted. The majority of sequences recovered from the first sampling period (day 1) were highly similar to previously isolated organisms. The clone libraries from the last sampling period (day 106) contained organisms that showed lower homology to their closest relatives, often with other uncultured organisms, and in phyla that contain few cultured representatives. These data suggest that specific respiratory activity may be an important driver of bacterial diversity in composting environments.

Composting of green waste: observations from windrow trials and bench-scale experiments.

The composting of green waste is currently of great importance to the waste industry. For this reason, large-scale compost windrows were investigated and the results compared with those from small, bench-scale experiments. In the two windrows sampled, temperature profiles differed, and greater organic matter loss was observed in the higher temperature windrow. However, enhanced organic matter degradation through elevated temperatures was not supported in the bench-scale experiment, where, under fixed temperatures (30 and 50 degrees C, respectively), no difference in both the total dry and organic matter content was observed. Analysis of particle size distributions in both sets of experiments strongly suggested that moisture-dependent effects were a confounding factor in determining the total LOI of the windrows. Analysis of beta-glucosidase activity in the bench-scale samples demonstrated that it was the assay temperature, rather than the in situ composting temperature, which was more important in determining the level of activity. No evidence for adaptation to local maxima due to variation in the thermal environment was observed.

Investigating microbial activities in compost using mushroom (Agaricus bisporus) cultivation as an experimental system.

Investigations into the dynamic nature of composting environments are necessary to understand and ultimately optimise the complex processes that occur. In this study, various parameters were measured to investigate physical, chemical and biological changes that occur in compost during the production of Agaricus bisporus. In addition to monitoring the compost samples during mushroom cultivation, uninoculated samples were maintained for comparative purposes. Principal components analysis of the variables measured showed a clear distinction between the thermophilic Phase I composts, uninoculated Phase II composts and mushroom inoculated composts. Leucine assimilation, a novel technique to composting environments, is presented as suitable method for assessing microbial activity in such systems. Strict agreement between leucine assimilation and fluorescein diacetate (FDA) hydrolysis, a rarely used technique in composting environments, was not observed, suggesting that neither should be used as a sole measure of microbial activity in compost. Association of FDA hydrolysis with the culturable heterotrophic count suggests that FDA hydrolysis may indicate bacterial as opposed to total microbial activity.

Field evidence for density-dependent facilitation amongst Ixodes ricinus ticks feeding on sheep.

Engorged Ixodes ricinus nymphs collected from sheep resident in an upland UK field site were significantly lighter than nymphs that engorged on previously tick-naïve sheep, indicating that site-resident sheep continually exposed to ticks acquired anti-tick resistance. The weights of engorged nymphs that fed on naturally tick-resistant sheep increased significantly, however, when increasingly high numbers of adult female ticks fed on the sheep during seasonal peaks of tick activity. This relationship was unaffected by variations in nymph weight amongst individual sheep, between seasons and years, and potential effects of sheep infection with Ehrlichia phagocytophila; this suggests that high adult tick infestations may directly inhibit the expression of acquired anti-tick resistance by sheep. The length, width and weight of adult ticks and the scutum length of adult females were linearly related to their weight as an engorged nymph. The mean scutum length of adult female ticks feeding on sheep in the field site was greater than that of adult females obtained from engorged nymphs collected from sheep of the same site. This suggests that larger ticks have a survival advantage and that I. ricinus ticks exhibit density-dependent intraspecific facilitation at high infestation levels with potential consequences for the transmission of tick-borne diseases.

Natural Ehrlichia phagocytophila transmission coefficients from sheep 'carriers' to Ixodes ricinus ticks vary with the numbers of feeding ticks.

In a longitudinal study in a UK upland site, 38% of adult sheep were detected as infected with the tick-borne bacterium Ehrlichia phagocytophila by PCR of blood samples. Infection prevalence declined significantly with sheep age but varied significantly and non-linearly with the number of adult Ixodes ricinus ticks feeding per sheep. These findings suggested that under conditions of natural repeated tick-borne challenge sheep remain partially susceptible to re-infections, but the likelihood of re-infection depended on the numbers of feeding ticks. Transmission efficiency from sheep to immature ticks also varied significantly and non-linearly with the number of adult ticks feeding per sheep: transmission efficiency was almost zero in sheep with low adult tick infestations rising to 30% at certain levels of adult tick infestation. Infection intensity in infected engorged immature ticks also varied with the number of adult ticks feeding per sheep, but neither prevalence nor intensity of infection in engorged ticks were related to sheep blood PCR result. These findings suggest that variation in the numbers of ticks feeding per sheep may influence E. phagocytophila transmission by direct effects on transmission at the tick-host interface.