Desert Soil Samples Research Articles

Diverse, yet-to-be-cultured members of the Rubrobacter subdivision of the Actinobacteria are widespread in Australian arid soils.

Phylogenetic analyses of ribosomal RNA gene sequences (rDNAs) retrieved from an Australian desert soil sample (Sturt National Park) revealed the presence of a number of clones which branched deeply from the high GC Gram-positive division line of descent. The most abundant group of these clones were related to Rubrobacter. An oligonucleotide probe was designed to have broad specificity to Rubrobacter and relatives. This probe was used to interrogate eight rDNA libraries representing four distinct land forms within the Australian arid zone. Relative abundance of Rubrobacter-relatives in these samples ranged from 2.6 to 10.2%. Clones from these libraries were selected for sequence analysis on the basis of a heteroduplex mobility assay to maximise the diversity represented in the sample. Phylogenetic analyses of these rDNA clones and Rubrobacter-related clones reported in the literature show strong support for three distinct groups. Database-searching revealed 'Rubrobacteria' were relatively abundant in a number of published soil rDNA libraries but absent from others. A PCR assay for group-1 'Rubrobacteria' was used to test for their presence in 21 environmental samples. Only marine and arid-zone soil samples gave positive PCR results. Taken together these results indicate 'Rubrobacteria' are a widespread group of variable abundance and diversity.

Diverse, yet-to-be-cultured members of the Rubrobacter subdivision of the Actinobacteria are widespread in Australian arid soils

Phylogenetic analyses of ribosomal RNA gene sequences (rDNAs) retrieved from an Australian desert soil sample (Sturt National Park) revealed the presence of a number of clones which branched deeply from the high GC Gram-positive division line of descent. The most abundant group of these clones were related to Rubrobacter. An oligonucleotide probe was designed to have broad specificity to Rubrobacter and relatives. This probe was used to interrogate eight rDNA libraries representing four distinct land forms within the Australian arid zone. Relative abundance of Rubrobacter-relatives in these samples ranged from 2.6 to 10.2%. Clones from these libraries were selected for sequence analysis on the basis of a heteroduplex mobility assay to maximise the diversity represented in the sample. Phylogenetic analyses of these rDNA clones and Rubrobacter-related clones reported in the literature show strong support for three distinct groups. Database-searching revealed ‘Rubrobacteria’ were relatively abundant in a number of published soil rDNA libraries but absent from others. A PCR assay for group-1 ‘Rubrobacteria’ was used to test for their presence in 21 environmental samples. Only marine and arid-zone soil samples gave positive PCR results. Taken together these results indicate ‘Rubrobacteria’ are a widespread group of variable abundance and diversity.

Soil carbon content along a rainfall gradient and inhibition of germination: a potential mechanism for regulating distribution of Plantago coronopus

The distribution of plant species in desert landscapes may be affected by inhibition of seed germination by factors in the soil. We tested the inhibition of Plantago coronopus seed germination on cyanobacterial soil crusts under laboratory conditions. Samples were collected from 10 locations along a rainfall gradient in the Negev Desert, Israel and soil crust and soil samples were collected from porcupine diggings in one location. We hypothesized that germination inhibition varies along this gradient as well as at a particular location mainly due to soil carbon content. We tested the hypothesis that soil carbon content has the same inhibition effect at both local and regional scales. There were strong negative relationships between germination and soil carbon content suggesting that this variable is at least a strong predictor of germination success for P. coronopus in Negev landscapes. Germination inhibition and its control by soil carbon content, may be an important influence on the distribution and dominance of plant species in this region.

Method for purification of bacterial endospores from soils: UV resistance of natural Sonoran desert soil populations of Bacillus spp. with reference to B. subtilis strain 168

Endospores of Bacillus spp. were purified from three Sonoran desert soil samples by Chelex extraction and NaBr density gradient centrifugation and their UV resistances compared with that of B. subtilis strain 168. Natural spore populations exhibited tight adherence to soil particles which was not readily overcome by the extraction and purification procedure. It was observed that spores purified from soil exhibited 2–3 fold higher resistance to UV (as measured by the 90% lethal dose, LD 90) than did B. subtilis strain 168 grown on NSM, a standard laboratory sporulation medium, and purified by the same extraction procedure. Cultivation of spore-forming bacteria isolated from soil on NSM resulted in production of spores with essentially identical UV resistance as strain 168, suggesting that spore UV resistance is influenced by the environment in which spores are produced.

