Emerging resistant microbiota from an acidic soil exposed to toxicity of Cr, Cd and Pb is mainly influenced by the bioavailability of these metals

Purpose

The effect of pollutants in soil microorganisms is an important issue in order to understand their toxic effects in the environment, as well as for developing adequate bioremediation strategies. In this sense, the main objective of this study was to assess the involvement of the indigenous microbiota of an acidic forest Mediterranean soil by artificial pollution with heavy metals, and to detect and isolate resistant microorganisms that could be useful for bioremediation.

Materials and methods

Samples from a previously unpolluted acidic forest soil were amended with Cr(VI), Cd(II) or Pb(II) at total amounts ranging from 0.1 to 5,000 mg?kg^?1. These soil microcosms were incubated under controlled laboratory conditions for 28 days. Soluble fractions of metals were determined from aqueous extracts. Both activity and composition of the microbial community were assessed, respectively, by respirometric assays and molecular analysis (polymerase chain reaction denaturing gradient gel electrophoresis). The isolation of metal-resistant microorganisms was attempted by culture plating from microcosms incubated with high concentrations of metals. Isolated strains were tested in cultures with minimal medium to check for their metal resistance and their capacity to reduce the presence of toxic Cr(VI).

Results and discussion

A decrease in the soil respirometric activity and changes in the microbial community composition were detected from 10/100 mg?kg^?1 Cr and 1,000 mg?kg^?1 Cd and Pb. Presumably resistant bacterial and fungal populations developed in most of these polluted microcosms; however, the microbiota was severely impaired at the highest additions of Cr. Even though Cr was the most damaging metal in soil microcosms, if the soluble fractions of metals are considered instead of their total added amounts, the comparison among their toxic effects suggests a similar potential toxicity of Cr and Pb. Isolated multiresistant microorganisms were related mainly to Actinobacteria, Firmicutes and Ascomycota. Some of them showed the capacity to reduce Cr(VI) concentrations between 54 % and 70 % of the initial value. These strains were affiliated to several species of Streptomyces and Bacillus.

Conclusions

The combination of respirometric assays with molecular methods has been useful to assess the effect of metals on the soil microbial community, which can greatly be explained by their differential bioavailability. Cultivation-dependent and -independent approaches have proved the presence and development of multiresistant microorganisms in a previously unpolluted soil. Due to their properties, some of the isolated strains are potentially useful for soil bioremediation.     

Tenoscopy in 33 horses with septic and nonseptic digital tenosynovitis (1997–2001)

Tenoscopy is the use of an arthroscope to access tendon sheaths. This article reports clinical findings, treatments, and outcomes of 33 horses with either septic or nonseptic digital tenosynovitis submitted to 36 tenoscopies during 34 occasions at the Marion duPont Scott Equine Medical Center (1997–2001). Two of the 16 horses with septic tenosynovitis were euthanized at the hospital. From the 32 horses discharged from the hospital, outcome was obtained in 31 cases: 12 horses (6 septic) could work at the same level. No difference was detected between the outcome groups regarding clinical and laboratory variables. In nonseptic cases, lameness grade, circulating white blood cells, and plasma fibrinogen before surgery were lower, while the period between the onset of clinical signs and surgery was longer and duration of phenylbutazone treatment and hospitalization was shorter. No difference in the outcome was detected when septic and nonseptic cases were compared. Tenoscopy was useful for diagnosis and treatment of nonseptic and septic digital tenosynovitis. The small number of cases and the lack of accurate information due to the retrospective nature of the study may have prevented detection of a difference between the outcomes of horses with septic versus nonseptic tenosynovitis.     

