Aerobic and microaerophilic bacteria isolated from Psoroptes cuniculi

The bacterial flora of Psoroptes cuniculi removed from nine naturally infested rabbits was investigated. Mites were collected in sterile glass tubes; half of the mites were surface sterilised, the others were not. All mites were crushed using sterile glass pestles, placed in Buffered Peptone Broth, smeared on to several culture media, by glass rods, and incubated at 37 degrees C for 48 hours, aerobically and/or in 5% CO2. Representative colonies were removed and streaked on to several selective media. Different colour changes of the selective media used, macro and microscopic morphology, ability to grow aerobically, Gram staining, and several biochemical tests evaluated with API test strips, were used for bacterial identification. Staphylococcus aureus, Serratia marcescens and S. odorifera were the bacteria isolated from surface sterilised mites.     

Aerobic chromate reduction by chromium-resistant bacteria isolated from serpentine soil

A group of 34 chromium-resistant bacteria were isolated from naturally occurring chromium percolated serpentine soil of Andaman (India). These isolates displayed different degrees of chromate reduction under aerobic conditions. One of the 34 isolates identified as Bacillus sphaericus was tolerant to 800 mg l⁻¹ Cr(VI) and reduced >80% Cr(VI) during growth. In Vogel Bonner broth, B. sphaericus cells (10¹⁰ cells ml⁻¹) reduced 62% of 20 mg l⁻¹ of Cr(VI) in 48 h with concomitant discoloring of yellow medium to white one. Reduction of chromate was pronounced by the addition of glucose and yeast extract as electron donors. In the presence of 4.0 g l⁻¹ of glucose, 20 mg l⁻¹ of Cr(VI) was reduced to 2.45 mg l⁻¹ after 96 h of incubation. Optimum pH and temperature for reduction were 6.0 and 25 °C, respectively. Increase in cell density and initial Cr(VI) concentration increased chromate reduction but was inhibited by metal ions like, Ni²⁺, Co²⁺, Cd²⁺ and Pb²⁺. Experiments with cell-free extracts indicated that the soluble fraction of the cell was responsible for aerobic reduction of Cr(VI) by this organism.     

Aerobic and anaerobic metabolism of squalene by a denitrifying bacterium isolated from marine sediment

The aerobic and anaerobic metabolism of the isoprenoid alkene squalene was investigated in a new type of marine denitrifying bacterium, strain 2sq31, isolated from marine sediment. Strain 2sq31 was identified as a species of Marinobacter. Under denitrifying conditions, the strain efficiently degraded squalene; of 0.7 mmol added per liter of medium, 77% was degraded within 120 days under anoxic conditions with nitrate as electron acceptor. Tertiary diols and methyl ketones were identified as metabolites, and an anaerobic pathway was suggested to explain the formation of such compounds. The first step in anaerobic degradation of squalene by strain 2sq31 involves hydration of double bonds to tertiary alcohols. Under oxic conditions, the degradation of squalene by strain 2sq31 was rapid and involved oxidative splitting of the C-10/C-11 or C-14/C-15 double bonds, in addition to the pathways observed under denitrifying conditions.     

Aerobic reduction of perchlorate by bacteria isolated in Kerala, South India

Possibility of perchlorate reduction by microbes raises hope for an eco-friendly mode of degradation of this toxic rocket fuel. This study reports 3 isolates (A1, A2 and A3) capable of molybdenum-independent degradation of perchlorate under aerobic conditions. The rate of degradation was the highest when perchlorate concentration was 17 mM, and then 3.2 mM, 4.7 mM and 4.1 mM of perchlorate was reduced by isolates A1, A2 and A3 (respectively) after 72 h at 28°C under aerobic conditions. Presence of perchlorate at a concentration higher than 17 mM resulted in some inhibition of perchlorate reduction. 16S ribosomal RNA gene analysis revealed isolate A1 to bePseudomonas stutzeri (Proteobacteria) while isolates A2 ad A3 where found to belong to the genusArthrobacter (Actinobacteria). The study, apart from demonstrating ribotyping as a rapid method of identification of economically important soil microbes, also raised prospects for using artificial consortia for environmental degradation of perchlorate, without apparent domination ofDechloromonas spp. (a group of microbes known for perchlorate remediation in the environment).     

