Rapidly growing mycobacteria (RGM) are common soil saprophytes, but certain strains cause infections in human and animals. The infections due to RGM have been increasing in past decades and are often difficult to treat. The susceptibility... more
Rapidly growing mycobacteria (RGM) are common soil saprophytes, but certain strains cause infections in human and animals. The infections due to RGM have been increasing in past decades and are often difficult to treat. The susceptibility to antibiotics is regularly evaluated in clinical isolates of RGM, but the data on soil RGM are missing. The objectives of this study was to isolate RGM from four grassland soils with different impact of manuring, and assess their resistance to antibiotics and the ability to grow at 37°C and 42°C. Since isolation of RGM from soil is a challenge, a conventional decontamination method (NaOH/malachite green/cycloheximide) and a recent method based on olive oil/SDS demulsification were compared. The olive oil/SDS method was less efficient, mainly because of the emulsion instability and plate overgrowing with other bacteria. Altogether, 44 isolates were obtained and 23 representatives of different RGM genotypes were screened. The number of isolates per soil decreased with increasing soil pH, consistently with previous findings that mycobacteria were more abundant in low pH soils. Most of the isolates belonged to the Mycobacterium fortuitum group. The majority of isolates was resistant to 2-4 antibiotics. Multiresistant strains occurred also in a control soil that has a long history without the exposure to antibiotic-containing manure. Seven isolates grew at 37°C, including the species M. septicum and M. fortuitum known for infections in humans. This study shows that multiresistant RGM close to known human pathogens occur in grassland soils regardless the soil history of manuring.
Antibiotic residues and antibiotic resistance genes originating from animal waste represent environmental pollutants with possible human health consequences. In this study, we addressed the question whether chlortetracycline (CTC)... more
Antibiotic residues and antibiotic resistance genes originating from animal waste represent environmental pollutants with possible human health consequences. In this study, we addressed the question whether chlortetracycline (CTC) residues in soils can act as selective pressure enhancing the persistence of tetracycline (TC-r) resistance genes in grassland soils receiving cattle feces. We performed a soil microcosm experiment, using 3 grassland soils with different management history, which were incubated with feces from conventionally raised dairy cows. The microcosms included treatments with a low dose (0.2 mg kg1), a high dose (100 mg kg1) and no CTC. The presence and abundance of TC-r genes tet(O), tet(Q) and tet(W) and the intI1 gene coding for class 1 integrase were assessed with real-time PCR after 0, 14, 28, 56 and 86 d of incubation. The genes tet(Q) and intI1 persisted in all feces-containing treatments for at least 28 d, and tet(W) and tet(O) for at least 86 d, though they went close to limits of quantification after 14e28 d in most cases. The soil, but not the dose of CTC, significantly affected the gene persistence. Concluding, certain TC-r genes originating from cattle feces may persist in soil for several months independently from antibiotic selection pressure.
In areas used for cattle overwintering detrimental effects normally associated with grazing are intensified. Among the alterations observed, increases on the N availability and soil pH may highly influence structure of ammonia oxidizing... more
In areas used for cattle overwintering detrimental effects normally associated with grazing are intensified. Among the alterations observed, increases on the N availability and soil pH may highly influence structure of ammonia oxidizing microbes and thus influence nitrification pattern in soil. To evaluate this assumption, we assessed the abundance and diversity of ammonia oxidizing bacteria (AOB) and archaea (AOA) in three sites with different degrees of animal impact (severe, moderate or no impact) of an overwintering pasture by means of qPCR and T-RFLP of amoA genes. In areas where no animal impact could be identified AOA was dominating over AOB. However, AOB abundance increased as the degree of animal impact enhances, becoming most dominant in the severely impacted site. Interestingly, the diversity of AOB was the highest in the severely impacted area, where AOA diversity was the lowest. Obviously the pressure imposed by altered environmental conditions created by cattle husbandry lead to the selection of AOB and AOA populations, adapted to alkaline pH and higher ammonia concentration.
