Assessing ecological health of mangrove ecosystems along South China Coast by the pressure-state-response (PSR) model.

The pressure-state-response (PSR) model was applied to establish a mangrove ecosystem health evaluation system combined with analytical hierarchy process (AHP) in this paper. The mangrove wetlands are divided into five ecological levels: excellent health, good health, health, sub-health and morbidity, which is based on the comprehensive health index (CHI) value. Twelve representative sites were selected for sampling to assess the ecological health condition of mangroves. As a result, the ecological health level of Gaoqiao mangrove area is excellent health; the ecological health level of Taiping mangrove area is good health; the ecological health level of Huguang and Qi'ao mangrove area is health; the ecological health level of Techeng and He'an mangrove area is sub-health; the ecological health level of Huidong mangrove area is morbidity. These results will give some advises for ecological protection and biological resource sustainable development of mangrove ecosystem in China.

Comparative physiological and proteomic analyses of mangrove plant Kandelia obovata under cold stress.

Cold events had broadly affected the survival and geographic distribution of mangrove plants. Kandelia obovata, has an excellent cold tolerance as a true halophyte and widespread mangrove species. In this study, physiological characters and comparative proteomics of leaves of K. obovata were performed under cold treatment. The physiological analysis showed that K. obovata could alleviate its cold-stress injuries through increasing the levels of antioxidants, the activities of related enzymes, as well as osmotic regulation substances (proline). It was detected 184 differentially expressed protein spots, and of 129 (70.11%) spots were identified. These proteins have been involved in several pathways such as the stress and defense, photosynthesis and photorespiration, signal transduction, transcription factors, protein biosynthesis and degradation, molecular chaperones, ATP synthesis, the tricarboxylic acid (TCA) cycle and primary metabolisms. The protein post-translational modification may be a common phenomenon and plays a key role in cold-response process in K. obovata. According to our precious work, a schematic diagram was drawn for the resistance or adaptation strategy of mangrove plants under cold stress. This study provided valuable information to understand the mechanism of cold tolerance of K. obovata.

Bacterial community variations in the South China Sea driven by different chemical conditions.

In this study, Illumina MiSeq sequencing of the 16 S rRNA gene was used to describe the bacterial communities in the South China Sea (SCS) during the southwest monsoon period. We targeted different regions in the SCS and showed that bacterial community was driven by the effects of the river, upwelling, and mesoscale eddy through changing the environmental factors (salinity, temperature, and nutrients). Distinct bacterial communities were observed among different chemical conditions, especially between the estuary and the open sea. The abundance of Burkholderiales, Frankiales, Flavobacteriales, and Rhodobacterales dominated the estuary and its adjacent waters. Bacteria in cyclonic eddy were dominated by Methylophilales and Pseudomonadales, whereas Prochlorococcus, SAR11 clade, and Oceanospirillales had relatively high abundance in the anticyclonic eddy. Overall, the abundance of specific phylotypes significantly varied among samples with different chemical conditions. Chemical conditions probably act as a driver that shapes and controls the diversity of bacteria in the SCS. This study suggests that the interaction between microbial and environmental conditions needs to be further considered to fully understand the diversity and function of marine microbes.

Isolation and expression analysis of two novel C-repeat binding factor (CBF) genes involved in plant growth and abiotic stress response in mangrove Kandelia obovata.

Kandelia obovata is one of the cold tolerant mangrove plants along the China coast. To reveal the cold tolerant mechanism of K. obovata, the present work isolated two CBF/DREB1 genes (designated KoCBF1 and KoCBF3) from cold-stressed K. obovata and characterized their expression profiles in various organs and in response to multiple abiotic stresses. The deduced proteins of KoCBF1 and 3 all contain specific features of CBFs, and show high similarity to AmCBF1 and 3 from Avicennia marina, respectively. Different expression patterns of the two CBF orthologous under various abiotic stresses and exogenous hormone suggested that they may have different regulators and be involved in different regulatory pathway. The high basal and cold induced expression of the two genes indicated that they may all play important roles in growth and cold resistance of plants. The significant induction of KoCBF3 after salt and lead (Pb2+) treatments suggested that this CBF gene may also participate in response to salinity and heavy metal stresses. This study will provide a better understanding of CBF-regulated stress-resistant mechanism, which may be benefit in mangrove biotechnological breeding, high-latitude transplanting, and bioremediation of heavy metal pollutions.

Isolation and expression analysis of a CBF transcriptional factor gene from the mangrove Bruguiera gymnorrhiza.

