Towards bioremediation of toxic unresolved complex mixtures of hydrocarbons: identification of bacteria capable of rapid degradation of alkyltetralins

Background, aim and scope  Unresolved complex mixtures (UCMs) of aromatic hydrocarbons are widespread, but often overlooked, environmental contaminants. Since UCMs are generally rather resistant to bacterial degradation, bioremediation of UCM-contaminated sites by bacteria is a challenging goal. Branched chain alkyltetralins are amongst the individual classes of components of aromatic UCMs which have been identified in hydrocarbon-contaminated sediments and a number of synthetic alkyltetralins have proved toxic in laboratory studies. Thus, alkyltetralins should perhaps be amongst the targets for UCM bioremediation strategies. The slow degradation of several alkyltetralins by a microbial consortium has been reported previously; however, the bacteria involved remain unidentified and no single strain capable of alkyltetralin biodegradation has been isolated. The present project therefore aimed to enrich and identify bacterial consortia and single strains of bacteria from a naturally hydrocarbon-contaminated site (Whitley Bay, UK), which were capable of the degradation of two synthetic alkyltetralins (6-cyclohexyltetralin (CHT) and 1-(3’-methylbutyl)-7-cyclohexyltetralin (MBCHT)). Materials and methods  Bacteria were enriched from sediment collected from Whitley Bay, UK by culturing with CHT and MBCHT for a period of 4 months. Biodegradation experiments were then established and degradation of model compounds monitored by gas chromatography–mass spectrometry. Internal standards allowed the generation of quantitative data. 16S rRNA gene clone libraries were constructed from individual enrichments to allow assessment of microbial community structure. Selective media containing MBCHT were used to isolate single bacterial strains. These strains were then tested in liquid culture for their ability to degrade MBCHT. Results  The consortia obtained through enrichment culture were able to degrade 87% of CHT and 76% of MBCHT after only 46 days compared with abiotic controls. The 16S ribosomal RNA gene clone libraries of these bacteria were dominated by sequences of Rhodococcus spp. Using selective media, a strain of Rhodococcus was then isolated that was also able to biodegrade 63% of MBCHT in only 21 days. Discussion  The present report describes the isolation of a single bacterial strain able to degrade the resistant MBCHT. Although significant losses of MBCHT were observed, putative metabolites were not detectable. Rhodococcus sp. have been reported previously to be able to biodegrade a range of hydrocarbon compounds. Recommendations and perspectives  Due to their environmental persistence and toxicity, aromatic UCMs require bioremediation. The culturing and identification of such bacteria capable of rapid degradation of alkyltetralins may be an important step toward the development of bioremediation strategies for sites contaminated with toxic UCMs.     

The influence of soil characteristics on the toxicity of four chemicals to the earthworm Eisenia fetida andrei (Oligochaeta)

Summary The acute toxicity of Cd (chloride), chloroacetamide, 3,4-dichloroaniline and pentachlorophenol to the earthworm Eisenia fetida andrei was determined using the OECD (1984) artificial soil and contact testing procedures. To investigate the influence of two soil characteristics (pH and organic-matter content), the toxicity of the chemicals was also determined in two natural sandy soils. It is concluded that the filter-paper contact test cannot be recommended to predict earthworm toxicity of these chemicals in soil. Toxicity in soil was influenced by both pH and organic-matter content. Differences between LC₅₀ values in the high-organic-matter artificial soil and in an acid, low-organic-matter sandy soil were, however, not greater than a factor of 3–4. The results of this study therefore support the use of a well-defined artificial soil substrate for standardized earthworm toxicity tests.     

不同地区松突圆蚧耐寒性的研究

为探讨松突圆蚧(Hemiberlesia pitysophila)对低温的地理适应能力,2007年测定并比较了广东信宜和福建漳州、泉州和长乐4个地区冬季松突圆蚧雌成虫的过冷却点和信宜、泉州、长乐3地区各虫态的低温暴露死亡率。结果表明:4个地区松突圆蚧雌成虫的过冷却点具有显著差异(P0.05),福建长乐的平均过冷却点最低,为-15.71℃,广东信宜的平均过冷却点最高,为-13.68℃,总体呈现随纬度升高而逐渐降低的趋势。在各种低温暴露下,广东信宜松突圆蚧种群的死亡率均明显高于福建泉州和长乐种群;尤其在-10℃时,前者的死亡率达85.97%,而后二者分别仅为37.58%和56.65%。松突圆蚧各地、各虫态的低温暴露死亡率变化规律均服从改进的双变量逻辑斯谛曲线模型(P0.01),但广东信宜各虫态和种群的致死中有效伤害低温累积(SLIT50)均明显高于福建泉州和长乐。因此认为:随分布纬度上升,松突圆蚧耐寒性存在逐步增强的趋势。     

Soil ciliate bioassay for the pore water habitat a missing link between microflora and earthworm testing in soil toxicity assessment

Background, Scope and Goal. The chemical, pesticide and biocide legislation of the European Union assembles a variety of bioassays. Among the ecotoxicological tests involved, the testing strategy for the aquatic compartment builds up on three tests reflecting the main trophic levels (algae,Daphnia, fish). For the soil compartment at least one trophic level for a basic food chain is missing, namely between microflora and earthworms. Protozoa are an ideal missing link as they were shown to be the most prominent faunal contributors to nutrient cycling in soil ecosystems and as they represent the lacking first level consumers as well as the highly diverse microfauna. As protozoa inhabit the soil pore water, they can serve as direct indicators for the solved and thus bioavailable portion of xenobiotics. In order to widen the spectrum of available toxicity tests for a meaningful effect assessment for the soil compartment, a test with the soil ciliateColpoda inflata (Ciliophora, Protozoa), introduced by Pratt et al. (1997), was improved.     

盐胁迫油菜根际中含假单胞菌（Pseudomonas spp.1）的氨基环丙烷-1-羧酸 (ACC) 脱氨基酶特征研究

When exposed to biotic or abiotic stress conditions,plants produce ethylene from its immediate precursor 1-aminocyclopropane-1-carboxylate(ACC),leading to retarded root growth and senescence.Many plant growth-promoting rhizobacteria contain the enzyme ACC deaminase and this enzyme can cleave ACC to form α-ketobutyrate and ammonium,thereby lowering levels of ethylene.The aim of this study was to isolate and characterize ACC deaminase-producing bacteria from the rhizosphere of salt-stressed canola(Brassica napus L.).Out of 105 random bacterial isolates,15 were able to utilize ACC as the sole source of nitrogen.These 15 isolates were also positive for indole acetic acid(IAA) production.Phylogenetic analysis based on partial 16 S rDNA sequences showed that all isolates belonged to fluorescent Pseudomonas spp.In the canola rhizosphere investigated in this study,Pseudomonas fluorescens was the dominant ACC deaminase-producing species.Cluster analysis based on BOX-A1R-based repetitive extragenic palindromic-polymerase chain reaction(BOX-PCR) patterns suggested a high degree of genetic variability in ACC deaminase-producing P.fluorescens strains.The presence of indigenous ACC-degrading bacteria in the rhizosphere of canola grown in saline soils indicates that these bacteria may contribute to salinity tolerance.