Carcass characteristics and meat quality of lambs fed with cassava foliage hay and spineless cactus

The objective of this study was to evaluate the influence of the total or partial replacement of Tifton 85 hay (TH) by cassava foliage hay (CH) and/or spineless cactus (SC) on the carcass characteristics and meat quality of confined lambs. Thirty-five Dorper x Santa Inês crossbred lambs were used, with an initial average weight of 16.0 ± 1.9 kg, fed with five treatment diets: 70% TH, 70% CH, 35% TH + 35% CH, 35% TH + 35% SC, and 35% CH + 35% SC. After 90 days of confinement, the animals were slaughtered and the carcass and meat data were compared using the Tukey test at 5%. The partial replacement of TH by SC increased the cold carcass weight by 3.9 kg (p < .05). The proportion of fat (%) increased (p < .05) when TH was replaced by CH + SC. The intensity of red (a*) was lower (p < .05) in the meat of animals fed with CH or CH + SC. It is recommended to partially replace TH with SC, or to replace totally with CH in association with SC.     

Metabolic acidosis: a quick reference.

This article serves as a quick reference for metabolic acidosis. Guidelines for analysis and causes, signs, and a stepwise approach are presented.     

Chloride: a quick reference.

This article serves as a quick reference for the analysis of chloride abnormalities. Guidelines for causes, signs, and stepwise approaches for corrected hypochloremia and hyperchloremia are presented.     

Selection in early generations and the occurrence of heterosis for the character root distribution

Crops of bean are sensible to climate changes, especially water stress. One way to minimize this instability is through genetic breeding of root system character. Thus, the objective of this study was to identify genotypes with superior root system in the first segregating generation at three depths in the soil profile and also verify the occurrence of heterosis for the root system character. Evaluations were performed using the method of Bohm (Methods studying root systems. Springer, Berlin 1979) at three different depths (0–10, 10–20 and 20–30 cm), in the experimental area of the Institute of Molecular Genetics and Breeding, at the State University of Santa Catarina UDESC Lages-SC. Twelve segregating populations and four parents (BAF 09, BAF 07, BAF 50 and IPR Uirapuru) were assessed by comparison. The favorable genotypes to the progress of generations are: two, seven and three for depths up to 20 cm and three for depths up to 30 cm. The cross between the parents BAF 07 (black group) and BAF 50 (carioca group) presented wide genetic divergence, providing significant increase in the root system revealed by the analysis of their progenies. The selection of superior genotypes in the layer of 20–30 cm was limited because most genotypes have similar and poorly distribution. Due to the strong effect of the dominance component, heterosis occurred for root distribution in early generation. This fact may interfere in the selection of autogamous species of bean related to this genetic character.     

Soil organic carbon as a key predictor of N in forest soils of Brazil

Purpose

Despite the ancillary knowledge that soil N is chiefly retained as soil organic matter, little is known about how it is affected by other soil and environmental factors, especially in the tropics. In this study, we performed a comprehensive survey of soils under native vegetation in Minas Gerais, Brazil, aiming to (a) measure soil Kjeldahl-N concentrations to a 1-m depth, (b) identify the main affecting factors of soil N retention, and (c) predict N through soil profile based on organic C (SOC) and its main conditioning factors.

Materials and methods

Soils under 36 fragments of native forest and savanna were sampled at five depths (0–10, 10–20, 20–40, 40–60, and 60–100 cm) and characterized by physical and chemical analyses, including total N determined by the micro-Kjeldahl method. Single and multivariate regressions were used to predict N concentrations based on soil properties and climatic factors.

Results and discussion

The average N concentrations ranged between 0.12 and 7.54 g kg^?1, decreasing with depth, and can be predicted using SOC concentrations (R ² = 0.86). Multivariate regressions using more input data, namely texture, cation exchange capacity (CEC), and altitude increased slightly R ² values (0.68–0.90) for separate soil depths, but not for the whole dataset (R ² = 0.85).

Conclusions

We demonstrated that N can be adequately predicted based on SOC concentrations, for any depth and forest type. The implications of the stable SOC/N relation and their coupled cycles and the environmental factors affecting N retention in Brazilian weathered soils are further discussed.