A rapid water toxicity screening test based on oxygen uptake ofpseudomonas putida

Comparing the effect of zinc oxide and titanium dioxide nanoparticles on the ability of moderately halophilic bacteria to treat wastewater

This study evaluates the ability of moderately halophilic bacterial isolates (Serratia sp., Bacillus sp., Morganella sp., Citrobacter freundii and Lysinibacillus sp.) to treat polluted wastewater in the presence of nZnO and nTiO₂ nanoparticles. In this study, bacteria isolates were able to take up nZnO and nTiO₂ at concentrations ranging from 1 to 50 mg/L in the presence of higher DO uptake at up to 100% and 99%, respectively, while higher concentrations triggered a significant decrease. Individual halophilic bacteria exhibited a low COD removal efficiency in the presence of both metal oxide nanoparticles concentration ranged between 1 and 10 mg/L. At higher concentrations, they triggered COD release of up to − 60% concentration. Lastly, the test isolates also demonstrated significant nutrient removal efficiency in the following ranges: 23–65% for NO₃⁻ and 28–78% for PO₄³⁻. This study suggests that moderately halophilic bacteria are good candidates for the bioremediation of highly polluted wastewater containing low metal oxide nanoparticles.

Effect of three kinds of natural preservative cocktails on vacuum-packed chilled pork

The aim of this study was to investigate the effects of three different natural preservatives on the microbial profile, the total volatile base nitrogen (TVB-N), and biogenic amine contents of vacuum-packed chilled pork during storage at 4°C. Solution A comprised of tea polyphenols, chitosan, spice extract, propolis, and nisin. Solution B comprised of clove extract, cassia bark extract, ginger juice, garlic juice, and lactobacillus fermentation solution. Solution C consisted of only lactobacillus fermentation solution. The results indicated that solution A was a good natural preservative with higher bacteria inhibitory effect and higher sensory score than B and C. Besides the effect on appealing color, solution B could inhibit microbial activity although its inhibition effect was not as good as solution A. Thus, solution A could be used as a good preservative in industry. Solution C could inhibit the initial growth of Pseudomonas and partially inhibited the growth of Enterobacteriaceae; however, the content of putrescine in the pork treated with solution C was as high as 30.14 ± 2.89 mg/kg after 21 days of storage at 4°C. Hence, solution C is not an ideal preservative for vacuum-packed chilled pork.

Assessing the resistance and bioremediation ability of selected bacterial and protozoan species to heavy metals in metal-rich industrial wastewater

BACKGROUND

Heavy-metals exert considerable stress on the environment worldwide. This study assessed the resistance to and bioremediation of heavy-metals by selected protozoan and bacterial species in highly polluted industrial-wastewater. Specific variables (i.e. chemical oxygen demand, pH, dissolved oxygen) and the growth/die-off-rates of test organisms were measured using standard methods. Heavy-metal removals were determined in biomass and supernatant by the Inductively Couple Plasma Optical Emission Spectrometer. A parallel experiment was performed with dead microbial cells to assess the biosorption ability of test isolates.

RESULTS

The results revealed that the industrial-wastewater samples were highly polluted with heavy-metal concentrations exceeding by far the maximum limits (in mg/l) of 0.05-Co, 0.2-Ni, 0.1-Mn, 0.1-V, 0.01-Pb, 0.01-Cu, 0.1-Zn and 0.005-Cd, prescribed by the UN-FAO. Industrial-wastewater had no major effects on Pseudomonas putida, Bacillus licheniformis and Peranema sp. (growth rates up to 1.81, 1.45 and 1.43 d-1, respectively) compared to other test isolates. This was also revealed with significant COD increases (p < 0.05) in culture media inoculated with living bacterial isolates (over 100%) compared to protozoan isolates (up to 24% increase). Living Pseudomonas putida demonstrated the highest removal rates of heavy metals (Co-71%, Ni-51%, Mn-45%, V-83%, Pb-96%, Ti-100% and Cu-49%) followed by Bacillus licheniformis (Al-23% and Zn-53%) and Peranema sp. (Cd-42%). None of the dead cells were able to remove more than 25% of the heavy metals. Bacterial isolates contained the genes copC, chrB, cnrA3 and nccA encoding the resistance to Cu, Cr, Co-Ni and Cd-Ni-Co, respectively. Protozoan isolates contained only the genes encoding Cu and Cr resistance (copC and chrB genes). Peranema sp. was the only protozoan isolate which had an additional resistant gene cnrA3 encoding Co-Ni resistance.

