Antibiofilm activity substances derived from coral symbiotic bacterial extract inhibit biofouling by the model strain Pseudomonas aeruginosa PAO1.

The mitigation of biofouling has received significant research attention, with particular focus on non-toxic and sustainable strategies. Here, we investigated quorum sensing inhibitor (QSI) bacteria as a means of controlling biofouling in a laboratory-scale system. Approximately, 200 strains were isolated from coral (Pocillopora damicornis) and screened for their ability to inhibit quorum sensing (QS). Approximately, 15% of the isolates exhibited QSI activity, and a typical coral symbiotic bacterium, H12-Vibrio alginolyticus, was selected in order for us to investigate quorum sensing inhibitory activity further. Confocal microscopy revealed that V. alginolyticus extract inhibited biofilm formation from Pseudomonas aeruginosa PAO1. In addition, the secondary metabolites of V. alginolyticus inhibited PAO1 virulence phenotypes by downregulating motility ability, elastase activity and rhamnolipid production. NMR and MS spectrometry suggested that the potential bioactive compound involved was rhodamine isothiocyanate. Quantitative real-time PCR indicated that the bacterial extract induced a significant downregulation of QS regulatory genes (lasB, lasI, lasR, rhlI, rhlR) and virulence-related genes (pqsA, pqsR). The possible mechanism underlying the action of rhodamine isothiocyanate analogue involves the disruption of the las and/or rhl system of PAO1. Our results highlight coral microbes as a bioresource pool for developing QS inhibitors and identifying novel antifouling agents.

Anti-quorum Sensing Activities of Selected Coral Symbiotic Bacterial Extracts From the South China Sea.

The worldwide increase in antibiotic-resistant pathogens means that identification of alternative antibacterial drug targets and the subsequent development of new treatment strategies are urgently required. One such new target is the quorum sensing (QS) system. Coral microbial consortia harbor an enormous diversity of microbes, and are thus rich sources for isolating novel bioactive and pharmacologically valuable natural products. However, to date, the versatility of their bioactive compounds has not been broadly explored. In this study, about two hundred bacterial colonies were isolated from a coral species (Pocillopora damicornis) and screened for their ability to inhibit QS using the bioreporter strain Chromobacterium violaceum ATCC 12472. Approximately 15% (30 isolates) exhibited anti-QS activity, against the indicator strain. Among them, a typical Gram-positive bacterium, D11 (Staphylococcus hominis) was identified and its anti-QS activity was investigated. Confocal microscopy observations showed that the bacterial extract inhibited the biofilm formation of clinical isolates of wild-type P. aeruginosa PAO1 in a dose-dependent pattern. Chromatographic separation led to the isolation of a potent QS inhibitor that was identified by high-performance liquid chromatography-mass spectrometry (HPLC-MS) and nuclear magnetic resonance (NMR) spectroscopy as DL-homocysteine thiolactone. Gene expression analyses using RT-PCR showed that strain D11 led to a significant down-regulation of QS regulatory genes (lasI, lasR, rhlI, and rhlR), as well as a virulence-related gene (lasB). From the chemical structure, the target compound (DL-homocysteine thiolactone) is an analog of the acyl-homoserine lactones (AHLs), and we presume that DL-homocysteine thiolactone outcompetes AHL in occupying the receptor and thereby inhibiting QS. Whole-genome sequence analysis of S. hominis D11 revealed the presence of predicted genes involved in the biosynthesis of homocysteine thiolactone. This study indicates that coral microbes are a resource bank for developing QS inhibitors and they will facilitate the discovery of new biotechnologically relevant compounds that could be used instead of traditional antibiotics.

[Roles of microbes in matter cycles in phycosphere niche.] / å¾®ç”Ÿç‰©åœ¨è—»é™ çŽ¯å¢ƒä¸­çš„ç‰©è´¨å¾ªçŽ¯ä½œç”¨.

Phytoplankton is the main driver of marine primary production and matter cycles. Their ecological functions have closely linked to the associated microbes. Although microbial biodiversity is high in all kinds of algal hosts (such as dinoflagellate, diatoms and blue-green algae), some he-terotrophic bacteria (Alphaproteobacteria, Gammaproteobacteria, Flavobacteria, and Actinobacteria) often appear as the dominant communities. In algae-bacteria symbiosis, microbes play important ecological roles, such as regulating microbial food web, mediating the energy flow & nutrient cycling, and maintaining the balance of ecological system. In this review, we summarized the bacterial functions in phycosphere environment, and discussed their contribution to biogeochemical cycle and co-evolution. Particularly, we attempted to take Flavobacteria and Roseobacters as the examples to reveal the metabolic behavior and survive strategies, for better understanding the ecological cha-racterization and co-evolution of "resident species" in phycosphere niche.

[Sapflow characteristics of Kandelia obovata and their controlling factors in Zhangjiang estuary, China.] / ä¸­å›½æ¼³æ±Ÿå£çº¢æ ‘æ¤ç‰©ç§‹èŒ„èŒŽæµç‰¹å¾åŠå ¶å½±å“å› å­.