The present work isolated a CBF/DREB1 gene from mangrove Bruguiera gymnorrhiza (BgCBF1) and compared its expression levels in various tissues under normal condition and cold stress, and in leaves exposed to various environmental stimuli. Results showed that the BgCBF1 deduced protein showed almost 100% similarities to that of AcCBF1 from Aegiceras corniculatum and AmCBF1 from Avicennia marina. Real-time quantitative PCR analysis showed that BgCBF1 gene displayed constitute expression in leaf, stem and root samples of plantlets under normal condition, but with different expression levels and tissue preference. When exposed to cold, BgCBF1 could be rapidly, slightly and transiently induced in all tissues. Furthermore, the BgCBF1 gene in leaves displayed a transient and small induction after salt and drought (PEG) exposure, while exhibited relatively high up-regulated expression after the phytohormone abscisic acid (ABA) treatment. These results suggest that the BgCBF1 gene may participate in the ABA mediated development and protection of plant against cold and drought. Further studies on its promoters and downstream genes will be needed to better understand its functions.

Dynamics of radial oxygen loss in mangroves subjected to waterlogging.

Tidal flooding can directly result in oxygen (O2) shortage, however the functions of root aeration in flooding tolerance and O2 dynamics within mangroves are still poorly understood. Thus, in this study, the correlations among waterlogging tolerance, root porosity and O2 movement within the plants were investigated using two mangrove species (Aegiceras corniculatum and Bruguiera gymnorrhiza) and a semi-mangrove Heritiera littoralis. Based on the present data, the species A. corniculatum and B. gymnorrhiza, which possessed higher root porosity, exhibited higher waterlogging tolerance, while H. littoralis is intolerant. Increased root porosity, leaf stoma, and total ROL were observed in the roots of A. corniculatum and B. gymnorrhiza growing in stagnant solution when compared to respective aerated controls. As for ROL spatial pattern along roots, external anaerobic condition could promote ROL from apical root regions but reduce ROL from basal roots, leading to a 'tighter barrier'. In summary, the present study indicated that the plants (e.g., A. corniculatum and B. gymnorrhiza) prioritized to ensure O2 diffusion towards root tips under waterlogging by increasing aerenchyma formation and reducing O2 leakage at basal root regions.

Distribution patterns and source identification for heavy metals in Mirs Bay of Hong Kong in China.

Sediment quality caused by heavy metals was investigated in the Mirs Bay and Tolo Harbor, Hong Kong, China. Samples were collected in January and July, 2010. One-way analysis of variance showed that sediment quality variables (Fe, Zn, Mn, Pb, V, Cu, Cr, Ba, Ni and As) were significantly different (p < 0.05) among the sampling areas, whereas the average concentration of V, Eh and Ba exhibited the significant seasonal variations (p < 0.05) between January and July. The spatial pattern of heavy metals (Pb, Zn and Cu) can probably be attributed to anthropogenic and tidal flushing influence in the harbor. Both geo-accumulation index (Igeo) and enrichment factor (EF) were used to identify the metal pollution level and its related source. Pb, Zn, and Cu are considered as "polluted metal" in Tolo Harbor. Cluster analysis (CA) identified three distinct clusters with the Tolo Habor and Shatou Jiao, the inner bay and the south part of the bay. Principal component analysis (PCA) identified the spatial patterns and their affected parameters in the studying area. Results showed metals distribution in Mirs Bay and its adjacent area is principally affected by human activities such as marineculture, dumping, located mostly in Tolo Harbor and Shatou Jiao, where was closely related with anthropogenic influence. While the monitoring stations including MS13-MS16 and MS8 locating in the south part of the studying area might be corresponded to natural influence.

Phytoplankton community, structure and succession delineated by partial least square regression in Daya Bay, South China Sea.

Daya Bay is facing the influence of human activities and nature changes, which result in phytoplankton adjusting to the changing environment. The data about environmental changes and phytoplankton were obtained from four seasonal cruises in 2013 in the bay. It is helpful to explore seasonal succession of phytoplankton driven by the determining environmental factors in this bay. Temperature is a significant indicator of season change. The limiting factor of phytoplankton growth totally changed from P (PO4-P) limiting during the southwest monsoon to Si (SiO3-Si) limiting during northeast monsoon. The order of diatoms and dinoflagellates was the dominant phytoplankton groups in Daya Bay. The dominant species included chain-forming diatoms (Skeletonema, Pseudo-nitzschia, Thalassionema, Chaetoceros and Rhizosolenia) were found all the year round and filamentous cyanobacteria (Trichodesmium) in spring and autumn. Partial least square regression (PLS) found that salinity, temperature and nutrients were important driving force for phytoplankton seasonal succession.

