Arid and semi-arid ecosystems are often characterized by vegetation patchiness and variable availability of resources. Phospholipid fatty acid (PLFA) and 16S rRNA gene fragment analyses were used to compare the bulk soil microbial community structure at patchy arid and semi-arid landscapes. Multivariate analyses of the PLFA data and the 16S rRNA gene fragments were in agreement with each other, suggesting that the differences between bulk soil microbial communities were primarily related to shrub vs intershrub patches, irrespective of climatic or site differences. This suggests that the mere presence of a living shrub is the dominant driving factor for the differential adaptation of the microbial communities. Lipid markers suggested as indicators of Gram-positive bacteria were higher in soils under the shrub canopies, while markers suggested as indicators of cyanobacteria and anaerobic bacteria were elevated in the intershrub soils. Secondary differences between soil microbial communities were associated with intershrub characteristics and to a lesser extent with the shrub species. This study provides an insight into the multifaceted nature of the factors that shape the microbial community structure in patchy desert landscapes. It further suggests that these drivers not only act in concert but also in a way that is dependent on the aridity level.

There is an increasing trend to use greywater for irrigation in households. This is partly due to the notion that greywater is of better quality than wastewater and therefore does not need extensive treatment beyond addressing public health issues. The aim of the study was to evaluate the environmental impact and health risks associated with the use of greywater for irrigation on a small private farm. Over a three-year period, each of three plots on a farm was irrigated with either freshwater, fertilized water, or greywater. Irrigation water and soil from the plots were analyzed for a wide range of chemical and microbial variables. Results suggest that greywater may be of similar quality to wastewater in several parameters such as BOD and faecal coliforms. For some other variables such as boron and surfactants, greywater may even be of worse quality than wastewater. Long-term irrigation of arid loess soil with greywater may result in accumulation of salts, surfactants and boron in the soil, causing changes in soil properties and toxicity to plants. Faecal coliforms did not survive in the soil. Treating greywater before using it for irrigation is recommended, even in places where this is not a requirement.

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We hypothesized that biodegradation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX)--a widely used explosive contaminating soil and groundwater--by Rhodococcus strain YH1 is controlled by the presence of external nitrogen sources. This strain is capable of degrading RDX while using it as sole nitrogen source under aerobic conditions. Both inorganic and organic nitrogen sources were found to have a profound impact on RDX-biodegradation activity. This effect was tested in growing and resting cells of strain YH1. Nitrate and nitrite delayed the onset of RDX degradation by strain YH1, while ammonium inhibited it almost completely. In addition, 2,4,6-trinitrotoluene (TNT) inhibited RDX degradation and growth of strain YH1. On the other hand, tetrahydrophthalamide did not influence biodegradation or growth. Growth on RDX induced the expression of a cytochrome P-450 enzyme that is suggested to be involved in the first step in the aerobic pathway of RDX degradation, as identified by SDS-PAGE analysis. Ammonium and nitrite strongly repressed cytochrome P-450 expression. Our findings suggest that effective RDX bioremediation by strain YH1 requires the design of a treatment scheme that includes initial removal of ammonium, nitrite, nitrate and TNT before RDX degradation can take place.

Aim:  To study the effects of incubation conditions on the microbial community structure and activity of a TBBPA‐debrominating enrichment culture composed of bacterial and archaeal species. Methods and Results:  The effects of the methanogen inhibitor 2‐bromoethanesulfonate (BES), of the antibiotic ampicillin, of substrate (tetrabromobisphenol A, TBBPA) omission and availability of different electron donors on microbial community structure and activity were examined under anaerobic conditions. Debromination of TBBPA was blocked in the presence of ampicillin, while long‐term incubation with BES resulted in delayed debromination activity. The results suggest that the bacterial species responsible for the debromination of TBBPA, while archaeal species involved in electron donor metabolism. The enrichment culture lost its debromination activity after cultivation for 9 months without TBBPA, concomitantly with the disappearance of two DNA bands in a denaturing gradient gel electrophoresis (DGGE) analysis of 16S rRNA gene fragments corresponding to Pelobacter carbinolicus and Sphaerochaeta sp. TQ1 that were present in the original culture. When butyrate was used as an electron donor, TBBPA debromination activity was attenuated. When acetate was used as the electron donor, no debromination was observed and in addition, there was a decrease in the abundance of the mcrA gene. Conclusions:  The results indicate that to maintain a high rate of TBBPA debromination activity, it is essential to preserve the microbial community structure (bacterial and archaeal members) of this culture and supply an electron donor that produces high amounts of hydrogen when fermented. Significance and Impact of the Study:  The study provides important information for the management of cultures to be used in bioremediation of TBBPA contaminated sites.