World Journal of Microbiology and Biotechnology

Tetracycline resistance has been used as the key determinant to monitor resistance genes in natural environments such as rivers, lakes or seawater. The aim of this study was evaluate the frequency of tetA, tetB, tetC, tetD and tetE genes in 52 tetracycline-resistant Enterobacteriacea isolated from river water in the North East Black Sea Region of Turkey. In 52 tetracycline-resistant strains, resistance was mediated by tetA in eight (15.3%) strains, tetB in ten (19.2%) strains and both tetA and tetB in one (1.9%) strain. No tetC, tetD or tetE-mediated resistance was detected. In conclusion, the river water may be considered as a reservoir for the antibiotic resistance genes and the people living in this area may be under risk. To our knowledge, this is the first report for molecular characterization of tetracycline resistance in Enterobacteriaceae of river water origin in Turkey.

The present study investigated biodegradation and removal of Reactive Red 198 (RR198) dye from aqueous environments using a new bacterial consortium isolated from textile wastewater sludge on laboratory scale via batch study. Two bacterial species, Enterococcus faecalis (EF) and Klebsiella variicola (KV), were identified after isolation, through biochemical assays, Polymerase chain reaction (PCR), and 16S rRNA gene sequencing. To determine their ability to biodegrade RR198 dye, physicochemical parameters, including bacterial concentration, time, pH, and temperature, were tested; the results showed that the best conditions included a bacterial concentration of 3.5 mL × 105 cells/mL and incubation time of 72 h. Under such conditions, the removal efficiency of RR198 dye at an initial concentration of 10–25 mg/L was more than 98%; however, for concentrations of 50, 75, and 100 mg/L, removal efficiency was reduced to 55.62%, 25.82%, and 15.42%, respectively (p = 0.005). The highest removal efficiency occurred at pH 8.0, reaching 99.26% after 72 h of incubation. With increasing the incubation temperature from 25 °C to 37 °C, removal efficiency increased from 71.71 to 99.26% after 72 h of incubation, and increasing the temperature from 37 to 45 °C, the removal efficiency was reduced (p ≤ 0.001). Therefore, the EF–KV bacterial consortium can be used for efficient removal of RR198 dye from textile effluent.

Deletions and the appearance of pseudogenes in pathways of carbon source utilisation and energy metabolism best explain the host-dependency and failure to culture Mycobacterium leprae axenically. From the genome sequence it is possible to predict that acetate and galactose cannot be used as carbon sources, while pyruvate can only be catabolised. Glycerol, glucose, and fatty acids could be used for glycolysis, the pentose cycle and β-oxidation which are complete. Retrospective functional genomics – interpreting work before the completion of the genome project – supports the failure of M. leprae to use acetate as well as another prediction that metabolic flux from pyruvate to acetyl-CoA would be very low. However, the loss of a second icd gene (compared with M. tuberculosis), predicted to encode isocitrate dehydrogenase, did not diminish the specific activity of the enzyme. The genes for respiratory pathways are extremely limited, being present for oxidative phosphorylation as a result of electron transport only using FADH as an electron donor. In contrast, all the major biosynthetic pathways are complete except that M. leprae is a natural methionine auxotroph: this is predicted not to be attenuating, or explain host-dependency since methionine would be present in ‘rich’ culture media.

Bioleaching of a pyrite ore containing high concentrations of cobalt (0.1%) and zinc (0.065%) was affected by small amounts of calcitic gangue (from 0.01 to 1.01%). Results from an air-lift percolator and from Erlenmeyer flask experiments show that a small percentage of calcite raises the pH and arrests the growth of the acidophilic bacterium Thiobacillus ferrooxidans. In percolator experiments, when calcite is completely removed by the continuous addition of small quantities of acid, and the pH of the liquor becomes acid, the micro-organism begins to grow and to bio-oxidize the pyrite ore. The growth of T. ferrooxidans shows different lag phase spans (from 13 to 190 days) depending on carbonate dissolution. The metals Fe, Zn and Co are released into the leaching solution together at different rates after a lag-time which depends on calcite concentrations in pyrite gangue. Metal ratios in the mineral bulk are different from those in the liquor, Zn dissolving 5 times more readily than Co. Bioleaching rates for metal removal from pyrite are higher in percolator (for Fe, from 5 to 15 mg/l/h) than in flask experiments (from 0.5 to 2 mg/l/h), but the lag phases are shorter (from 2 to 65 days). The differences between the two systems are related to calcite dissolution and gypsum precipitation.

Static or modulated magnetic fields (MF) may interact with the biological system and affect the metabolism of microorganisms, such as their photosynthetic capacity or synthesis of carbohydrates. Their effects on microorganisms, which can be classified into inhibiting, stimulating and null, may be interpreted as the result of stress that cells undergo, thus, leading to responses through the same mechanisms. Biological effects of exposure to magnetic forces depend on magnetic intensity, frequency and exposure time. Modifications in these parameters may enhance product formation. Effects differ according to the form and application of MF characteristic parameters. Magnetic treatments have the advantages of being convenient and non-toxic, having low running cost, emitting no secondary pollution, enabling wide application and being easily shielded. MF application to the cultivation of microalgae, to improve the production of finished biomolecules, is a simple, inexpensive and powerful process. However, bioeffects of MF on microalgae need to be further investigated because there have currently been very few available reports in the literature. Thus, studies which aim at optimizing parameters involved in MF application must be developed in order to obtain the best conditions for the production of molecules with high economic potential.