Ecophysiological differences between three mangrove seedlings (Kandelia obovata, Aegiceras corniculatum, and Avicennia marina) exposed to chilling stress.

Although the cold-resistant ability of mangroves varies greatly with species, the physiological mechanism remains unclear. The chilling stress effects on morphological changes, photosynthetic pigments, reactive oxygen species (ROS), malondialdehyde (MDA) and several antioxidants, were studied in leaves of three mangrove seedlings (Kandelia obovata, Aegiceras corniculatum and Avicennia marina). Results showed that both K. obovata and A. corniculatum exhibited lighter chilling damage, lower chilling injury rates and higher survival rates compared to A. marina. Reductions of chlorophylls (Chls) were observed in all the three mangroves, and the highest was detected in A. marina. Significant increases in content of ROS (hydrogen peroxide, H2O2; hydroxyl radicals, OH⋅) and MDA were observed in both A. marina and A. corniculatum, whereas chilling stressed K. obovata showed a decrease in H2O2 content, constant OH⋅ level and instantaneous increase of MDA. The contents of proline and water-soluble protein exhibited similar stress-time dependent increases in all mangroves, while A. corniculatum showed the highest increase of proline and relatively higher increase of water-soluble protein. The catalase activities significantly decreased with stress time in all mangroves, while K. obovata showed the least reduction. An increase in ascorbic acid (AsA) content and activities of superoxide dismutase, peroxidase (POD), and ascorbate peroxidase (APX) were also detected in all the three mangroves, while K. obovata showed the highest increases. These results indicate that chilling-tolerance of mangroves is associated with the efficiency of antioxidants, as confirmed by principal component analysis. The AsA, APX and POD in K. obovata may play more important role in control of oxidative stresses than those in the other two species. Furthermore, the higher cold-resistance of A. corniculatum compared to A. marina may be partly associated with its higher proline accumulation. The results indicate that enzymatic and non-enzymatic antioxidants (POD, APX, AsA, proline and Car) play key roles in scavenging of excess ROS in mangroves. Further studies focusing on these stress-responsive genes will enable better understanding of the cold-resistance mechanism from molecular level.

Spatial and vertical distribution of bacterial community in the northern South China Sea.

Microbial communities are highly diverse in coastal oceans and response rapidly with changing environments. Learning about this will help us understand the ecology of microbial populations in marine ecosystems. This study aimed to assess the spatial and vertical distributions of the bacterial community in the northern South China Sea. Multi-dimensional scaling analyses revealed structural differences of the bacterial community among sampling sites and vertical depth. Result also indicated that bacterial community in most sites had higher diversity in 0-75 m depths than those in 100-200 m depths. Bacterial community of samples was positively correlation with salinity and depth, whereas was negatively correlation with temperature. Proteobacteria and Cyanobacteria were the dominant groups, which accounted for the majority of sequences. The α-Proteobacteria was highly diverse, and sequences belonged to Rhodobacterales bacteria were dominant in all characterized sequences. The current data indicate that the Rhodobacterales bacteria, especially Roseobacter clade are the diverse group in the tropical waters.

Pb uptake and tolerance in the two selected mangroves with different root lignification and suberization.

Metal pollution has been widely reported in mangrove wetlands; however, the mechanisms involved in metal detoxification by mangroves are still poorly understood. This study aimed to investigate the possible function of root lignification/suberization on Pb uptake and tolerance in mangroves. Two mangroves, Acanthus ilicifolius and Rhizophora stylosa with different root lignification/suberization were selected as plant materials; the former exhibits a thin exodermis and low lignification/suberization, while the latter possesses a thick exodermis and high lignification/suberization. A pot trial with addition of Pb was conducted to investigate the differences in Pb uptake and tolerance between the two mangroves. The experiment of rhizobox was designed to explore Pb dynamics and availabilities in the rhizosphere soils, besides, the ability of Pb uptake by the excised roots and X-ray analysis for Pb distribution within roots were also detected. The results revealed that R. stylosa exhibited relatively higher Pb tolerance together with less Pb accumulations when compared to A. ilicifolius. For both species, lower proportion of exchangeable and Carbonate Pb and higher higher Fe-Mn oxides Pb were observed in the rhizosphere zone when compared to the respective non-rhizosphere zone. The results from metal uptake by the excised roots and X-ray analysis clearly showed that the thick lignified/suberized exodermis of R. stylosa could more efficiently delay Pb entering into the roots, leading to less Pb accumulation. In summary, the present study proposes a barrier property of the lignified/suberized exodermis in dealing with the stresses of Pb.

