Chongling Yan

PAHs contamination and bacterial communities in mangrove surface sediments of the Jiulong River Estuary, China.

Sixteen sediment samples collected from eight transects in a mangrove swamp of the Jiulong River Estuary, Fujian, China were investigated for their content of polycyclic aromatic hydrocarbons (PAHs) and the biodegradation potential of the indigenous microorganisms. The bacterial community structures in the mangrove sediments and in enrichment cultures were also investigated. The results showed that the total PAHs concentration of mangrove sediments ranged from 280 to 1074 ng g(-1) dry weight, that the PAHs composition pattern in the mangrove sediments was dominated by high molecular weight PAH components (4-6 rings), and that Benzo[ghi]perylene and Indeno[1,2,3-cd]pyrene were the most dominant at different stations. Abundant PAH-degrading bacteria were found in all the stations, the values of phenanthrene-degrading bacteria ranged from 5.85 x 10(4) to 7.80 x 10(5) CFU g(-1) dry weight, fluoranthene-degrading bacteria ranged from 5.25 x 10(4) to 5.79 x 10(5) CFU g(-1) dry weight, pyrene-degrading bacteria ranged from 3.10 x 10(4) to 6.97 x 10(5) CFU g(-1) dry weight and the benzo(a)pyrene-degrading bacteria ranged from 5.25 x 10(4) to 7.26 x 10(5) CFU g(-1) dry weight. DGGE analysis of PCR-amplified 16S rDNA gene fragments confirmed that there was a remarkable shift in the composition of the bacterial community due to the addition of the different model PAH compound phenanthrene (three ring PAH), fluoranthene(four ring PAH), pyrene(four ring PAH) and benzo(a)pyrene(five ring PAH) during enrichment batch culture. Eleven strains were obtained with different morphology and different degradation ability. The presence of common bands for microbial species in the cultures and in the native mangrove sediment DNA indicated that these strains could be potential in situ PAH-degraders.

Kandelia obovata (S, L) Yong tolerance mechanisms to Cadmium: Subcellular distribution, chemical forms and thiol pools

In order to explore the detoxification mechanisms adopted by mangrove under cadmium (Cd) stress, we investigated the subcellular distribution and chemical forms of Cd, in addition to the change of the thiol pools in Kandelia obovata (S., L.) Yong, which were cultivated in sandy culture medium treated with sequential Cd solution. We found that Cd addition caused a proportional increase of Cd in the organs of K. obovata. The investigation of subcellular distribution verified that most of the Cd was localized in the cell wall, and the lowest was in the membrane. Results showed sodium chloride and acetic acid extractable Cd fractions were dominant. The contents of non-protein thiol compounds, Glutathione and phytochelatins in K. obovata were enhanced by the increasing strength of Cd treatment. Therefore, K. obovata can be defined as Cd tolerant plant, which base on cell wall compartmentalization, as well as protein and organic acids combination.

NMR, HPLC-ESI-MS, and MALDI-TOF MS analysis of condensed tannins from Delonix regia (Bojer ex Hook) Raf and their bioactivities

The structures of the condensed tannins isolated from leaf, fruit, and stem bark of Delonix regia (Bojer ex Hook.) Raf. have been investigated with (13)C nuclear magnetic resonance ((13)C NMR) and high performance liquid chromatography electrospray ionization mass spectrometry (HPLC-ESI-MS) coupled with thiolysis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) analyses. The results showed that these condensed tannins from D. regia possessed structural heterogeneity in monomer units and degree of polymerization. Propelargonidin (PP) and procyanidin (PC) were found in the leaf, fruit, and stem bark of D. regia, while prodelphinidin (PD) was found only in the leaves. The polymer chain lengths of condensed tannins from leaf and fruit organs were detected to be trimers to hexadecamers but from trimers to tridecamers for stem bark. B-type linkages were present in all these compounds. Condensed tannins from different parts of D. regia can be explored as tyrosinase inhibitors and food antioxidants because of their potent antityrosinase and antioxidant activities. The inhibitor concentration leading to 50% enzyme activity (IC(50)) was estimated to be 38 ± 1, 73 ± 2, and 54 ± 1.5 μg/mL for the condensed tannins of leaf, fruit, and stem bark. Condensed tannins extracted from stem bark exhibited the highest antioxidant activity; the DPPH scavenging activity (IC(50)) and the FRAP values were 90 ± 2 μg/mL and 5.42 ± 0.09 mmol AAE/g, respectively.

