Enhancing nutrient absorption through the influence of mangrove ecosystem on flow rate and retention time in salt marshes

This study investigates the impact of pneumatophores (the aerial roots of Avicenna marina) on water flow rate, retention time, contact time, and consequently on nutrient absorption through the sediment in sub-tropical salt marshes. The goal is to realize how the density of mangroves in salt marshes influences the kinematic factors of streamflow at estuaries. To this end, a field experiment was carried out to assess nutrient and organic compound levels in the sediment and water samples, spanning six sampling stations along the Chabahar River discharging to the Chabahar Bay, Iran. Then, we delved into the influence of altering environmental parameters, such as density and geometry, on the kinematic features of the flow through statistical analysis and hydraulic modeling. The results showed that the aerial roots reduce the flow rate and increase both retention and contact times. The longest retention time was observed at station #5 due to increased vegetation density and decreased instream velocity. In addition, measurements of total organic matter, total organic carbon, and total nitrogen indicated that an extended contact time resulted in increased absorption flux to the stream by sediments. As a result, pneumatophores can serve as an effective sink for organic matter in ecotones in salt marshes.

Acidity and oxidative potential of atmospheric aerosols over a remote mangrove ecosystem during the advection of anthropogenic plumes

To investigate the acidity and the water-soluble oxidative potential of PM10, during the continental biomass-burning plume transport, a three-year (2018-2020) winter-time campaign was conducted over a pristine island (21.35°N, 88.32°E) of Sundarban mangrove ecosystem situated at the shore of Bay of Bengal. The average PM10 concentration over Sundarban was found to be 98.3 ± 22.2 μg m-3 for the entire study period with a high fraction of non-sea-salt- SO42- and water-soluble organic carbons (WSOC) that originated from the regional solid fuel burning. The thermodynamic E-AIM(IV) model had estimated that the winter-time aerosols over Sundarban were acidic (pH:2.4 ± 0.6) and mainly governed by non-sea-salt-SO42-. The volume and mass normalized oxidative potential of PM10 was found to be 1.81 ± 0.40 nmol DTT min-1 m-3 and 18.4 ± 6.1 pmol DTT min-1 μg-1 respectively which are surprisingly higher than several urban atmospheres across the world including IGP. The acid-digested water-soluble transition metals (Cu, Mn) show higher influences in the oxidative potential (under high aerosol acidity) compared to the WSOC. The study revealed that the advection of regional solid fuel burning plume and associated non-sea-salt-SO42- is enhancing aerosol acidity and oxidative stress that in turn alters the intrinsic properties of aerosols over such marine ecosystems rich in ecology and bio-geochemistry.

Stochastic processes drive the diversity and composition of methanogenic community in a natural mangrove ecosystem

Methanogens are considered to be crucial components of mangrove ecosystems with ecological significance. However, understanding the assembly processes of methanogenic communities in mangrove ecosystems is relatively insufficient. In the current study, a natural mangrove in a protection zone was employed to investigate the diversity and assembly processes of methanogenic community by using amplicon high-throughput sequencing, a null model as well as a neutral community model. The results showed that methanogenic community in mangrove sediments were highly diverse, with the predominance of methylotrophic Methanolobus, and hydrogenotrophic Methanogenium, Methanospirillum. The diversity, composition, and gene abundance varied obviously across the mangrove sampling sites, whereas the measured environmental variables exhibited a negligible effect. Null model showed that the values of beta nearest-taxon index were mostly between -2 and 2, indicating that stochastic processes contributed more than deterministic processes driving the methanogenic community assembly in mangrove sediments. Neutral community model revealed a high estimated migration rate of methanogenic community, further substantiating the significance of stochastic processes. Among the keystone species identified in network analysis, methanogens affiliated to hydrogenotrophic Methanospirillum may have a crucial role in maintaining the structure and function of methanogenic community. Notably, these keystone species were almost unaffected by measured environmental factors, indicating that the methanogenic community in mangrove sediments is more likely to be affected by stochastic processes. This study deepens the understanding of the diversity and assembly of methanogenic community in mangrove sediments, and provides clues to maintain mangrove ecosystem functioning.