Distribution and sources of the polycyclic aromatic hydrocarbons in the sediments of the Pearl River estuary, China.

The Pearl River delta, one of the most prosperous economically region in China, has experienced significant contaminant inputs. However, the dynamics of pollutants in the Pearl River estuary and the adjacent coastal areas are still unclear at present. In the paper, distribution and sources of polycyclic aromatic hydrocarbons (PAHs) were investigated in the surface sediments of the Pearl River estuary. The total PAHs concentrations ranged from 126.08 to 3828.58 ng/g with a mean value of 563.52 ng/g, whereas the highest PAHs were observed in Guangzhou channel. Among the U.S. Environmental Protection Agency's 16 priority PAHs, PAHs with 3-4 rings exhibited relative higher levels. A positive relationship was found between PAHs and total organic carbon. The source analysis further showed that the major sources of PAHs in the Pearl River estuary were originated from the pyrolytic inputs, reflecting a mixed energy structure such as wood, coal and petroleum combustion. In summary, although PAHs in Lingding Bay and the adjacent coastal areas of the Pearl River estuary exhibited a relatively low pollution level, the relatively high pollution level of PAHs in Guangzhou channel will be attended.

Variation of phytoplankton community structure from the Pearl River estuary to South China Sea.

The Pearl River is located in the northern part of South China Sea. The environment of the Pearl River estuary (PRE) is significantly impacted by nutrients from anthropogenic activities. Along the anthropogenic pollution gradient from the PRE to South China Sea, the phylogenetic diversity and biomass of phytoplankton was examined in relation to physic-chemical variables. The richness of rbcL gene was higher in the open sea than the estuary, while the concentration of chlorophyll a (Chl a) was higher in the estuary than in the open sea. The cluster analysis of the sequences data resulted in seven phytoplankton community types and the dominant species of phytoplankton changed from Cryptophytes and Diatoms to Prymnesiophytes and Diatoms along the gradient. The community structure of phytoplankton was shaped by nutrients and salinity. The phytoplankton biomass was significantly positively affected by phosphorus, nitrite and ammonium (P < 0.01) but negatively by salinity (P < 0.05); the phytoplankton diversity was highly positively affected by salinity (P < 0.05) but negatively by silicate and nitrate (P < 0.01; P < 0.05, respectively). Anthropogenic activities played a critical role in the phytoplankton distribution and biomass of the study area. Further research is necessary to reveal the influence mechanism of environmental factors on the phytoplankton.

The diversity of coral associated bacteria and the environmental factors affect their community variation.

Coral associated bacterial community potentially has functions relating to coral health, nutrition and disease. Culture-free, 16S rRNA based techniques were used to compare the bacterial community of coral tissue, mucus and seawater around coral, and to investigate the relationship between the coral-associated bacterial communities and environmental variables. The diversity of coral associated bacterial communities was very high, and their composition different from seawater. Coral tissue and mucus had a coral associated bacterial community with higher abundances of Gammaproteobacteria. However, bacterial community in seawater had a higher abundance of Cyanobacteria. Different populations were also found in mucus and tissue from the same coral fragment, and the abundant bacterial species associated with coral tissue was very different from those found in coral mucus. The microbial diversity and OTUs of coral tissue were much higher than those of coral mucus. Bacterial communities of corals from more human activities site have higher diversity and evenness; and the structure of bacterial communities were significantly different from the corals collected from other sites. The composition of bacterial communities associated with same coral species varied with season's changes, geographic differences, and coastal pollution. Unique bacterial groups found in the coral samples from more human activities location were significant positively correlated to chemical oxygen demand. These coral specific bacteria lead to coral disease or adjust to form new function structure for the adaption of different surrounding needs further research.

Molecular Cloning and Expression Analysis of the Typical Class III Chitinase Genes from Three Mangrove Species under Heavy Metal Stress.

