Pseudomonas lemoignei has five poly(hydroxyalkanoic acid) (PHA) depolymerase genes: A comparative study of bacterial and eukaryotic PHA depolymerases

Four polyhydroxyalkanoate (PHA) depolymerases were purified from the culture fluid ofPseudomonas lemoignei: poly(3-hydroxybutyrate) (PHB), depolymerase A (M _r , 55,000), and PHB depolymerase B (M _r , 67,000) were specific for PHB and copolymers of 3-hydroxybutyrate (3HB) and 3-hydroxyvalerate (3HV) as substrates. The third depolymerase additionally hydrolyzed poly(3-hydroxyvalerate) (PHV) at high rates (PHV depolymerase;M _r , 54,000). The N-terminal amino acid sequences of the three purified proteins, of a fourth partially purified depolymerase (PHB depolymerase C), and of the PHB depolymerases ofComamonas sp. were determined. Four PHA depolymerase genes ofP. lemoignei (phaZ1,phaZ2,phaZ3, andphaZ4) have been cloned inEscherichia coli, and the nucleotide sequence ofphaZ1 has been determined recently (D. Jendrossek, B. Müller, and H. G. Schlegel,Eur. J. Biochem. 218, 701–710, 1993). In this study the nucleotide sequences ofphaZ2 andphaZ3 were determined.PhaZ1,phaZ2, andphaZ4 were identified to encode PHB depolymerase C, PHB depolymerase B, and PHV depolymerase, respectively.PhaZ3 coded for a novel PHB depolymerase ofP. lemoignei, named PHB depolymerase D. None of the four genes harbored the PHB depolymerase A gene, which is predicted to be encoded by a fifth depolymerase gene ofP. lemoignei (phaZ5) and which has not been cloned yet. The deduced amino acid sequences ofphaZ1–phaZ3 revealed high homologies to each other (68–72%) and medium homologies to the PHB depolymerase gene ofAlcaligenes faecalis T₁ (25–34%). Typical leader peptide amino acid sequences, lipase consensus sequences (Gly-Xaa-Ser-Xaa-Gly), and unusually high proportions of threonine near the C terminus were found in PhaZ1, PhaZ2, and PhaZ3. Considering the biochemical data of the purified proteins and the amino acid sequences, PHA depolymerases ofP. lemoignei are most probably serine hydrolases containing a catalytical triad of Asp, His, and Ser similar to that of lipases. A comparison of biochemical and genetic data of various eubacterial and one eukaryotic PHA depolymerases is provided also.Paper presented at the Bio/Environmentally Degradable Polymer Society—Second National Meeting, August 19–21, 1993, Chicago, Illinois.     

Comparative characterization of two natural humic acids in the Pearl River Basin, China and their environmental implications

Two humic acids (HAs) were isolated from contaminated river sediments present under comparative conditions in the Pearl River Basin, China. YFHA (the HA extracted at an open pyrite mining area in Yunfu) exhibited a lower absorption intensity for certain bands in the Fourier transform infrared spectra, a lower E4/E6 value (the UV absorbances at 465 nm (E4) and 665 nm (E6)), a lower apparent molecular weight, a lower polarity and a lower oxygen functionality in comparison with GZHA (the HA isolated at an urban living area in Guangzhou). All these differences indicated a higher degree of humification of YFHA than GZHA. Overall, the enrichment patterns of permanent heavy metals in the studied HAs were similar to those in corresponding sediments. In particular, YFHA exhibited high enrichment of trace element Tl, a characteristic concomitant from the mining of the pyrite minerals. The adsorption isotherms of two HAs for goethite and pyrolusite, two representative geological materials, conformed to the Langmuir equation. Based on the qualitative relationships between the Langmuir constants of the adsorption isotherms and the chemical characteristics of HAs, the main mechanism of HA adsorption on these materials was suggested to be hydrophobic interaction. This study highlighted the promising use of HA as a peculiar bio-indicator of uncommon trace metal contaminations. The HA adsorption mechanism on representative geological materials further provided a theoretical basis for the study on the unusual metal behavior in complex environmental settings.     

Plant available phosphorus in soil as predictor for the leaching potential: Insights from long-term lysimeter studies

This study aimed to demonstrate the impact of phosphorus (P) mineral fertilization on topsoil P content and P leaching. We evaluated 83 datasets from 25 years from lysimeter experiments involving different cropping systems (winter crop, summer crop and autumn tillage, harvested grass) or unfertilized fallow, four types of soil texture, and three levels of applied mineral P fertilizer. A positive monotonic and significant correlation was indicated between P in the topsoil determined by the double lactate method (P _DL) and the yearly flow-weight total (TP) concentrations in leachates with Spearman rank correlations r _s (r _s > 0.183) and probability (p) < 0.05. The present German recommended rates of P mineral fertilization are proposed insufficient to protect fresh and marine waters from undesired P pollution and eutrophication. A long-term reduction of excess soil P is urgent along with other measures to mitigate high P inputs to surface and ground waters.     

Climate change impacts in the Middle East and Northern Africa (MENA) region and their implications for vulnerable population groups

Regional Environmental Change - The Middle East and North Africa (MENA) region emerges as one of the hot spots for worsening extreme heat, drought and aridity conditions under climate change. A...     

