Further Insights into Metal-DOM Interaction: Consideration of Both Fluorescent and Non-Fluorescent Substances

Information on metal binding with fluorescent substances has been widely studied. By contrast, information on metal binding with non-fluorescent substances remains lacking despite the dominance of these substances in aquatic systems. In this study, the metal binding properties of both fluorescent and non-fluorescent substances were investigated by using metal titration combined with two-dimensional correlation spectroscopy (2D–COS) analysis. The organic matters in the eutrophic algae-rich lake, including natural organic matters (NOM) and algae-induced extracellular polymeric substances (EPS), both contained fluorescent and non-fluorescent substances. The peaks in the one-dimensional spectra strongly overlapped, while 2D–COS can decompose the overlapped peaks and thus enhanced the spectral resolution. Moreover, 2D FTIR COS demonstrated that the binding susceptibility of organic ligands in both NOM and algal EPS matrices followed the order: 3400>1380>1650 cm⁻¹, indicative the significant contribution of non-fluorescent ligands in metal binding. The modified Stern-Volmer equation also revealed a substantial metal binding potential for the non-fluorescent substances (logK_M: 3.57∼4.92). As for the effects of organic ligands on metal binding, EPS was characterized with higher binding ability than NOM for both fluorescent and non-fluorescent ligands. Algae-induced EPS and the non-fluorescent substances in eutrophic algae-rich lakes should not be overlooked because of their high metal binding potential.     

Microbial diversity in lake sediments detected by PCR-DGGE

In this study, PCR-denaturing gradient gel electrophoresis (DGGE) was applied to analyze the microbial communities in lake sediments from Lake Xuanwu, Lake Mochou in Nanjing and Lake Taihu in Wuxi. Sediment samples from seven locations in three lakes were collected and their genomic DNAs were extracted. The DNA yields of the sediments of Lake Xuanwu and Lake Mochou were high (10 μg/g), while that of sediments in Lake Taihu was relatively low. After DNA purification, the 16S rDNA genes (V3 to V5 region) were amplified and the amplified DNA fragments were separated by parallel DGGE. The DGGE profiles showed that there were five common bands in all the lake sediment samples indicating that there were similarities among the populations of microorganisms in all the lake sediments. The DGGE profiles of Lake Xuanwu and Lake Mochou were similar and about 20 types of microorganisms were identified in the sediment samples of both lakes. These results suggest that the sediment samples of these two city lakes (Xuanwu, Mochou) have similar microbial communities. However, the DGGE profiles of sediment samples in Lake Taihu were significantly different from these two lakes. Furthermore, the DGGE profiles of sediment samples in different locations in Lake Taihu were also different, suggesting that the microbial communities in Lake Taihu are more diversified than those in Lake Xuanwu and Lake Mochou. The differences in microbial diversity may be caused by the different environmental conditions, such as redox potential, pH, and the concentrations of organic matters. Seven major bands of 16S rDNA genes fragments from the DGGE profiles of sediment samples were further re-amplified and sequenced. The results of sequencing analysis indicate that five sequences shared 99%–100% homology with known sequences (Bacillus and Brevibacillus, uncultured bacteria), while the other two sequences shared 93%–96% homology with known sequences (Acinetobacter, and Bacillus). The study shows that the PCR-DGGE technique combined with sequence analysis is a feasible and efficient method for the determination of microbial communities in sediment samples. __________ Translated from Acta Ecologica Sinica, 2006, 26(11): 3610–3616 [译自: 生态学报]     

Cloning of a dibutyl phthalate hydrolase gene from Acinetobacter sp. strain M673 and functional analysis of its expression product in Escherichia coli

A dibutyl phthalate (DBP) transforming bacterium, strain M673, was isolated and identified as Acinetobacter sp. This strain could not grow on dialkyl phthalates, including dimethyl, diethyl, dipropyl, dibutyl, dipentyl, dihexyl, di(2-ethylhexyl), di-n-octyl, and dinonyl phthalate, but suspensions of cells could transform these compounds to phthalate via corresponding monoalkyl phthalates. During growth in Luria–Bertani medium, M673 produced the high amounts of non-DBP-induced intracellular hydrolase in the stationary phase. One DBP hydrolase gene containing an open reading frame of 1,095 bp was screened from a genomic library, and its expression product hydrolyzed various dialkyl phthalates to the corresponding monoalkyl phthalates.     

Effect of decabromodiphenyl ether (BDE 209) on soil microbial activity and bacterial community composition

In many areas of the world, polybrominated diphenyl ethers are ubiquitous due to their use as fire retardants. It is known that the hydrophobic characteristics of PBDEs cause them to sink in soil and sediment, yet their effect on microbes within the soil is not well understood. In this study, soil was treated with 1, 10, and 100 mg kg⁻¹ BDE 209 for up to 45 days. Treatment effects on soil enzymatic activities for urease and catalase were evaluated. The impact on the microbe community structure was estimated using denaturing gradient gel electrophoresis after polymerase chain reaction amplification of total genomic DNA, using bacterial variable V3 region targeted primers. The effects on the soil microbial community size and major bacterial groups were evaluated using fluorescence in situ hybridization analysis. Forty-five days after the addition of BDE 209, urease activity was suppressed by BDE 209, even at a concentration of 1 mg kg⁻¹. Catalase activity increased in the samples containing lower concentrations of BDE 209, but was suppressed in samples containing higher concentrations. The bacterial community also varied in response to the addition of BDE 209, and the variation of community composition differed among treatments. In addition, α, β and γ subclass proteobacteria decreased in the group of 100 mg kg⁻¹ BDE 209 spiked soil after 45 days of treatment. Throughout the experiment, no BDE 209 degradation was detected under darkness. These observations demonstrated that BDE 209 in soil, although of low bioavailability, had an adverse impact on the structure and function of the soil microbial community and microbial processes.     