In this study, the Grainer's thermal dissipation probe method was applied to monitor sap flux density (SFD) of a mangrove species Kandelia obovata over a period of one year (2010-10-2011-10) in Zhangjiangkou Mangrove National Nature Reserve, Fujian, China. The results showed that both season and diameter class exerted significant effects on the SFD of K. obovata trees. In summer, when the diameter at breast height (DBH) reached 8-10 cm, the highest SFD was found at a depth of 2 cm with a value of 38.21 g·m-2·s-1, which was comparable with those for other mangrove tree species and forested wetland tree species. The mean whole tree transpiration (i.e. daily water use) of all stem size classes demonstrated large changes from winter to summer, increased from 0.14 to 0.19 kg·d-1 in small trees (S, DBH=2-4 cm), from 0.94 to 1.45 kg·d-1 in medium trees (M, DBH=4-8 cm) and from 1.96 to 3.43 kg·d-1 in large ones (L, DBH=8-10 cm). The daily transpiration of K. obovata stand was calculated by summing all size classes, which was then summed up for entire year to estimate annual transpiration of entire K. obovata forest, which was about 100.38 mm, less than 6% of local annual precipitation. Key environmental factors all had significant effects (all P<0.001) on the stand transpiration rate (Es) of K. obovata forest, and photosynthetically active radiation (PAR) and vapor pressure deficit (VPD) were the main driving factors, which explained 60%-92% seasonal variation of Es. The PAR and VPD had larger effects on the Es in summer than that in winter. In addition, we observed an obvious time lag phenomenon in the relationship between Es and PAR or VPD, which should be taken into account when explaining seasonal variation of Es in K. obovata forest.

[Current status of mangrove germplasm resources and key techniques for mangrove seedling propagation in China].

Mangrove germplasm and nursery operation are the foundations of all mangrove ecological restoration projects. Based on the existing literatures and our own experiences, and by using cluster analysis and other methods, this paper assessed the current status of the mangrove germplasm resources and the key techniques for mangrove seedlings propagation in China. In China, the mangrove communities could be divided into 4 types, including low temperature tolerant widespread type, widespread type, thermophilic widespread type, and tropical type, and the mangrove distribution sites could be divided into 5 regions, i. e., eastern Hainan coast, Beibuwan Gulf coast, Pearl River estuary and eastern Guangdong coast, southern Fujian and Taiwan coast, and eastern Fujian and southern Zhejiang coast. The mangroves in Beibuwan Gulf coast region took up 75.3% of the total mangrove germplasm resources in the country. At present, the percentage of the mangrove species applied for seedling propagation in China was estimated at 52.6%, most of which were of viviparous species. The six key steps in mangrove nursery operation included the selection of proper seedling propagation methods, the collection and storage of seeds or propagules, the ways of raising seedlings, the management of water and salinity, the control of diseases and pests, and the prevention of cold damage during winter. The structure, functions, and applieations of the present five types of mangrove nurseries, including dry land nursery, mangrove tidal nursery, mudflat nursery, Jiwei pond nursery, and Spartina mudflat nursery, were also analyzed, which could provide guidance for the integrated management of mangrove ecological restoration engineering.

Hydrogen sulphide enhances photosynthesis through promoting chloroplast biogenesis, photosynthetic enzyme expression, and thiol redox modification in Spinacia oleracea seedlings.

Hydrogen sulphide (H(2)S) is emerging as a potential messenger molecule involved in modulation of physiological processes in animals and plants. In this report, the role of H(2)S in modulating photosynthesis of Spinacia oleracea seedlings was investigated. The main results are as follows. (i) NaHS, a donor of H(2)S, was found to increase the chlorophyll content in leaves. (ii) Seedlings treated with different concentrations of NaHS for 30 d exhibited a significant increase in seedling growth, soluble protein content, and photosynthesis in a dose-dependent manner, with 100 µM NaHS being the optimal concentration. (iii) The number of grana lamellae stacking into the functional chloroplasts was also markedly increased by treatment with the optimal NaHS concentration. (iv) The light saturation point (Lsp), maximum net photosynthetic rate (Pmax), carboxylation efficiency (CE), and maximal photochemical efficiency of photosystem II (F(v)/F(m)) reached their maximal values, whereas the light compensation point (Lcp) and dark respiration (Rd) decreased significantly under the optimal NaHS concentration. (v) The activity of ribulose-1,5-bisphosphate carboxylase (RuBISCO) and the protein expression of the RuBISCO large subunit (RuBISCO LSU) were also significantly enhanced by NaHS. (vi) The total thiol content, glutathione and cysteine levels, internal concentration of H(2)S, and O-acetylserine(thiol)lyase and L-cysteine desulphydrase activities were increased to some extent, suggesting that NaHS also induced the activity of thiol redox modification. (vii) Further studies using quantitative real-time PCR showed that the gene encoding the RuBISCO large subunit (RBCL), small subunit (RBCS), ferredoxin thioredoxin reductase (FTR), ferredoxin (FRX), thioredoxin m (TRX-m), thioredoxin f (TRX-f), NADP-malate dehydrogenase (NADP-MDH), and O-acetylserine(thiol)lyase (OAS) were up-regulated, but genes encoding serine acetyltransferase (SERAT), glycolate oxidase (GYX), and cytochrome oxidase (CCO) were down-regulated after exposure to the optimal concentration of H(2)S. These findings suggest that increases in RuBISCO activity and the function of thiol redox modification may underlie the amelioration of photosynthesis and that H(2)S plays an important role in plant photosynthesis regulation by modulating the expression of genes involved in photosynthesis and thiol redox modification.