Leaching and crop uptake of nitrogen and phosphorus from pig slurry as affected by different application rates

The influence of increasing pig slurry applications on leaching and crop uptake of N and P by cereals was evaluated in a 3-yr study of lysimeters filled with a sandy soil. The slurry was applied at N rates of 50 (S50), 100 (S100), 150 (S150), and 200 (S200) kg ha(-1) during 2 of the 3 yr. The P rates applied with slurry were: 40 (S50), 80 (S100), 120 (S150), and 160 (S200) kg ha(-1) yr(-1). Simultaneously, NH4NO3 and Ca(H2PO4)2 were applied at rates of 100 kg N ha(-1) and 50 kg P ha(-1), respectively, to additional lysimeters (F100), while others were left unfertilized (F0). During the 3-yr period, the leaching load of total N tended to increase with increasing slurry application to, on average, 139 kg ha(-1) at the highest application rate (S200). The corresponding N leaching loads (kg ha(-1)) in the other treatments were: 75 (F0), 103 (F100), 93 (S50), 120 (S100), and 128 (S150). The loads of slurry-derived N in the S100, S150, and S200 treatments were significantly larger (P < 0.05) than those of fertilizer-derived N. In contrast, P leaching tended to decrease with increasing input of slurry, and it was lower in all treatments that received P at or above 50 kg P ha(-1) yr(-1) with slurry or fertilizer than in the unfertilized treatment. The crop use efficiency of added N and P was clearly higher when NH4NO3 and Ca(H2PO4)2 were used rather than slurry (60 vs. 35% for N, 38 vs. 6-9% for P), irrespective of slurry application rate. Therefore, from both a production and water quality point of view, inorganic fertilizers seem to have environmental benefits over pig slurry when used on sandy soils.     

Bakterielle Biotestverfahren zur Bestimmung der Toxizität von Abfällen

For a risk assessment of wastes, fast and sensitive screening methods are required to detect possible toxic effects. In this study, different leachability methods (DIN 38414, part 4; EPA 1310; EPA 1320) were used to prepare aqueous leachates from different wastes; these leachates were rested in different bacterial toxicity test systems for possible toxic effects. As bacterial toxicity tests, the luminescent bacteria test and the growth inhibition test with activated sludge bacteria were used. The test systems showed a good agreement of the results from the different leaching methods, thereby indicating the reliability of the test systems used. The luminescent bacteria inhibition test showed a higher sensitivity than the growth inhibition test which is in good accordance with literature data. We conclude that both test systems are well suited to assess the toxic potential of aqueous waste leachates.     

Arsenite toxicity and uptake rate of rice (Oryza sativa L.) in vivo

Toxicity threshold of arsenite on intact rice seedlings was determined and arsenite uptake characteristics were investigated using non-toxic concentrations of arsenite.The arsenite toxicity threshold was 2.4 μM arsenite which reduced growth by 10% (EC₁₀). The two highest arsenite levels induced wilting of seedlings and reduced both, transpiration rate and net photosynthetic rate. Arsenic content in plant tissue increased up to 10.7 μM arsenite and then declined with increasing arsenite concentration in the treatment solution. The contents of Si, P, K, and of micronutrients Cu, Fe, Mn and Zn in shoot d.m. were reduced by arsenite levels ≥ 5.3 μM. In the non-toxic range, arsenite uptake rate was linearly related to arsenite concentration.High arsenite levels reduced growth without being taken up which might be due to increasing binding of arsenite to proteins at the outer side of the plasmalemma.     

Effect of humic matter on metal adsorption onto clay materials: Testing the linear additive model

Migration of contaminants with low affinity for the aqueous phase is essentially governed by interaction with mobile carriers such as humic colloids. Their impact is, however, not sufficiently described by interaction constants alone since the humic carriers themselves are subject to a solid–liquid distribution that depends on geochemical parameters.In our study, co-adsorption of the REE terbium (as an analogue of trivalent actinides) and humic acid onto three clay materials (illite, montmorillonite, Opalinus clay) was investigated as a function of pH. ¹⁶⁰Tb(III) and ¹³¹I-labelled humic acid were employed as radiotracers, allowing experiments at very low concentrations to mimic probable conditions in the far-field of a nuclear waste repository. Humate complexation of Tb was examined by anion and cation exchange techniques, also considering competitive effects of metals leached from the clay materials.The results revealed that desorption of metals from clay barriers, occurring in consequence of acidification processes, is generally counteracted in the presence of humic matter. For all clay materials under study, adsorption of Tb was found to be enhanced in neutral and acidic systems with humic acid, which is explained by additional adsorption of humic-bound Tb.A commonly used composite approach (linear additive model) was tested for suitability in reconstructing the solid–liquid distribution of Tb in ternary systems (Tb/humic acid/clay) on the basis of data determined for binary subsystems. The model can qualitatively explain the influence of humic acid as a function of pH, but it failed to reproduce our experimental data quantitatively. It appears that the elementary processes (metal adsorption, metal–humate complexation, humic acid adsorption) cannot be considered to be independent of each other. Possible reasons are discussed.