Phosphorus cycling between the colonial cyanobacterium <Emphasis Type="Italic">Microcystis aeruginosa</Emphasis> and attached bacteria, <Emphasis Type="Italic">Pseudomonas</Emphasis>

Phosphorus (P) transfer between Microcystis aeruginosa and the attached bacterium Pseudomonas was studied using radioactive P (³²P) and green fluorescence protein-labeled Pseudomonas. M. aeruginosa in P-starved condition took up most ³²P (70%) in water and about 50% of ³²P in ³²P-saturated bacteria in individual experiments. However, only 26% of ³²P in the ³²P-saturated M. aeruginosa was transferred to P-starved bacteria. The P-starved M. aeruginosa had an advantage to take up P over the bacteria and its growth rates and abundance were higher in combined cultures, with bacteria as the biotic P source. The rate of P transfer from bacteria to the cyanobacteria was slow. P cycles predominantly between M. aeruginosa and Pseudomonas with little variation in the water. This ability is very useful for the colony-forming M. aeruginosa, especially if phosphate concentrations in water are low during water bloom periods.     

PCR-DGGE技术用于湖泊沉积物中微生物群落结构多样性研究

采用PCR-DGGE分子指纹图谱技术比较南京市玄武湖、奠愁湖和太湖不同位置的表层沉积物微生物群落结构,研究结果表明,三湖泊沉积物微生物的16SrDNA的PCR扩增结果约为626bp,为16S rDNA V3～V5区特异性片段。玄武湖和莫愁湖表层沉积物中大约有20种优势菌群,且同一湖泊不同采样点DGGE图谱的差异性不大,细菌群落结构具有较高的相似性,而太湖样品DGGE条带的数目和位置表现出明显差异,且不同采样点图谱的差异性较大。三湖泊除具有特征性的微生物种属外,还分布约5个相同的细菌种群,可能与沉积物的理化性质和水生植被的影响相关。对DGGE图谱中7条主带进行回收、扩增和测序,结果显示其优势菌群具有不同的序列组成,其中5个序列与Genebank中已登录的细菌种群的同源性≥99％,2个序列的同源性为96％和93％,其中2个相似的细菌类群目前尚未获得纯培养。     

‘圣诞快乐’朱顶红花芽分化研究

采用解剖观测和石蜡切片技术,对朱顶红品种‘圣诞快乐’花芽生长情况、花器官分化和性细胞分化过程进行了研究,以明确朱顶红花芽分化特征,为其花发育、花期调控、杂交育种和系统分类研究提供理论依据。结果表明：‘圣诞快乐’朱顶红每年产生2个花序芽,在第2年完成其内花芽花器官分化,经过低温作用后于第3年盛开,其中第2个花序偶有败育发生;花器官分化过程包括花原基分化期、外花被原基分化期、内花被原基分化期、雄蕊原基分化期、心皮原基分化期,对应的花芽大小分别约为0.02、0.05、0.1、0.2、0.3 cm,所有花器官均为螺旋状向心式发生;朱顶红花药4室,花药壁从外至内由表皮、药室内壁、中层和绒毡层组成,绒毡层类型为分泌型,小孢子减数分裂类型为连续型,四分体排列方式为十字交叉型,成熟花粉粒为2-细胞型;朱顶红雌蕊3心皮,下位子房,中轴胎座,3心室,每室两列倒生胚珠,胚珠为双珠被,厚珠心,具葱型胚囊。     

Rewiring the respiratory pathway of Lactococcus lactis to enhance extracellular electron transfer

Lactococcus lactis, a lactic acid bacterium with a typical fermentative metabolism, can also use oxygen as an extracellular electron acceptor. Here we demonstrate, for the first time, that L. lactis blocked in NAD⁺ regeneration can use the alternative electron acceptor ferricyanide to support growth. By electrochemical analysis and characterization of strains carrying mutations in the respiratory chain, we pinpoint the essential role of the NADH dehydrogenase and 2-amino-3-carboxy-1,4-naphtoquinone in extracellular electron transfer (EET) and uncover the underlying pathway systematically. Ferricyanide respiration has unexpected effects on L. lactis, e.g., we find that morphology is altered from the normal coccoid to a more rod shaped appearance, and that acid resistance is increased. Using adaptive laboratory evolution (ALE), we successfully enhance the capacity for EET. Whole-genome sequencing reveals the underlying reason for the observed enhanced EET capacity to be a late-stage blocking of menaquinone biosynthesis. The perspectives of the study are numerous, especially within food fermentation and microbiome engineering, where EET can help relieve oxidative stress, promote growth of oxygen sensitive microorganisms and play critical roles in shaping microbial communities.