Saving the overlooked mangrove horseshoe crabs-A perspective from enhancing mangrove ecosystem conservation

Despite being widely distributed in Asia, Carcinoscorpius rotundicauda is often overlooked and, its population status remains unclear. Moreover, it is threatened by illegal harvesting and degradation of mangrove ecosystems. Protecting its habitat is essential for population and biodiversity conservation, as mangroves provide nursery grounds and food supply for C. rotundicauda. This review discusses the biological characteristics of C. rotundicauda, including ecology, nutrition, life history, toxicology, and immunology. It also presents information about its distribution and population status. The review emphasizes the challenges faced by C. rotundicauda and proposes a conservation framework that involves the participation of local residents to facilitate conservation efforts. Collaboration between local residents and communities is proposed to protect and monitor the mangrove ecosystem. Additionally, this framework can support field research, protect C. rotundicauda juveniles and other species, and ensure the livelihood of local residents through participation in carbon trading markets and eco-industries such as eco-farming and eco-tourism.

Occurrence and patterns of metals in mangrove forests from the Oman Sea, Iran

Concentrations of selected metals were investigated in roots, stems, leaves and sediments from mangrove forests situated along the coast of the Oman Sea, Iran. Results showed that the overall average concentrations of lead, nickel, copper, and zinc in sediments were 47.90, 54.12, 42.13 and 44 μg/g dry weight (dw) and 3.81, 16.41, 29.23 and 25 μg/g dw in plant tissues, respectively. In addition, the bioconcentration factors (BCFs) of root, stem and leaf ranged from 0.5 to 1.7, 0.2 to 1.5, and 0.4 to 1.3, respectively. Pollution indices showed that all investigated sites were in the category of low to moderate pollution (pollution load index: 1.5-0.11), with a 21 % probability of biological toxicity.

Assessment of heavy metals at mangrove ecosystem, applying multiple approaches using in-situ and remote sensing techniques, Red Sea, Egypt

Mangrove areas are considered the most retention zone for heavy metal pollution as it work as an edge that aggregates land and sea sediments. This study aims to examine if the heavy metals' existence in the mangrove sediment is related to contamination or natural resources. In addition, it gives an interpretation of the origin of these metals along the Egyptian Red Sea coast. Twenty-two samples of mangrove sediments were collected and then, analyzed for metals (Mn, Ni, Cu, Fe, Cd, Ag, and Pb) using inductively coupled plasma mass spectroscopy (ICP-MS). Integration between the in-situ data, contamination indices, and remote sensing and geographical information science (GIS), and multivariate statistical analysis techniques (PCA) were analyzed to assess and clarify the spatial origin of heavy metals in sediment at a regional scale. The average concentration of heavy metals from mangrove sediments were shown to be substantially lower than the referenced value, ranging from moderate to significant except the levels of Ag were very high. The heavy metals concentrations were expected to be naturally origin rather than anthropogenic and that be confirmed by mapping of Red Sea alteration zones spots. These alteration zones are parallel to mangrove sites and rich by several mineralization types including heavy metals that are carried by flooding to the coastline. Remote sensing and GIS techniques successfully contributed to interpreting the pattern of the origin of heavy metals and discharging systems that control the heavy metals concentration along the Red Sea coast.

Model of shrimp pond-mediated spatiotemporal dynamic distribution of antibiotic resistance genes in the mangrove habitat of a subtropical gulf