Chitinases are considered to act as defense proteins when plants are exposed to heavy metal stresses. Typical class III chitinase genes were cloned from Kandelia obovate, Bruguiera gymnorrhiza, and Rhizophora stylosa by using RT-PCR and RACE and named KoCHI III, BgCHI III, and RsCHI III. Bioinformatics analysis revealed that the three genes encoding proteins were all typical class III chitinases with the characteristic catalytic structure belonging to the family GH18 and located outside the cell. In addition, there are heavy metal binding sites in the three-dimensional spatial structure of the type III chitinase gene. Phylogenetic tree analysis indicated that CHI had the closest relationship with chitinase in Rhizophora apiculata. In mangrove plants, the balance of the oxidative system in the body is disrupted under heavy metal stress, resulting in increased H2O2 content. Real-time PCR illustrated that the expression level under heavy metal stress was significantly higher than that in the control group. Expression levels of CHI III were higher in K. obovate than in B. gymnorrhiza and R. stylosa. With the increase in heavy metal stress time, the expression level increased continuously. These results suggest that chitinase plays an important role in improving the heavy metal tolerance of mangrove plants.

Cloning and Expression of Class I Chitinase Genes from Four Mangrove Species under Heavy Metal Stress.

Chitinases are believed to act as defense proteins when plants are exposed to heavy metal stress. Typical Class I chitinase genes were cloned from Bruguiera gymnorrhiza, Rhizophora stylosa, Kandelia obovata, and Avicennia marina using the methods of reverse-transcription-polymerase chain reaction and rapid amplification of cDNA ends. All four cDNA sequences of chitinase from the mangrove plants were 1092 bp in length and consisted of an open reading frame of 831 bp, encoding 276 amino acids. However, there were differences in the sequences among the four mangrove species. Four gene proteins have a signal peptide, are located in the vacuole, and belong to the GH19 chitinase family. The sequence of chitinase was highly similar to the protein sequences of Camellia fraternal chitinases. A real-time polymerase chain reaction was used to analyze the chitinase expressions of the above four mangrove species exposed to different concentrations of heavy metal at different times. The gene expression of chitinase was higher in Bruguiera gymnorrhiza leaves than in other mangrove plant species. With an increase in heavy metal stress, the expression level of Bruguiera gymnorrhiza increased continuously. These results suggest that chitinase plays an important role in improving the heavy metal tolerance of mangrove plants.

Polymeric carbohydrates utilization separates microbiomes into niches: insights into the diversity of microbial carbohydrate-active enzymes in the inner shelf of the Pearl River Estuary, China.

Polymeric carbohydrates are abundant and their recycling by microbes is a key process of the ocean carbon cycle. A deeper analysis of carbohydrate-active enzymes (CAZymes) can offer a window into the mechanisms of microbial communities to degrade carbohydrates in the ocean. In this study, metagenomic genes encoding microbial CAZymes and sugar transporter systems were predicted to assess the microbial glycan niches and functional potentials of glycan utilization in the inner shelf of the Pearl River Estuary (PRE). The CAZymes gene compositions were significantly different between in free-living (0.2-3 µm, FL) and particle-associated (>3 µm, PA) bacteria of the water column and between water and surface sediments, reflecting glycan niche separation on size fraction and selective degradation in depth. Proteobacteria and Bacteroidota had the highest abundance and glycan niche width of CAZymes genes, respectively. At the genus level, Alteromonas (Gammaproteobacteria) exhibited the greatest abundance and glycan niche width of CAZymes genes and were marked by a high abundance of periplasmic transporter protein TonB and members of the major facilitator superfamily (MFS). The increasing contribution of genes encoding CAZymes and transporters for Alteromonas in bottom water contrasted to surface water and their metabolism are tightly related with particulate carbohydrates (pectin, alginate, starch, lignin-cellulose, chitin, and peptidoglycan) rather than on the utilization of ambient-water DOC. Candidatus Pelagibacter (Alphaproteobacteria) had a narrow glycan niche and was primarily preferred for nitrogen-containing carbohydrates, while their abundant sugar ABC (ATP binding cassette) transporter supported the scavenging mode for carbohydrate assimilation. Planctomycetota, Verrucomicrobiota, and Bacteroidota had similar potential glycan niches in the consumption of the main component of transparent exopolymer particles (sulfated fucose and rhamnose containing polysaccharide and sulfated-N-glycan), developing considerable niche overlap among these taxa. The most abundant CAZymes and transporter genes as well as the widest glycan niche in the abundant bacterial taxa implied their potential key roles on the organic carbon utilization, and the high degree of glycan niches separation and polysaccharide composition importantly influenced bacterial communities in the coastal waters of PRE. These findings expand the current understanding of the organic carbon biotransformation, underlying the size-fractionated glycan niche separation near the estuarine system.