Rhizodegradation gradients of phenanthrene and pyrene in sediment of mangrove (Kandelia candel (L.) Druce)

A greenhouse experiment was conducted to evaluate degradation gradient of spiked phenanthrene (Ph, 10 mg kg(-1)) and pyrene (Py, 10 mg kg(-1)) in rhizosphere of mangrove Kandelia candel (L.) Druce. Rhizosphere model system was set up using a self-design laminar rhizoboxes which divided into eight separate compartments at various distances from the root surface. After 60 days of plant growth, presence of the plant significantly enhanced the dissipation of Ph (47.7%) and Py (37.6%) from contaminated sediment. Higher degradation rates of the PAHs were observed at 3mm from the root zone (56.8% Ph and 47.7% Py). The degradation gradient followed the order: near rhizosphere>root compartment>far-rhizosphere soil zones for both contaminants where mangrove was grown. Contribution of direct plant uptake and accumulation of Ph and Py were very low compared to the plant enhanced dissipation. By contrast, plant-promoted biodegradation was the predominant contribution to the remediation enhancement. The correlation analysis indicates a negative relation between biological activities (microbial biomass carbon, dehydrogenase, urease, and phosphatase activity) and residual concentrations of Ph and Py in planted soils. Our results suggested that mangrove rhizosphere was effective in promoting the depletion of aromatic hydrocarbons in contaminated sediments.

Analysis of community structure of a microbial consortium capable of degrading benzo(a)pyrene by DGGE.

A microbial consortium was obtained by enrichment culture of sea water samples collected from Botan oil port in Xiamen, China, using the persistent high concentration of a mixture of polycyclic aromatic hydrocarbons enrichment strategy. Denaturing gradient gel electrophoresis (DGGE) was used to investigate the bacterial composition and community dynamic changes based on PCR amplification of 16S rRNA genes during batch culture enrichment. Using the spray-plate method, three bacteria, designated as BL01, BL02 and BL03, which corresponded to the dominant bands in the DGGE profiles, were isolated from the consortium. Sequence analysis showed that BL01, BL02 and BL03 were phylogenetically close to Ochrobactrum sp., Stenotrophomonas maltophilia and Pseudomonas fluorescens, respectively. The degradation of benzo(a)pyrene (BaP), a model high-molecular-weight polycyclic aromatic hydrocarbon (HMW PAH) compound was investigated using individual isolates, a mixture of the three isolates, and the microbial consortium (BL) originally isolated from the oil port sea water. Results showed that the order of degradative ability was BL>the mixture of the three isolates>individual isolates. BL degraded 44.07% of the 10 ppm BaP after 14 days incubation, which showed the highest capability for HMW PAH compound degradation.Our results revealed that this high selective pressure strategy was feasible and effective in enriching the HMW PAH-degraders from the original sea water samples.

Contamination and potential biodegradation of polycyclic aromatic hydrocarbons in mangrove sediments of Xiamen, China.

Five stations were established in the Fenglin mangrove area of Xiamen, China to determine the concentrations of polycyclic aromatic hydrocarbons (PAHs) and the numbers of PAH-degrading bacteria in surface sediments. Assessing the biodegradation potential of indigenous microorganisms and isolating the high molecule weight (HMW)-PAH degrading bacteria was also one of the aims of this work. The results showed that the total PAH concentration of sediments was 222.59 ng g(-1) dry weight, whereas the HMW-PAH benzo(a)pyrene (BaP) had the highest concentration among 16 individual PAH compounds. The variation in the numbers of PAH-degrading bacteria was 2.62 x 10(2)-5.67 x 10(4)CFU g(-1) dry weight. The addition of PAHs showed a great influence in increasing the microbial activity in mangrove sediments. A bacterial consortium, which could utilize BaP as the sole source of carbon and energy, and which was isolated from mangrove sediments and enriched in liquid medium for nearly one year degraded 32.8% of BaP after 63 days incubation.