Aquacultures are the main reason for the environmental selection of antibiotic resistance genes (ARGs), resulting in the enrichment of ARGs. As a filter, a marine mangrove ecosystem can reduce antimicrobial resistance (AMR) or eliminate ARGs; however, its elimination mechanism remains unclear. This study investigated the spatiotemporal dynamic distribution of ARGs in two different types of mangrove habitats (shrimp ponds and virgin forests), within a subtropical gulf located in the Beibu Gulf, China, during dry and wet seasons by using metagenomics and real time quantitative polymerase chain reaction (RT-qPCR) analysis. As the key environmental factors, sulfide, salinity, and mobile genetic elements significantly were found to contribute to ARGs distribution, respectively. Wet and dry seasons influenced the dispersal of ARGs but did not affect the microbial community structure. Three potential biomarkers, TEM-116, smeD, and smeE, played key roles in seasonal differences. The key different genes in the biological relevance of absolute abundance were demonstrated by RT-qPCR. Co-occurrence network analysis indicated that high-abundance ARGs were distributed in a modular manner. For the first time, a risk index weighted by risk rank (RIR) was proposed and used to quantify the human risk of ARGs in the mangrove metagenome. The shrimp ponds during the wet season showed the highest RIR detected. In addition to offering a perspective on reducing AMR in mangrove wetlands, this study constructed the first spatiotemporal dynamic model of ARGs in the Beibu Gulf, China and contributed to revealing the global spread of ARGs. Meanwhile, this study proposes a new pipeline for assessing the risk of ARGs, while also exploring the concept of "One Health."

Extreme rainstorm reshuffles the spatial distribution of heavy metals and pollution risk in sediments along the mangrove tidal flat

Mangroves as typical blue carbon ecosystems exhibit a high level of heavy metal accumulation capability. In this study, we investigated how extreme rainstorm effects the spatial variability and pollution risk of sediment heavy metals (i.e., Fe, Mn, Cr, Cu, Zn, Cd, Pb, As and Hg) at different compartments of a typical tidal flat, including the bare mudflat, mangrove zone, and tidal creek in Shenzhen Bay, China. The results showed that the extreme rainstorm can change the sediment particle size, which further regulated the spatial distribution, and source-sink pattern of heavy metals. Due to the strong rainstorm flushing, the concentrations of most heavy metals increased toward the sea and the comprehensive pollution level increased by 8.3 % after the extreme rainstorm. This study contributes to better understanding of how extreme rainstorm regulates heavy metal behavior in mangrove sediments to achieve sustainable development of mangroves under the pressures of extreme weather events.

The pervasiveness of microplastic contamination in the gastrointestinal tract of fish from the western coast of Bangladesh

This study investigated the prevalence of microplastics (MPs) in the gastrointestinal tract (GIT) of fish from the western coast of Bangladesh, the world's largest mangrove ecosystem. Altogether, 8 different species of fish (5 demersal and 3 pelagic) were examined. Microplastics were detected in every individual fish with an average abundance of 7.1 ± 3.14 particles per specimen. The demersal species were observed to consume more microplastics (7.78 ± 3.51) than the pelagic species (5.92 ± 2.06). Moreover, small-sized fish was found to accumulate higher MPs/body weight than large-sized fish. Polypropylene was the most abundant polymer type (45 %) and fiber was the most prevalent shape (71 %). SEM analysis revealed cracks, pits, and foreign particles on the microplastics' surface, representing their ability to bear organic pollutants and heavy metals. This study will be a source of information for future research and a guide for policy-makers to take better actions to protect and restore marine resources.

Deciphering the biodesulfurization pathway employing marine mangrove Bacillus aryabhattai strain NM1-A2 according to whole genome sequencing and transcriptome analyses