Effects of pyrene on antioxidant systems and lipid peroxidation level in mangrove plants, Bruguiera gymnorrhiza.

The effects of polycyclic aromatic hydrocarbon (PAH) (pyrene) on superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase, peroxidase, malondialdehyde (MDA) and proline were studied in leaves, stems and roots of Bruguiera gymnorrhiza. The results showed that the responses of enzymatic and non-enzymatic antioxidants varied significantly among the three tissues studied. The activities of antioxidant enzymes in PAH-treated stems and roots fluctuated in different stress levels compared to the controls, while the antioxidant enzymes such as SOD, APX in leaves increased when stressed by PAH with a significant positive relation between PAH and leaf SOD or APX activity. Low PAH treatments could also stimulate proline in leaves and stems. MDA content was obviously accumulated in stems and roots under PAH stress while decreased in leaves, indicating that the increased antioxidant enzymes in leaves may partly alleviate lipid peroxidation. For pollution monitoring purpose, SOD and APX in leaves may be potential biomarkers of PAH pollution in intertidal estuaries.

Effects of three different PAHs on nitrogen-fixing bacterial diversity in mangrove sediment.

Polycyclic aromatic hydrocarbons (PAHs) are of great environmental and human health concerns due to their widespread occurrence, persistence and carcinogenic properties. There is now compelling evidence that the mangrove sediment microbial structure is susceptible to PAHs contamination. The study aimed to assess the effects of PAHs on the nitrogen-fixing bacterial community of mangrove sediment. Three types of PAHs, naphthalene (NAP), a two-ring PAH; fluorene (FLU), a three-ring PAH; and pyrene (PYR), a four-ring PAH; were applied at three doses. After 7 and 24 days of incubation, the nitrogen-fixing bacterial population and diversity were evidenced in the nifH gene polymerase chain reaction denaturing gradient gel electrophoresis profile. DGGE pattern shows that the nitrogen-fixing bacterial community changed significantly with the types and doses of PAHs, and the incubation time. As far as single PAH is concerned, high concentration of PAH has larger impact on the nitrogen-fixing bacteria than low concentration of PAH. Besides, among the three types of PAHs, NAP has the greatest short term toxicity; PYR has the strongest long-term impact, whereas FLU has relatively higher long-time effect. Multidimensional scaling analysis and correspondence analysis are two reliable multivariate analysis methods for investigating the relationship between the nitrogen-fixing bacterial community and PAHs contamination. Investigating the effect of PAHs on the nitrogen-fixing bacterial diversity could yield useful information for understanding the process of biogeochemical cycling of nitrogen in mangrove sediment. The present study reveals that nitrogen-fixing bacterial community can be used as an important parameter indicating the impact of PAHs on mangrove sediment ecosystem.

A novel metallothionein gene from a mangrove plant Kandelia candel.

A new metallothionein (MT) gene was cloned from Kandelia candel, a mangrove plant with constitutional tolerance to heavy metals, by rapid amplification of cDNA ends and named KMT, which is composed of two exons and one intron. The full length of KMT cDNA was 728 bp including 121 bp 5' noncoding domain, 240 bp open reading frame and 384 bp 3' termination. The coding region of KMT represented a putative 79 amino acid protein with a molecular weight of 7.75 kDa. At each of the amino- and carboxy-terminal of the putative protein, cysteine residues were arranged in Cys-Cys, Cys-X-Cys and Cys-X-X-Cys, indicating that the putative protein was a novel type 2 MT. Sequence and homology analysis showed the KMT protein sequence shared more than 60 % homology with other plant type 2 MT-like protein genes. At amino acid level, the KMT was shown homology with the MT of Quercus suber (83 %), of Ricinus communis (81 %) and of Arabidopsis thaliana (64 %). Function studies using protease-deficient Escherichia coli strain BL21 Star ™(DE3) confirmed the functional nature of this KMT gene in sequestering both essential (Zn) and non-essential metals (Cd and Hg) and the E. coli BL21 with KMT can live in 1,000 µmol/L Zn, 120 µmol/L Hg, and 2,000 µmol/L Cd. The information could provide more details of the causative molecular and biochemical mechanisms (including heavy metal sequestration) of the KMT in K. candel or a scientific basis for marine heavy-metal environment remediation with K. candel. This study also provides a great significance of protecting mangrove species and mangrove ecosystem.