Rate of isolated hemicellulose degradation and utilization by pure cultures of rumen bacteria

Rate studies on the utilization or degradation (or both) of isolated hemicelluloses were conducted with six strains of rumen cellulolytic bacteria. Utilization was estimated by total pentose loss, and degradation values were based on solubilization of the hemicellulose in acidified 80% ethyl alcohol. With the various strains of ruminococci, degradation of flax and fescue grass hemicellulose was near the maximum within the first 12 hr of incubation. However, where applicable, the rates of utilization were considerably slower. Both degradation and utilization of corn hull hemicellulose occurred at much slower rates than observed with the other two substrates. With flax and fescue grass hemicellulose, the rates of degradation did not appear to be influenced by the organism's ability, or inability, to utilize the substrate as an energy source. The rates and extent of isolated hemicellulose degradation and utilization were compared between the cellulolytic ruminococci and three strains of bacteria isolated from the rumen with a xylan medium. Similar values were obtained with both types of bacteria. These observations would suggest that the cellulolytic ruminococci may be important in the overall fermentation of forage hemicelluloses in the rumen. The acidified 80% ethyl alcohol supernatant fluids, obtained from fermentations of isolated fescue grass hemicellulose by two strains of Ruminococcus flavefaciens, of which only one was able eventually to utilize the substrate, were investigated by thin-layer chromatography. Results indicated that soluble oligosaccharides were produced, which were observed to disappear gradually with time in fermentations with the utilizing strain and to accumulate in fermentations with the nonutilizing strain. Examination of the acidified 80% ethyl alcohol-insoluble residue hydrolysates, obtained from fermentations with the utilizing strain, revealed that the concentration of all the constituent sugars decreased uniformly.     

Aerobic uranium (VI) bioprecipitation by metal-resistant bacteria isolated from radionuclide- and metal-contaminated subsurface soils

In this study, the immobilization of toxic uranium [U(VI)] mediated by the intrinsic phosphatase activities of naturally occurring bacteria isolated from contaminated subsurface soils was examined. The phosphatase phenotypes of strains belonging to the genera, Arthrobacter, Bacillus and Rahnella, previously isolated from subsurface soils at the US Department of Energy's (DOE) Oak Ridge Field Research Center (ORFRC), were determined. The ORFRC represents a unique, extreme environment consisting of highly acidic soils with co-occurring heavy metals, radionuclides and high nitrate concentrations. Isolates exhibiting phosphatase-positive phenotypes indicative of constitutive phosphatase activity were subsequently tested in U(VI) bioprecipitation assays. When aerobically grown in synthetic groundwater (pH 5.5) amended with 10 mM glycerol-3-phosphate (G3P), phosphatase-positive Bacillus and Rahnella spp. strains Y9-2 and Y9602 liberated sufficient phosphate to precipitate 73% and 95% of total soluble U added as 200 microM uranyl acetate respectively. In contrast, an Arthrobacter sp. X34 exhibiting a phosphatase-negative phenotype did not liberate phosphate from G3P or promote U(VI) precipitation. This study provides the first evidence of U(VI) precipitation via the phosphatase activity of naturally occurring Bacillus and Rahnella spp. isolated from the acidic subsurface at the DOE ORFRC.     

Aerobic biodegradation of nonylphenol by cold-adapted bacteria

Three strains capable of mineralizing nonylphenol as sole carbon source were isolated from a sample of contaminated soil and characterized as two Pseudomonas spp. and a Stenotrophomonas sp. The two Pseudomonas spp. expressed characteristics typical of psychrophiles growing optimally of 10 °C and capable of growing at 0 °C. The Stenotrophomonas sp. was more likely psychrotrophic because it had an optimal temperature between 14 and 22 °C although it was not capable of growing at 4 °C. At 14 °C, one of the Pseudomonas spp. exhibited the highest rate of degradation of nonylphenol (4.4 mg l^–1 d^–1), when compared with axenic or mixed cultures of the isolates. This study represents, to the best of our knowledge, the first reported case of cold-adapted microorganisms capable of mineralizing nonylphenol.     