CONCLUSION

Significant differences (p < 0.05) observed between dead and living microbial cells for metal-removal and the presence of certain metal-resistant genes indicated that the selected microbial isolates used both passive (biosorptive) and active (bioaccumulation) mechanisms to remove heavy metals from industrial wastewater. This study advocates the use of Peranema sp. as a potential candidate for the bioremediation of heavy-metals in wastewater treatment, in addition to Pseudomonas putida and Bacillus licheniformis.

Comparing the tolerance limits of selected bacterial and protozoan species to nickel in wastewater systems

Heavy-metal resistant microorganisms play a significant role in the treatment of industrial wastewater. The detoxifying ability of these resistant microorganisms can be manipulated for bioremediation of heavy metals in wastewater systems. This study aimed at comparing the tolerance limit of selected wastewater protozoan species (Aspidisca sp., Trachelophyllum sp. and Peranema sp.) against Ni(2+) with that of selected bacterial species (Bacillus licheniformis-ATCC12759, Brevibacillus laterosporus-ATCC64 and Pseudomonas putida-ATCC31483) commonly found in wastewater systems. The isolates were exposed to various concentrations of Ni(2+) in mixed liquor and their tolerance to Ni(2+) assessed at different temperatures (25°C, 30°C, 35°C and 40°C) and pHs (4, 6, 7, 8 and 10). The physicochemical parameters such as chemical oxygen demand (COD) and dissolved oxygen (DO) of the media and the growth rates of the isolates were measured using standard methods. In terms of their minimum inhibitory concentrations (MIC), the results revealed that the isolates could tolerate Ni(2+) at concentrations ranging between 32 and 52ppm for protozoa and between 52 and 84ppm for bacteria. B. licheniformis-ATCC12759 was the most tolerant bacterial species (MIC: 84ppm-Ni(2+)) while Peranema sp. was the most tolerant protozoan species (MIC: 52ppm-Ni(2+)). At 10 and/or 20ppm-Ni(2+) the growth of B. licheniformis-ATCC12759 (6.30 days(-1) for 10 and 5.73 days(-1) for 20ppm-Ni(2+)), P. putida-ATCC31483 (6.02 days(-1) for 10 and 5.31 days(-1) for 20ppm-Ni(2+)) and Peranema sp. (2.15 days(-1) for 10ppm-Ni(2+)) was stimulated after one day of incubation. Statistical evidence showed significant differences (p=0.0065) between the MIC of the six isolates and positive correlations between COD and the growth rates of isolates (r=0.8999/0.8810 for bacteria/protozoa). The tolerance limit of all isolates was significantly dependent on the pH and the temperature. The study suggests that these isolates can be used for the bioremediation of nickel in industrial wastewater systems.

Toxicity screening of metals with special reference to quantitative approach

A series of metals Cr(6+), Al(3+), Cd(2+), Pb(2+), Cu(2+), Zn(2+), and Hg(2+) were tested in three systems--Microtox, Motility Test, and Growth Zone Inhibition Test. Toxicity endpoint of each metal was variable from system to system. Of the three systems, Microtox was the most sensitive system. In this system, Hg(2+) reacted as the most toxic element having EC(50) value 0.08 mg/L while Cd(2+) and Cr(6+) were least toxic with their EC(50) values 19.4 and 21.0 mg/L respectively. MEC(90) value of Motility Test was always needed more concentrations of toxicant in comparison to other systems. In comparison to Microtox, ten times more concentration of Hg(2+) (1.4 mg/L) was required to find out its MEC(90) value. Growth Zone Inhibition Test was very simple method from handling point of view. The usual practice of evaluation of toxicity screening in this system is either qualitatively or semi-qualitatively. Hence a study was designed to establish a quantitative technique, Growth Inhibition Test, as an alternative to this test using the same sensor organism B. cereus, which allows determination of MAC as well as MIC. MIC for Hg(2+) was found to be 0.03 mg/L in Growth Inhibition Test while the same element was needed more concentration (1.0 mg/L) in the case of Growth Zone Inhibition test to produce halo. However, all these systems including Growth Inhibition Test showed Hg(2+) was the most toxic element.