Effects of environmental stresses on the responses of mangrove plants to spent lubricating oil.

The influence of different environmental stresses, including salinity (5-35‰), tidal cycle (6/6, 12/12 and 24/24 h of high/low tidal regimes) and nutrient addition (1-6 times background nitrogen and phosphorus content) on Bruguiera gymnorrhiza and Aegiceras corniculatum grown in sediment contaminated with spent lubricating oil (7.5 L m(-2)) were investigated. The oil-treated 1-year-old mangrove seedlings subject to low (5‰) and high (35‰) salinity had significantly more reduction in growth, more release of superoxide radical (O2·-) and higher activity of superoxide dismutase (SOD) than those subject to moderate salinity (15‰). Extended flooding (24/24 h of high/low tidal regime) enhanced O2·- release and malondialdehyde (MDA) content in both oil-treated species but had little negative effects on biomass production (P>0.05) except the stem of A. corniculatum (P=0.012). The addition of nutrients had no beneficial or even posed harmful effects on the growth and cellular responses of the oil-treated seedlings.

Antioxidant tannins from stem bark and fine root of Casuarina equisetifolia.

Structures of condensed tannins from the stem bark and fine root of Casuarina equisetifolia were identified using MALDI-TOF MS and HPLC analyses. The condensed tannins from stem bark and fine root consist predominantly of procyanidin combined with prodelphinidin and propelargonidin, and epicatechin is the main extension unit. The condensed tannins had different polymer chain lengths, varying from trimers to tridecamer for stem bark and to pentadecamer for fine root. The antioxidant activities were measured by two models: 1,1-diphenyl-2- picrylhydrazyl (DPPH) radical scavenging activity and ferric reducing/ antioxidant power (FRAP). The condensed tannins extracted from C. equisetifolia showed very good DPPH radical scavenging activity and ferric reducing/ antioxidant power, suggesting that these extracts may be considered as new sources of natural antioxidants for food and nutraceutical products.

[Temporal and spatial variations of soil respiration in an Artemisia ordosica shrubland ecosystem in Kubuqi Desert].

Based on the dynamic measurements of soil respiration using a closed dynamic chamber and its related environmental factors in a desert shrubland ecosystem regularly during the growing season (May-September) of 2006, we studied the diurnal and seasonal variations of soil respiration of two different land cover soils and their responses to soil temperature, soil water content and biotic factors. The objective was to evaluate the temporal and spatial patterns of soil respiration and their responsible factors in Artemisia ordosica shrubland in Kubuqi Desert, Inner Mongolia, China. The diurnal variation of soil respiration showed an asymmetric single-peak pattern, with the peak value occurring around 12:00. Soil respiration fluctuated greatly during the growing season, reaching peak values in July-August. There was a significant linear relationship between soil respiration rate and soil water content at 10 cm depth. Most of the seasonal variation in soil respiration (75%-77%) could be explained by the variation in soil water content. The mean soil respiration under the shrub canopy was (155.58 +/- 15.20) mg x (m2 x h)(-1), which was significantly higher than that for the bare ground between the shrubs (110.50 +/- 6.77) mg x (m2 x h)(-1). The sensitivity of soil respiration to soil water content was also significantly higher for the soils under the canopy than for the bare ground soils. The spatial variation of soil respiration was caused mainly by the root biomass, which can be explained about 43% of heterogeneity. The results suggest that variation on a small time and space scales must be taken into consideration when estimating soil CO2 efflux in the desert ecosystems.

Leaf respiratory CO2 is 13 C-enriched relative to leaf organic components in five species of C3 plants.

• Here, we compared the carbon isotope ratios of leaf respiratory CO2 (δ13 CR ) and leaf organic components (soluble sugar, water soluble fraction, starch, protein and bulk organic matter) in five C3 plants grown in a glasshouse and inside Biosphere 2. One species, Populus deltoides, was grown under three different CO2 concentrations. • The Keeling plot approach was applied to the leaf scale to measure leaf δ13 CR and these results were compared with the δ13 C of leaf organic components. • In all cases, leaf respiratory CO2 was more 13 C-enriched than leaf organic components. The amount of 13 C enrichment displayed a significant species-specific pattern, but the effect of CO2 treatment was not significant on P. deltoides. • In C3 plant leaves, 13 C-enriched respiratory CO2 appears widespread. Among currently hypothesized mechanisms contributing to this phenomenon, non-statistical carbon isotope distribution within the sugar substrates seems most likely. However, caution should be taken when attempting to predict the δ13 C of leaf respiratory CO2 at the ecosystem scale by upscaling the relationship between leaf δ13 CR and δ13 C of leaf organic components.