Abstract Fire and grazing are the two most common disturbances found in the grassland ecosystems of Cherrapunjee. There are many species that have attributes which enable them to tolerate disturbances. The present study was conducted to... more
Abstract Fire and grazing are the two most common disturbances found in the grassland ecosystems of Cherrapunjee. There are many species that have attributes which enable them to tolerate disturbances. The present study was conducted to examine separately as well as in combination the effects of fire and grazing on grassland ecosystem of Cherrapunjee. The results of the study reveal that the impact of fire and grazing on vegetation structure of grassland ecosystem at Cherrapunjee are highly variable. While grazing tends to favour the diversity of perennial grasses, fire influences the richness of annual grasses and other monocots. However, the combined effect of grazing and fire tend to increase the diversity of forbs.
In the present study, we tested the hypothesis that animal treading associated with a high input of organic matter would favour methanogenesis in soils used as overwintering pasture. Hence, methane emissions and methanogen populations... more
In the present study, we tested the hypothesis that animal treading associated with a high input of organic matter would favour methanogenesis in soils used as overwintering pasture. Hence, methane emissions and methanogen populations were examined at sections with different degree of cattle impact in a Farm in South Bohemia, Czech Republic. In spring, methane emission positively corresponded to the gradient of animal impact. Applying phospholipid etherlipid analysis, the highest archaeal biomass was found in section severe impact (SI), followed by moderate impact (MI) and no impact. The same trend was observed for the methanogens as showed by real-time quantitative PCR analyses of methyl coenzyme M reductase (mcrA) genes. The detection of monounsaturated isoprenoid side chain hydrocarbons (i20:1) indicated the presence of acetoclastic methanogens in the cattle-impacted sites. This result was corroborated by the phylogenetic analysis of mcrA gene sequences obtained from section SI, which showed that 33% of the analysed clones belonged to the genus Methanosarcina. The majority of the sequenced clones (41%) showed close affiliations with uncultured rumen archaeons. This leads to the assumption that a substantial part of the methanogenic community in plot SI derived from the grazing cattle itself. Compared to the spring sampling, in autumn, a significant reduction in archaeal biomass and number of copies of mcrA genes was observed mainly for section MI. It can be concluded that after 5 months without cattle impact, the severely impact section maintained its methane production potential, whereas the methane production potential under moderate impact returned to background values.
Managed grasslands are a predominant land use in northern temperate regions. Th ey are oft en on poorly drained soils and contain large stocks of soil organic carbon (SOC). It is important to understand C dynamics in grasslands to better... more
Managed grasslands are a predominant land use in northern temperate regions. Th ey are oft en on poorly drained soils and contain large stocks of soil organic carbon (SOC). It is important to understand C dynamics in grasslands to better assess their role in regional C budgets. Two adjacent grassland plots, one amended with 100 m3 ha−1 of liquid swine manure (LSM) annually since 1978, and another unamended were killed by glyphosate in the autumn or (i) left with vegetation intact. Those killed were either (ii) left as an undisturbed chemical fallow, (iii) plowed by full-inversion tillage (FIT) in the autumn, or (iv) in the spring. Following the autumn plowing, we monitored CO2 emissions from the fallow soil surface, CO2 concentrations in the soil profile, soil temperature, and soil water content for 1 yr. Changes in soil aggregation, the light fraction organic matter, and microbial biomass were also monitored. Plowing decreased the total microbial biomass on average by 27 g C m−2, the quantity of water-stable aggregates by 7 to 12% and with it the concentration of light fraction organic matter. Respiration was also reduced by 142 g CO2-C m−2 by autumn-FIT and 175 g CO2-C m−2 by spring-FIT on unamended soils, and 90 g CO2-C m−2 by autumn-FIT and 98 g CO2-C m−2 by spring-FIT on amended soils. Regression analyses suggested that reductions in CO2 emissions were due to the placement of surface SOC at depth where soil temperature and oxygen availability were attenuated. In these soils, the cool humid conditions at depth in the soil profile may act to counter-balance the physical effects of tillage thereby preserving C deep in the soil profile. Effective calculation of C budgets and changes in SOC stocks depends on the ability to reproduce the interaction between climate, soil type, land use, and management action. A more complete understanding of the effect of management actions that modify the vertical distribution of biogeochemical (particularly organic C) and environmental parameters on soil respiration in poorly drained soils is required.