Effect of oxygen on acetylene reduction by photosynthetic bacteria

The effect of dissolved oxygen concentration on nitrogenase activity was studied in three species of photosynthetic bacteria. The O2 concentration in the cell suspension was measured with an O2 electrode inserted into the reaction vessel. Acetylene reduction by whole cells of Rhodopseudomonas capsulata, Rhodospirillum rubrum, and Chromatium vinosum strain D was inhibited 50% by 0.73, 0.32, and 0.26 microM O2, respectively. The inhibition of the activity by O2 in R. capsulata usually was reversed completely by reestablishing anaerobic conditions. In R. rubrum and C. vinosum the inhibition was only partially reversible. The respiration rate of R. capsulata was the highest of the three, that of R. rubrum was intermediate, and that of C. vinosum was lowest. R. capsulata and R. rubrum cells were broken after their acetylene reduction activity in vivo had been completely inhibited by O2, and nitrogenase was found to be active in vitro. A concentration of cyanide that did not affect acetylene reduction activity, but which inhibited 75 to 90% of the O2 uptake by whole cells of R. capsulata, shifted the O2 concentration causing 50% inhibition of nitrogenase activity from 0.73 microM to 2.03 microM. These results are in accordance with the assumption that within a limited range of O2 concentrations, the respiratory activity of the cells is enough to scavenge the O2 and to keep the interior of the cells essentially anaerobic. It is suggested that O2 inhibits nitrogenase activity by competing for a limited supply of electrons. When cyanide is present, respiration is slower but is adequate to keep the nitrogenase environment in the cell anaerobic. The lower respiration rate may allow a greater proportion of the electrons to be used for acetylene reduction.     

Aerobic biodegradation of propylene glycol by soil bacteria

Propylene glycol (PG) is a main component of aircraft deicing fluids and its extensive use in Northern airports is a source of soil and groundwater contamination. Bacterial consortia able to grow on PG as sole carbon and energy source were selected from soil samples taken along the runways of Oslo Airport Gardermoen site (Norway). DGGE analysis of enrichment cultures showed that PG-degrading populations were mainly composed by Pseudomonas species, although Bacteroidetes were found, as well. Nineteen bacterial strains, able to grow on PG as sole carbon and energy source, were isolated and identified as different Pseudomonas species. Maximum specific growth rate of mixed cultures in the absence of nutrient limitation was 0.014 h^?1 at 4 °C. Substrate C:N:P molar ratios calculated on the basis of measured growth yields are in good agreement with the suggested values for biostimulation reported in literature. Therefore, the addition of nutrients is suggested as a suitable technique to sustain PG aerobic degradation at the maximum rate by autochthonous microorganisms of unsaturated soil profile.     

Phosphate uptake and utilization by bacteria and algae

Bacterial uptake of inorganic phosphate (closely investigated in Escherichia coli) is maintained by two different uptake systems. One (Pst system) is P_i-repressible and used in situations of phosphorus deficiency. The other system (Pit system) is constitutive. The Pit system also takes part in the phosphate exchange process where orthophosphate is continuously exchanged between the cell and the surrounding medium.Algal uptake mechanisms are less known. The uptake capacity increases during starvation but no clearly defined transport systems have been described. Uptake capacity seems to be regulated by internal phosphorus pools, e.g., polyphosphates. In mixed algal and bacterial populations, bacteria generally seem to be more efficient in utilizing low phosphate concentrations. The second half of this paper discusses how bacteria and algae can share limiting amounts of phosphate provided that the bacteria have pronouncedly higher affinity for phosphate. Part of the solution to this problem may be that bacteria are energy-limited rather than phosphate-limited and dependent on algal organic exudates for their energy supply.The possible phosphate exchange mechanism so convincingly demonstrated in Escherichia coli is here suggested to play a key role for the flux of phosphorus between bacteria and algae. Such a mechanism can also be used to explain the rapid phosphate exchange between the particulate and the dissolved phase which always occurs in short-term ³²P-uptake experiments in lake waters.     

Accelerated decolorization of reactive azo dyes under saline conditions by bacteria isolated from Arabian seawater sediment

Presence of huge amount of salts in the wastewater of textile dyeing industry is one of the major limiting factors in the development of an effective biotreatment system for the removal of azo dyes from textile effluents. Bacterial spp. capable of thriving under high salt conditions could be employed for the treatment of saline dye-contaminated textile wastewaters. The present study was aimed at isolating the most efficient bacterial strains capable of decolorizing azo dyes under high saline conditions. Fifty-eight bacterial strains were isolated from seawater, seawater sediment, and saline soil, using mineral salt medium enriched with 100?mg?l^?1 Reactive Black-5 azo dye and 50?g NaCl l^?1 salt concentration. Bacterial strains KS23 (Psychrobacter alimentarius) and KS26 (Staphylococcus equorum) isolated from seawater sediment were able to decolorize three reactive dyes including Reactive Black 5, Reactive Golden Ovifix, and Reactive Blue BRS very efficiently in liquid medium over a wide range of salt concentration (0–100?g NaCl l^?1). Time required for complete decolorization of 100?mg dye l^?1 varied with the type of dye and salt concentration. In general, there was an inverse linear relationship between the velocity of the decolorization reaction (V) and salt concentration. This study suggested that bacteria isolated from saline conditions such as seawater sediment could be used in designing a bioreactor for the treatment of textile effluent containing high concentration of salts.     