Silicon Alleviation of Cadmium Toxicity in Mangrove ( Avicennia marina ) in Relation to Cadmium Compartmentation

Mangrove plants seem to be highly tolerant of high levels of heavy-metal pollution. Recently, some researchers have focused on the mechanisms involved in their metal uptake and tolerance. However, the important mechanisms involved are still only partly understood. This investigation studied whether silicon (Si) affected cadmium (Cd) subcellular distribution in the leaves and root tips of Avicennia marina (Forsk.) Vierh seedlings, resulting in the amelioration of the toxicity of Cd. The results showed that Si partly overcame the reduction in growth due to Cd. This amelioration was correlated with a reduction in Cd uptake and alteration of Cd subcellular distribution. The mechanisms of Si amelioration of Cd stress were tissue dependent. In the leaves and root tips, Si reduced Cd concentration in subcellular fractions, Cd mobility, and the concentration of biologically active Cd in the cell wall active space. Si did not change the distribution of Cd between compartments in the leaves, but it increased the proportion of Cd in the cell walls and reduced the proportion of Cd in the symplast of the root tips.

Formation of iron plaque on mangrove Kandalar. Obovata (S.L.) root surfaces and its role in cadmium uptake and translocation.

In this study, a pot experiment was conducted to investigate the formation of iron plaque under Cd stress and its role in Cd uptake and translocation by mangrove Kandalar. Obovata (S.L.). Results showed: 1. the Fe in dithionite–citrate–bicarbonate (DCB) extracts increased with an increasing rate of Cd treatments. 2. the Cd in DCB extracts and in roots and above-ground tissues significantly increased with an increasing Cd application; 3. significant positive correlation between concentration of Cd and Fe in DCB extracts existed (p < 0.05); and that 4. the proportion of Cd in DCB extracts was significantly lower than that in roots or above-ground tissues (p < 0.001). In conclusion, formation of Fe plaque can precipitate Cd on root surfaces and impede its uptake and translocation in Kandalar. Obovata (S.L.). However, in comparison with root tissues, Fe plaque is of little significance. It is the mangrove root tissue that acts as the main buffer to Cd uptake and translocation.

Mangrove-Derived Organic Carbon in Sediment from Zhangjiang Estuary (China) Mangrove Wetland

Abstract The purpose of this study was to characterize mangrove-derived organic matters in wetland sediments and to establish a quantitative differentiation between mangrove-derived organic matter and other organic matter source(s) in the Zhangjiang Estuary mangrove wetland, southern China. Total organic carbon, total nitrogen, carbon/nitrogen ratio, and stable carbon isotopic compositions were measured in surface sediments, three sediment cores (in pure forest of Kandelia candel, Aegiceras corniculatum, and Avicennia marina, respectively), and mangrove plant samples collected from mangrove wetlands. A mixing model was applied to calculate the contribution of the mangrove-derived organic matter in sediment. The mangrove-derived organic matter in three sediment cores from the mangrove wetland were distinguished quantitatively. Our results indicated that organic matter preserved in the sediments was not predominantly composed of the mangrove-derived organic matter in the study areas. The in situ contribution of mangrove plant carbon to sediment organic matter differed between the three core samples. The composition of the mangrove-derived organic matter is 6.36%, on average, in K. candel pure forest, which is much lower than the values in A. marina and A. corniculatum pure forest (21.95% and 36.88%, respectively).

Phosphorus and cadmium interactions in Kandelia obovata (S. L.) in relation to cadmium tolerance.

This study focused on the cadmium (Cd) tolerance of mangroves with application of phosphate (P) in order to explore whether exogenous P can alleviate Cd stress on these intertidal species. Kandelia obovata (S. L.) seedlings were cultivated in rhizoboxes under different levels of Cd and P concentrations. The speciation distributions of Cd in the rhizosphere and non-rhizosphere sediments were examined by sequential extraction procedures; organic acid in plant tissues and soil solution was measured by high-performance liquid chromatography; Cd and P accumulation in the plants was also determined. Results showed that considerable differences existed in Cd speciation distributions between rhizosphere and non-rhizosphere sediments. Root activity influenced the dynamics of Cd, P application increased the organic acid content in root tissues, P also increased Cd accumulation in roots whilst lowering Cd translocation from root to the above-ground tissues, and a significant positive correlation was found between Cd and P in roots (r = 0.905). It is postulated that Cd detoxification of K. obovata (S. L.) is associated with higher Cd immobilization in the presence of higher P and organic acid contents in root tissue.