Heated soil-water extract effect on bacterial growth: pH or toxic compounds?

Fire-induced soil changes influence indirectly on soil microbial response, mainly due to pH increases and organic matter alterations. Nevertheless, field studies include overlapped effects and it is difficult distinguish the real origin of microbial response. In this work we have performed a laboratory experiment focus on the study of heated soil-water extract effect on bacterial growth, trying to isolate pH and soluble organic carbon alterations induced by heating soil at different temperatures. Bacterial growth was estimated by 3H-leucine incorporation technique which allows isolate bacterial activity response to an alteration. Different heated treatments were applied to unaltered forest soil samples, to simulate moderate (heating at 300 oC) or high (heating at 500 oC) intensity fire. In order to isolate possible pH changes effect, the experience was repeated adding pH buffers to bring the extract to the unaltered soil pH. Preliminary results show bacterial growth inhibition in both heated treatment compared to bacterial growth of the same bacterial suspension incubated with water. The reestablishment of pH improve the bacterial growth of samples incubated in heated soil-water extract, with a more marked effect on incubation soil-water extract from soil heated at 500 oC. These results evidence the importance of pH changes on low pH adapted bacterial community and the presence of other factors presents in the soluble fraction that are limiting bacterial proliferation

The key aspects of innovation-oriented regional industrial and economic policy

Integration processes taking place in the economy, the new requirements to enhance the effectiveness of production during international competition as well as the need to ensure the social conditions lead to the development and implementation of innovation-oriented regional industrial and economic policy, which in its turn, requires adopting substantial organizational and economic recommendations

Partial drying accelerates bacterial growth recovery to rewetting

Fluctuations in soil moisture create drying-rewetting events affecting the activity of microorganisms. Microbial responses to drying-rewetting are mostly studied in soils that are air-dried before rewetting. Upon rewetting, two patterns of bacterial growth have been observed. In the Type 1 pattern, bacterial growth rates increase immediately in a linear fashion. In the Type 2 pattern, bacterial growth rates increase exponentially after a lag period. However, soils are often only partially dried. Partial drying (higher remaining moisture content before rewetting) may be considered a less harsh treatment compared with air-drying. We hypothesized that a soil with a Type 2 response upon rewetting air-dried soil would transform into a Type 1 response if dried partially before rewetting. Two soils were dried to a gradient of different moisture content. Respiration and bacterial growth rates were then measured before and during 48 h after rewetting to 50% of water holding capacity (WHC). Initial moisture content determined growth and respiration in a sigmoidal fashion, with lowest activity in air-dried soil and maximum above ca. 30% WHC. Partial drying resulted in shorter lag periods, shorter recovery times and lower maximum bacterial growth rates after rewetting. The respiration after rewetting was lower when soil was partially dried and higher when soils were air-dried. The threshold moisture content where transition from a Type 2 to a Type 1 response occurred was about 14% WHC, while >30% WHC resulted in no rewetting effect. We combine our result with other recent reports to propose a framework of response patterns after drying-rewetting, where the harshness of drying determines the response pattern of bacteria upon rewetting dried soils

Adaptation of soil microbial communities to temperature: comparison of fungi and bacteria in a laboratory experiment

Temperature not only has direct effects on microbial activity, but can also affect activity indirectly by changing the temperature dependency of the community. This would result in communities performing better over time in response to increased temperatures. We have for the first time studied the effect of soil temperature (5–50 °C) on the community adaptation of both bacterial (leucine incorporation) and fungal growth (acetate‐in‐ergosterol incorporation). Growth at different temperatures was estimated after about a month using a short‐term assay to avoid confounding the effects of temperature on substrate availability. Before the experiment started, fungal and bacterial growth was optimal around 30 °C. Increasing soil temperature above this resulted in an increase in the optimum for bacterial growth, correlated to soil temperature, with parallel shifts in the total response curve. Below the optimum, soil temperature had only minor effects, although lower temperatures selected for communities growing better at the lowest temperature. Fungi were affected in the same way as bacteria, with large shifts in temperature tolerance at soil temperatures above that of optimum for growth. A simplified technique, only comparing growth at two contrasting temperatures, gave similar results as using a complete temperature curve, allowing for large scale measurements also in field situations with small differences in temperature

Microbial community structure of vineyard soils with different pH and copper content