In the biogeochemical cycle, sulfur oxidation plays a vital role and is typically referred to as the elemental sulfur or reductive sulfide oxidation process. This study aimed to characterize a subtropical mangrove-isolated bacterial strain using biochemical, whole-genome, and transcriptome sequencing analyses to enhance our understanding of sulfur metabolism and biodegradation from a molecular genetic perspective. Strain NM1-A2 was characterized as Gram-positive and found to have a close molecular phylogenetic relationship with Bacillus aryabhattai. NM1-A2 efficiently converted dibenzothiophene (DBT) into 2-hydroxybiphenyl (2-HBP) via a 4S pathway with 95% efficiency, using enzymes encoded by the dsz operon (dszA, dszB, and dszC), which determine monooxygenases (DszA & DszC) and desulfinase (DszB). The whole-genome sequence of NM1-A2 had a length of approximately 5,257,678 bp and included 16 sulfur metabolism-related genes, featuring the ABC transport system, small subunit (ssu) and cysteine (cys) gene families, and adenosine 5'-phosphosulfate (APS) and 3'-phosphoadenosine-5'-phosphosulfate (PAPS) biosynthesis-related genes. Transcriptomic analysis of NM1-A2 using three sulfur groups-magnesium sulfate (MS), sulfur powder (SP), and sodium thiosulfate (ST) resulted in a significant number of differentially expressed genes (1200, 2304, and 2001, respectively). This analysis revealed that intracellular cysteine concentration directly regulated the expression of cys and ssu genes. Sulfate did not directly affect cys gene expression but repressed ssu gene expression. The cys gene expression levels decreased during the conversion of sulfate to sulfide and cysteine. The transcriptomic data was validated by analyzing the expression patterns of NM1-A2 using real-time quantitative PCR validation analysis. The expression levels of cysl, mccB, and nrnA were significantly upregulated, while cysH, metB, and sat were downregulated in the SP, ST, and MS groups, respectively. This research contributes to our understanding of marine mangrove microorganisms' bacterial efficiency through characterization, whole-genome, and transcriptome sequencing-based molecular degradation of organic compounds in the mangrove ecosystem, which may enhance nutrient availability.

Environmental magnetic signatures in mangrove ecosystems in northern Persian Gulf: Implication for pollution assessment in marine environment

Magnetic properties of root, bark, and leaf of mangrove (Avicenna marina) and sediment were determined for pollution assessment at three locations in the northern coast of the Persian Gulf. The study revealed that the sources of the particles deposited on leaf surfaces can be discriminated via saturation isothermal remanent magnetization (SIRM) values and heavy metal. However, different factors including wind direction, size of the magnetic particles and crown density, play a role using SIRM for biomonitoring of atmospheric particulate matter. For leaves, the significant correlations between SIRM and leaf elemental contents indicated that the deposited particles on their surface mainly have geogenic sources. The magnetic analyses revealed that leaves are more suitable than bark for monitoring atmospheric pollution using mangrove trees due to the effect of different factors including dense crown of trees, washing of tree trunk by sea waves, and elements translocation from roots and sediments. Instead, the positive and significant correlation between the SIRM values for sediments and mangrove roots, and no or negative correlation between sediments and roots with barks and leaves indicates that the magnetic properties of the sediments and mangrove roots are suitable indicators of pollution in aquatic environment.

Climate and nutrients regulate biographical patterns and health risks of antibiotic resistance genes in mangrove environment

Mangroves are prone to receive pollutants and act as a sink for antibiotic resistance genes (ARGs). However, knowledge of the human health risk of ARGs and its influencing factors in mangrove ecosystems is limited, particularly at large scales. Here, we applied a high-throughput sequencing technique combined with an ARG risk assessment framework to investigate the profiles of ARGs and their public health risks from mangrove wetlands across South China. We detected 456 ARG subtypes, and found 71 of them were identified as high-risk ARGs, accounting for 0.25 % of the total ARG abundance. Both ARGs and bacterial communities showed a distance-decay biogeography, but ARGs had a steeper slope. Linear regression analysis between features of co-occurrence network and high-risk ARG abundance implies that greater connections in the network would result in higher health risk. Structural equation models showed that geographic distance and MGEs were the most influential factors that affected ARG patterns, ARGs and MGEs contributed the most to the health risk profiles in mangrove ecosystems. This work provides a novel understanding of biogeographic patterns and health risk assessment of ARGs in mangrove ecosystems and can have profound significance for mangrove environment management with regard to ARG risk control.