High genetic and physiological diversity of sulfate-reducing bacteria isolated from an oligotrophic lake sediment

The community structure of sulfate-reducing bacteria in littoral and profundal sediments of the oligotrophic Lake Stechlin (Germany) was investigated. A collection of 32 strains was isolated from the highest positive dilutions of most-probable-number series, and their partial 16S rRNA gene sequences and genomic fingerprints based on ERIC (enterobacterial repetitive intergenic consensus)-PCR were analyzed. The strains fell into eight distinct phylogenetic lineages, and the majority (70%) showed a close affiliation to the genus Desulfovibrio. Most of the remaining strains (22%) were related to the gram-positive Sporomusa and Desulfotomaculum groups. A high redundancy of 16S rRNA gene sequences was found within several of the phylogenetic lineages. This low phylogenetic diversity was most pronounced for the subset of strains isolated from oxic sediment layers. ERIC-PCR revealed that most of the strains with identical 16S rRNA gene sequences were genetically different. Since strains with identical 16S rRNA gene sequences but different genomic fingerprints also differed considerably with respect to their physiological capabilities, the high diversity detected in the present work is very likely of ecological relevance. Our results indicate that a high diversity of sulfate-reducing bacterial strains can be recovered from the natural environment using the established cultivation media. Received: 20 April 1998 / Accepted: 12 June 1998     

Aerobic biodegradation of 1,2-dichloroethane and 1,3-dichloropropene by bacteria isolated from a pulp mill wastewater effluent in South Africa

Large volumes of chlorinated aliphatic hydrocarbons are produced annually for a variety of industrial and commercial uses. They therefore constitute common contaminants of soil and groundwater causing serious environmental and human health problems. In this study, three bacteria were isolated from a pulp mill wastewater effluent in South Africa by culture enrichment technique and characterized for their ability to degrade 1,2-dichloroethane (1,2-DCE) and 1,3-dichloropropene (1,3-DCP). Specific growth rate constants of the organisms ranged between 0.864∼1.094 and 0.530∼0.585 d⁻¹ in 1.2-DCE and 1,3-DCP, respectively, while the degradation rate constant of the compounds ranged variously between 0.33 and 1.006 d⁻¹, with 1,2-DCE generally better utilized than 1,3-DCP. Gas chromatographic analysis revealed up to 75 and 80% removal of 1,2-DCE and 1,3-DCP, respectively, above that observed in the control bottles. These organisms also demonstrated high haloalkane dehalogenase activities with specific dehalogenase activities ranging between 0.25∼0.31 U (mg protein)⁻¹. Analysis of their 16S rRNA gene sequences revealed that they belong to the generaPaenibacillus, Bacillus, andMicrobacterium.     

A comparison of plasmid distribution in sediment bacteria isolated from clean and naphthalene polluted sites

Bacteria were isolated from the sediment collected from one site above and one below the naphthalene-polluted discharge from a coking plant. Fifteen per cent of the isolates obtained from the effluent discharge site contained plasmids compared with 9·4% from the clean site. There was no significant difference in plasmid distribution, in the number or size distribution of plasmids per cell. The possible ecological significance of these results is discussed.     

The utilization of organosulphonates by soil and freshwater bacteria

Utilization of the biogenic aliphatic organosulphonates taurine, isethionate, sulphoacetaldehyde and sulphoacetate was investigated in 100 soil and freshwater bacteria isolated on modified complete mineral salts medium. More than 90% could use all the compounds as sole sulphur sources, and some 10% used taurine and isethionate as sole carbon and energy, or sole carbon, energy and sulphur sources. None could mineralize sulphoacetaldehyde or sulphoacetate; however, two isolates capable of growth on sulphoacetate as sole carbon, energy and sulphur source were obtained by enrichment culture. The results suggest that in the majority of environmental bacteria the pathways of organosulphonate biodegradation may be independently controlled by the supply of carbon and sulphur to the cell, and that a number of routes may exist for cleavage of the organosulphonate C–S bond.