Assessing the microped size distributions of desert soils erodible by wind

ABSTRACTThe microped size distribution of erodible soils is one of the main factors controlling the emissions of mineral aerosol. To date, the microped size distributions of desert soils in natural field conditions are not well known and thus the existing dust source models cannot be applied to natural sites. Based on dry sieving and elemental analysis of 26 soil samples collected in arid and semiarid regions, it is shown that the microped size distributions of these desert soil samples involve a combination of four major mass size populations. These four size populations correspond to salty soils, fine quartz sand, coarse dune sand and aluminosilicate silt. We show that the microped size distributions of the various desert soils, according to their mineralogical characteristics, can be calculated by a mixture involving two or three of these four populations. The main field of application for this scheme is the characterization of the erodible soil size distributions for modelling the atmospheric dust cycle.

Nonequilibrium Processes Affecting Forced Ventilation of Benzene and Xylene in a Desert Soil

A series of 23 unsaturated bench scale column experiments was carried out to study grain scale processes controlling the efficiency of soil vapor extraction for removal of volatile organic compounds (VOCs) from a desert soil sample (mass fraction of organic carbon, approximately 0.001). Experiments consisted of passing VOC‐containing, humidified (>95% relative humidity) air through an unsaturated soil column until breakthrough occurred and then passing VOC‐free air through the column until the VOC removal was complete. Effluent VOC concentrations were measured at frequent intervals. Experimental variables included VOC (benzene and p‐xylene), soil moisture content (0 to 18% by volume), concentration of VOC in the inlet air stream, and interstitial velocity (0.2 to 0.6 cm s−1). Experimental breakthrough curves were modeled with an advection‐dispersion model coupled with a first‐order rate equation to describe mass transfer between phases. At 18% moisture, slow water‐to‐air mass transfer of benzene as the rate‐limiting process explains the initial removal of benzene (C/C0 > 0.1), but the desorption profiles strongly suggest that a slower process (intraparticle pore diffusion) becomes the dominant process at longer times. The breakthrough curves for p‐xylene at 10 and 18% moisture also suggest that two sequential processes control removal of p‐xylene. The time constant for the faster process is comparable to that determined for the initial rate‐ imiting process for benzene at 18% moisture. The rate for the second process is the same order of magnitude for p‐xylene at 10 and 18% and benzene at 18%. Calculations of the mass distributions of the VOCs among air, water, and soil strongly suggest that the more hydrophobic p‐xylene tends to accumulate at the air‐water interface (up to 60% of the total mass) and that benzene primarily accumulates in the aqueous phase.

The Occurrence of Zoosporic Fungi in Desert Soils from Egypt

Summary 51 species belonging to 18 genera of zoosporic fungi were recovered from 100 desert soil samples collected from Upper Egypt. 8% of the samples were negative. Three genera were isolated in high frequency of occurrence: Allomyces, Dictyuchus and Pythium . They encountered in 90%, 77 % and 65 % of the samples. The most prevalent species were Allomyces arbuscula, Dictyuchus sterile , and Pythium debaryanum . The occurrence of zoosporic fungi is probably affected by the water content and the amount of organic matter in the samples tested.

Biological studies of martian soil analogues

Results of the study of the influence of Martian soil analogues, both as described by American scientists and as prepared by us, and of hydrogen peroxide on the viability of microorganisms are presented. The experiments were carried out using mixtures of soil analogues with desert soil and black earth (chernozem) samples, and pure cultures of microorganism. Microorganisms capable of withstanding a concentration of hydrogen peroxide in the medium as high as 1.5–2.0% were isolated. None of the 40 strains of microorganisms studied, all belonging to different systematic and physiological groups, exhibited growth inhibition on solid media in the presence of Martian soil analogues. In view of the fact that Martian soil cannot contain microorganisms in great quantities, we suggest using electroadsorption for their concentration, to make detection reliable. A device was designed for this purpose, using the principle of electroadsorption on a polarisable carrier (sterile cotton wool or cheesecloth). The concentrated suspension of microorganisms thus obtained was then characterized by various physicochemical methods.