Temperature drives the assembly of Bacillus community in mangrove ecosystem

Mangroves are located at the interface of terrestrial and marine environments, and experience fluctuating conditions, creating a need to better explore the relative role of the bacterial community. Bacillus has been reported to be the dominant group in the mangrove ecosystem and plays a key role in maintaining the biodiversity and function of the mangrove ecosystem. However, studies on bacterial and Bacillus community across four seasons in the mangrove ecosystem are scarce. Here, we employed seasonal large-scale sediment samples collected from the mangrove ecosystem in southeastern China and utilized 16S rRNA gene amplicon sequencing to reveal bacterial and Bacillus community structure changes across seasons. Compared with the whole bacterial community, we found that Bacillus community was greatly affected by season (temperature) rather than site. The key factors, NO₃-N and NH₄-N showed opposite interaction with superabundant taxa Bacillus taxa (SAT) and three rare Bacillus taxa including high rare taxa (HRT), moderate rare taxa (MRT) and low rare taxa (LRT). Network analysis suggested the co-occurrence of Bacillus community and Bacillus-bacteria, and revealed SAT had closer relationship compared with rare Bacillus taxa. HRT might act crucial response during the temperature decreasing process across seasons. This study fills a gap in addressing the assembly of Bacillus community and their role in maintaining microbial diversity and function in mangrove ecosystem.

Urban mangrove ecosystems are under severe threat from microplastic pollution: a case study from Mangalavanam, Kerala, India

The prevalence of microplastics in urban mangrove ecosystems has received little scientific attention despite their immense ecological significance. An investigation was conducted to assess the microplastic abundance and characteristics in three different environmental compartments viz; soil (933 ± 564 particles/kg), sediment (1275 ± 532 particles/kg d.w.), and water (101.6 ± 24 particles/liter) of the Mangalavanam bird sanctuary, a protected mangrove forest in the Cochin city of India. Microplastic fibres were predominant in water, while soil and sediment contained a higher proportion of microplastic fragments. Importantly, surrounding urban features and tidal fluctuation were considered to be influencing microplastic metrics in the area. The colour composition of microplastics was found to be similar in all three environmental compartments and most of the identified polymers were those which are scarcely recycled. Altogether, this study highlights the importance of adopting location-specific measures to protect the area from microplastic pollution and provides the baseline data required for further assessing the impacts of microplastic pollution on mangroves, avifauna, and other components of biodiversity in the region.

Elucidating the surface macroplastic load, types and distribution in mangrove areas around Cebu Island, Philippines and its policy implications

The Philippines is identified as one of the major marine plastic litter polluters in the world with a discharge of approximately 0.75 million tons of marine plastic debris per year. However, the extent of the plastic problem is yet to be defined systematically because of limited research. Thus, this study aims to quantify plastic litter occurrence in mangrove areas as they function as sinks for plastic litter due to their inherent nature of trapping plastics. To define the extent of marine plastic pollution on an island scale, mangrove areas in 14 municipalities around Cebu Island were sampled, with 3 to 9 transects in each site depending on the length of coastline covered by mangroves. Sampling and characterization of both plastics and the mangrove ecosystem was performed in three locations along the transect - landward, middle, and seaward. A total of 4501 plastic items were sampled throughout the study sites with an average of 1.29 ± 0.67 items/m² (18.07 ± 8.79 g/m²). The average distribution of plastic loads were 2.68 ± 1.9 items/m² (38.52 ± 25.35 g/m²), 0.27 ± 0.10 items/m² (6.65 ± 4.67 g/m²), and 0.94 ± 0.61 items/m² (9.04 ± 4.28 g/m²) for the landward, middle, and seaward locations, respectively. The most frequent plastic types found were i) packaging, ii) plastic bags and iii) plastic fragments. The plastic loads and types suggest that most plastic wastes trapped in mangroves come from the nearby communities. Fishing-related plastics originated from the sea and were transported across the mangrove breadth. The findings confirm that mangroves are major traps of plastic litter that might adversely affect the marine ecosystem. The study underscores the urgent need for waste mitigation measures, including education, community engagement, infrastructure, technological solutions and supporting policies.

Linking human activity to spatial accumulation of microplastics along mangrove coasts