Assessment of lead toxicity to the marine bacterium, Vibrio fischeri, and to a heterogeneous population of microorganisms derived from the Pearl River in Jackson, Mississippi, USA

Microorganisms are known to be excellent test organisms because of the relative ease for handling and suitability for analysis related to their small size, large number and convenient growing conditions. In this research, we tested the toxic effects of lead against a marine bacterium (Vibrio fischeri), and a heterogeneous population of bacteria derived from the Pearl River in Jackson, Mississippi. Using the level of bioluminescence in the Microtox Assay (V. fischeri), and the kinetics of dissolved oxygen uptake and growth (mixed bacterial population) as measures of toxicity, lead concentrations effecting a 50% reduction in these parameters (EC50) were determined as the toxic end-points. The activity quotients were also computed to determine the degrees of toxicity. Optical density (measure of growth) and oxygen uptake were measured over an extended period of time (20 h). EC50 values of 0.34 +/- 0.03, 3.10 +/- 0.01, and 3.80 +/- 0.02 mg/L were recorded for bioluminescence, growth, and oxygen uptake, respectively. As expected, the results indicated that the sensitivity to lead toxicity of V. fischeri was about one order of magnitude (10 times) greater than that of the mixed population of Pearl River microorganisms. Reductions in bioluminescence, growth, and oxygen uptake were directly correlated to lead concentrations, with toxic levels ranging from slightly toxic in lower concentrations to extremely toxic in higher concentrations. Upon 20 h of exposure, the times required to produce 50% reduction in dissolved oxygen uptake were (TD50S) 8.01 +/- 0.44, 9.60 +/- 0.46, 11.29 +/- 0.46, 13.03 +/- 0.57, 17.32 +/- 0.95, and 20.00 +/- 0.00 h in 0, 1, 2, 3, 4, 5, and 6 mg/L of lead, respectively, indicating a time-response relationship with respect to lead toxicity.

Treatability, toxicity and biodegradability test methods

1. This review confirms that treatability and biodegradability test methods have been cited extensively in the literature. It is clear that the method selected depends on the specific objectives of the test, i.e. the determination of whether a substance is toxic, biodegradable or treatable. Factors that have to be considered when selecting the test methods are the cost of performing the test, the time and resources involved, and the accuracy required. It often appears that more extensive simulation studies are required after initial screening tests have been performed. 2. Many of the enzyme and bacterial growth tests which have been developed for monitoring or screening of toxicants and their persistence in water and wastewaters have been reviewed. Most of these tests are rapid, inexpensive, and reproducible. Most of the biochemical and microcalorimetric approaches, although promising, are still in their infancy as regards toxicity testing. Therefore, biological testing still appears to be most suitable for routine assessment. 3. Micro-organisms are particularly suitable for use in toxicity testing of chemicals as they are inexpensive to culture, have rapid growth rates, and usually provide reproducible results (Vaishnav & Korthals, 1990). Many bioassays have been developed to evaluate the toxicity and treatability of municipal and industrial effluents. Numerous single species tests have been recommended by several authors (Dutka et al., 1983; Beaubien et al. 1986). Such approaches are mainly based on the belief that, by selecting the most sensitive species and by using appropriate factors to allow for variability not included in the test, the highest levels of biological organization will be adequately protected. Single species tests are now quite well established, and when properly used, are easy to analyse and quantify. However, it has been pointed out (Levin, 1984) that the results obtained from single species tests cannot easily be applied to natural field conditions because the test organisms are extensively laboratory acclimated; also the test conditions provide for optimized growth and survival, a situation unlikely to be found in the field. Moreover, a fundamental problem with this approach is that it assumes that the ecosystem is a collection of single species exposed to toxicants under constant conditions (Cairns, 1982). Multi-species toxicity tests, that is the use of mixed cultures or communities of micro-organisms for a testing protocol, are found to be generally much less sensitive than single species tests (Dutka & Kwan, 1984).(ABSTRACT TRUNCATED AT 400 WORDS)