The phospholipid fatty acid (PLFA) pattern of vineyard soils from the Northwest of the Iberian Peninsula was studied to identify soil factors determining the microbial community structure, with special emphasis on effects of Cu pollution and pH. A wide range of soil samples, collected from six winegrowing regions (Rías Baixas, Ribeiro, Ribeira Sacra, Monterrei, Valdeorras and Vinhos Verdes) was analyzed. Physico-chemical properties, including total Cu content, five different Cu fractions and available Cu, were also determined. Total Cu varied between 33 and 1120 mg kg1 and pHwater between 4.3 and 7.3. Soil pH rather than Cu content was most important in determining the composition of the microbial community. An increase in the relative concentrations of the monounsaturated PLFAs 16:1ω5, 16:1ω7c, 17:1ω8 and 18:1ω7 and a decrease of br18:0, i17:0, 17:0 and cy19:0 was correlated to an increase in pH. A significant effect of Cu was also found, with an increase in the branched fatty acids 10Me17:0, i16:0, 10Me18:0, a17:0 and br17:0 as consequence of Cu pollution. This change in the PLFA pattern was correlated to both the total and available fractions of Cu. Although the PLFA pattern was a useful tool to assess factors affecting the microbial composition, it is difficult to differentiate between these factors.Xunta de Galicia | Ref. 09MDS013291P

Estimation of baseline levels of bacterial community tolerance to Cr, Ni, Pb, and Zn in unpolluted soils, a background for PICT (pollution-induced community tolerance) determination

The PICT method (pollution-induced community tolerance) can be used to assess whether changes in soil microbial response are due to heavy metal toxicity or not. Microbial community tolerance baseline levels can, however, also change due to variations in soil physicochemical properties. Thirty soil samples (0–20 cm), with geochemical baseline concentrations (GBCs) of heavy metals and from five different parent materials (granite, limestone, schist, amphibolite, and serpentine), were used to estimate baseline levels of bacterial community tolerance to Cr, Ni, Pb, and Zn using the leucine incorporation method. General equations (n = 30) were determined by multiple linear regression using general soil properties and parent material as binary variables, explaining 38% of the variance in log IC50 (concentration that inhibits 50% of bacterial growth) values for Zn, with 36% for Pb, 44% for Cr, and 68% for Ni. The use of individual equations for each parent material increased the explained variance for all heavy metals, but the presence of a low number of samples (n = 6) lead to low robustness. Generally, clay content and dissolved organic C (DOC) were the main variables explaining bacterial community tolerance for the tested heavy metals. Our results suggest that these equations may permit applying the PICT method with Zn and Pb when there are no reference soils, while more data are needed before using this concept for Ni and Cr.This study has been funded by the Spanish Ministry of Economy and Competitiveness through the project CTM2015-73422-JIN (FEDER Funds). David Fernández-Calviño holds a Ramón y Cajal contract (RYC-2016–20411) fnanced by the Spanish Ministry of Economy, Industry and Competitiveness. Claudia CampilloCora holds a predoctoral fellowship fnanced by Xunta de Galicia (ED481A-2020/084). Diego Soto-Gómez was supported by a postdoctoral fellowship from the Spanish Ministry of Education “Juan de la Cierva Formación (FJC2019-039176-I).

Soil bacterial and fungal communities across a pH gradient in an arable soil

Soils collected across a long-term liming experiment (pH 4.0-8.3), in which variation in factors other than pH have been minimized, were used to investigate the direct influence of pH on the abundance and composition of the two major soil microbial taxa, fungi and bacteria. We hypothesized that bacterial communities would be more strongly influenced by pH than fungal communities. To determine the relative abundance of bacteria and fungi, we used quantitative PCR (qPCR), and to analyze the composition and diversity of the bacterial and fungal communities, we used a bar-coded pyrosequencing technique. Both the relative abundance and diversity of bacteria were positively related to pH, the latter nearly doubling between pH 4 and 8. In contrast, the relative abundance of fungi was unaffected by pH and fungal diversity was only weakly related with pH. The composition of the bacterial communities was closely defined by soil pH; there was as much variability in bacterial community composition across the 180-m distance of this liming experiment as across soils collected from a wide range of biomes in North and South America, emphasizing the dominance of pH in structuring bacterial communities. The apparent direct influence of pH on bacterial community composition is probably due to the narrow pH ranges for optimal growth of bacteria. Fungal community composition was less strongly affected by pH, which is consistent with pure culture studies, demonstrating that fungi generally exhibit wider pH ranges for optimal growth. The ISME Journal (2010) 4, 1340-1351; doi: 10.1038/ismej.2010.58; published online 6 May 2010&nbsp