Microplastics (MP) in mangrove coasts are threating ecological health and seafood safety. However, quantitative evidence on the effects of different coastal human activities on microplastic accumulation in mangrove sediments is lacking, thereby impeding the policy development of evidence-based waste management. In this study, continuous geographical sampling (N = 50) was applied to collect sediments from the largest mangrove coast, namely the Leizhou Peninsula in China. Similar worldwide research data (16 mangrove coasts) were collected from the Science Citation Index Expanded (SCIE) database of the Web of Science. The connections between human drivers and microplastic accumulation were evaluated by spatial comparison, multi-correspondence analysis, and multiple differences analysis. The microplastic abundance fluctuated widely along the mangrove coasts (average value was 51.24, ranged from 6.40 to 255.57 items·kg^-1 dry weight; coefficient of variation = 97%) with a globally lower-middle concentration in sediments of the Leizhou Peninsula. Densely populated urban residents and the floating population of tourists largely contributed to the high abundance of microplastics in mangrove sediments, of which large-sized (1-5 mm) white foams were the dominant type. Although suburbs had less crowds, both onshore and offshore fishery production could cause high accumulation of microplastics in neighboring mangrove coasts, which were characterized by small-sized (<1 mm) fragments with fresh color. Small microplastics (80%) with fresh color (44%) were dominant. Weathering may break down more toxic particles in urban areas neighboring mangrove coasts. Larger mangrove patches could partly block ocean-based microplastics; however, coasts surrounded by more geographical barriers had intensified pollutant accumulation. It was suggested that foam packaging of commodities for urban residents and tourists in popular tourism areas should be reduced and restrictions of fishery waste plastics are needed along shores with mangroves, especially in coasts surrounded by more geographic barriers.

Iron and phosphorus geochemistry in the core sediments of an urbanized mangrove ecosystem, Southwest coast of India

This study has been carried out to understand the geochemistry of elements namely, iron (Fe) and phosphorus (P) in the core sediments of an urbanized tropical mangrove ecosystem along the Southwest coast of India. The study revealed the coupling of iron and phosphorus in which the reductive conditions induced reductive dissolution and upward transport of Fe, causing surface coprecipitation of phosphorus incorporated Fe oxyhydroxides. The accumulation and transformation of phosphorus were significantly influenced by processes viz., phosphorus regeneration due to organic matter mineralization and adsorption to inorganic iron oxides/Ca bound minerals in the surface sediments, and phosphorus retention in the sedimentary column by transformation into refractory organic phosphates. Bioavailable phosphorus (BAP) accounted for more than 50% of TP, so that the mangrove sediments act as an important internal nutrient source of iron and phosphorus for coastal eutrophication.

Effect of land-use and land-cover change on mangrove soil carbon fraction and metal pollution risk in Zhangjiang Estuary, China

Land-use and land-cover change (LULCC) is the main cause of mangrove deforestation and degradation. However, the effect of LULCC on mangrove soil organic carbon (SOC) fractions and metal pollution risks, and the difference between the effects of those two soil evolutions are largely unknown. Here, we collected soil samples from natural systems (mangroves and mudflat), land-cover changes (Spartina alterniflora invasion), and anthropogenic land-use changes (cropland and culture pond) in Zhangjiang Estuary. We determined the soil aggregate fractions (macro-aggregate, micro-aggregate, and silt-clay fraction) and the associated carbon, and heavy metal dynamics. Our findings suggested that LULCC did not remarkably affect SOC contents, but changed the soil aggregate structures. LULCC significantly increased aggregate-associated carbon fractions, especially macro-aggregate carbon fraction. The large proportion of silt-clay fraction in natural systems was corresponding to a high percentage of mineral organic carbon, indicating that LULCC decreases the mangrove SOC stability. Land-cover change promoted the accumulation of SOC, nitrogen, and heavy metals compared with uninvaded mudflat. The heavy metal contents in mangrove soil were highest among all studied soils, expect for Cd, which suggested that mangrove soil had high metal accumulation. However, land-use changes could stimulate the mobility and dynamics of metals enriched in mangrove soils; these changes, especially in cropland, will also cause a large amount of exogenous Cd being exported into the adjacent aquatic environment. Thus, mangrove shifts metal pollutant from sink to source when affected by land-use changes. The contamination index demonstrated that heavy metals have posed ecological risks, especially for Cd in cropland. Compared with mangrove, land-use change was dominated by single-element pollution, but land-cover change showed low multiple-element complex pollution. These findings elucidate the effects of LULCC on mangrove SOC fraction and metal pollution risk, and are of great significance for designing the long-term management and conservation policies for mangrove managers.