The use of neutral lipid fatty acids to indicate the physiological conditions of soil fungi

The usefulness of measuring neutral lipid fatty acids (NLFAs) and phospholipid fatty acids (PLFAs) separately in order to interpret perturbation effects on soil and compost microorganisms has been studied. Initially the NLFA/PLFA ratios were studied in different soils. Low ratios were found for fatty acids common in bacteria, especially for cyclopropane fatty acids. Higher ratios were found for fatty acids common in eukaryotic organisms such as fungi (18:1(09 and 18:2omega6,9) or in saturated fatty acids, common to many types of organisms. Adding glucose to a forest soil increased the amounts of the fungal NLFAs 18:1omega9 and 18:2omega6,9 up to 60 and 10 times, respectively, after 10 days, followed by a gradual decrease. After 3 months incubation, higher levels of these NLFAs were still found compared with the control samples. Adding glucose together with nitrogen (N) and phosphorus (P) resulted in no increase in NLFAs but a 10-fold increase in the PLFAs 18:1omega9 and 18:2omega6,9. Thus, the NLFA/PLFA ratios for these fatty acids were lower than in the no-addition control when glucose was added together with N and P, but higher when glucose was added alone, even 3 months after the addition. Adding N+P without glucose did not affect the NLFA/PLFA ratio for any fatty acid. Increasing NLFA/PLFA ratios for the fungal fatty acids were also found with time after the thermophilic phase in a compost, indicating increased availability of easily available carbon

Estimation of fungal growth rates in soil using C-14-acetate incorporation into ergosterol

A technique to estimate fungal growth rates in field samples was tested in soil. The technique is based on the addition of C-14-acetate to a soil slurry and the subsequent uptake and incorporation of the labelled acetate into the fungus specific substance ergosterol by the fungi. The addition of fungal inhibitors decreased acetate incorporation rates, while bacterial inhibitors did not. Fungus-free soil exhibited no incorporation of acetate into ergosterol, indicating that the method was specific for measuring fungal activity. Incorporation rates were linear up to 18 h after the addition of acetate indicating that changing the conditions (adding acetate as a solution to a soil slurry) did not affect the incorporation rate. Problems associated with saturation of the incorporation of the added acetate were encountered, which together with uncertain conversion factors made calculations of absolute growth rates difficult. However, for relative comparisons the technique worked well. This was exemplified by measuring the relationship between temperature and growth rate of the soil fungal community, where an optimum temperature between 25 and 30 degreesC and an apparent minimum temperature for fungal growth of -11 degreesC were found. The technique was also used to indicate which nutrients limited instantaneous fungal growth in soil by adding carbon, nitrogen and phosphorus in different combinations and measuring the rate of acetate incorporation into ergosterol 2 days later. Carbon appeared to be the limiting nutrient for fungal growth in both an agricultural soil and a forest humus soil. (C) 2001 Elsevier Science Ltd. All rights reserved

Use of pollution-induced community tolerance of the bacterial community to detect phenol toxicity in soil.

Pollution-induced community tolerance (PICT) was used to study effects of phenol on soil bacteria. Phenol was added to an agricultural soil in a microcosm experiment. The effects were studied for up to four months. Bacterial growth rates were estimated with the leucine incorporation technique. This technique was also used as detection method for PICT. Changes in community structure were studied using the phospholipid fatty acid (PLFA) pattern. Increased phenol PICT of the bacterial community was found at phenol concentrations above 1 micromol/g wet weight soil. Direct inhibiting effect on bacterial growth rates 1 d after adding phenol was correlated to PICT. Phenol toxicity was reflected by changes in the structure of the bacterial community, although PICT appeared more sensitive than the PLFA method. In soil amended with 1 to 10 micromol phenol/g soil, bacterial growth recovered within one week. In the soil amended with the highest phenol concentration (30 micromol/g soil), bacterial growth rate recovered from total inhibition after 27 d, eventually reaching values six times higher than in the control. However, PICT did not change during the four months the experiment was performed. The specificity of PICT was also studied by examining cotolerance to 2-chlorophenol, 2,4-dichlorophenol, 2,3,6-trichlorophenol, Cu, and Zn. Adding phenol induced cotolerance of the bacterial community to the other phenols, although always at a lover level than to phenol. No cotolerance was found to metals in phenol-polluted soil. We conclude that the PICT concept is a valuable tool in determining phenol toxicity to bacterial communities, especially in situations where bacterial growth has recovered. Cotolerance between different phenols can, however, make interpretations of PICT more complicated