Trace metal distribution and ecological risk assessment in the core sediments of a highly urbanized tropical mangrove ecosystem, Southwest coast of India

Distribution and ecological risk assessment of trace metals were carried out in the core sediments of a highly urbanized tropical mangrove ecosystem along the Southwest coast of India. The metal distribution pattern was as follows: Co, Cu, Ni and Pb adsorbed onto Fe oxyhydroxides and fine grained sediments; Cd and Zn preferential adsorption by organic matter and Cr scavenging by Mn oxyhydroxides. Cd, Pb and Zn were significantly enriched in upper sediments, while Cd, Ni and Zn were present in metal exchangeable fractions. Geoaccumulation index (I_geo) suggested that the study area showed moderate to strong pollution of Cd and Zn, whereas unpolluted to moderately polluted with respect to Co, Cr, Cu, Mn, Ni and Pb. Cd enrichment caused high ecological risk, primarily attributed to anthropogenic activities. Mangrove ecosystems are efficient sequester of trace metals but anthropogenic addition can cause significant fraction of exchangeable metals and pose high ecological risk.

Unique functional responses of fungal communities to various environments in the mangroves of the Maowei Sea in Guangxi, China

Fungi are important compartments of microbial communities of mangroves. Their diversity might be influenced by their habitat environment. This study analyzed the distribution and function of fungal communities in the sediments and plant samples from mangrove ecosystem of the Maowei Sea area in Guangxi, China. The results showed that phytopathogenic fungi Cladosporium (17.00%) was mainly observed in the sediments from the protected zone, while endophytic fungi Alternaria (9.22%) and Acremonium (6.09%) were only observed in the sediments from wharf. The fungi in the sediments from village and park were mainly consisted of high-activity endophytes and fungi related to lignin-degrading, respectively. Acaulospora and Aspergillus with higher relative abundance discovered in plant tissues could help plant growth. Cirrenalia (37.66%) and Lignincola (26.73%) with high-activity for lignin-degrading were discovered in decayed leaves. The distribution and function of fungi were highly dependent on the environment settings, thus the fungi can be used as indicators for monitoring the environmental change of mangrove ecosystems.

Plant hosts may influence arbuscular mycorrhizal fungal community composition in mangrove estuaries

We investigated the role of plant host and soil variables in determining arbuscular mycorrhizal fungi (AMF) community composition in plant roots of two spatially separated mangrove estuaries on the rivers Aghanashini (14° 30' 30″ N-74° 22' 44″ E) and Gangavali (14° 35' 26″ N-74° 17' 51″ E) on the west coast of India. Both mangrove estuaries had similar plant species composition but differed in soil chemistries.We amplified a 550-bp portion of 18S small subunit (SSU) rDNA from mangrove plant roots and analysed it by restriction fragment length polymorphism (RFLP). Clones representing unique RFLP patterns were sequenced. A total of 736 clones were obtained from roots of seven and five plant species sampled at Aghanashini and Gangavali, respectively. AMF phylotype numbers in plant roots at Aghanashini (12) were higher than at Gangavali (9) indicating quantitative differences in the AMF community composition in plant roots at the two mangrove estuaries. Because both estuaries had similar plant species composition, the quantitative difference in AMF communities between the estuaries could be an attribute of the differences in rhizospheric chemistry between the two sites.Non-metric multidimensional scaling (NMDS) revealed overlap in the AMF communities of the two sites. Three and two AMF phylotypes had significant indicator value indices with specific hosts at Aghanashini and Gangavali, respectively. Environmental vector fitting to NMDS ordination did not reveal a significant effect of any soil variable on AMF composition at the two sites. However, significant effects of both plant hosts and sites were observed on rhizospheric P. Our results indicate that root AMF community composition may be an outcome of plant response to rhizospheric variables. This suggests that plant identity may have a primary role in shaping AMF communities in mangroves.

nov., isolated from mangrove ecosystem

Three Gram-staining negative, facultatively anaerobic, rod-shaped and motile strains, FJAT-51800^T, FJAT-52962^T and FJAT-54481^T were isolated from the sediment samples of Zhangjiang Estuary Mangrove National Nature Reserve in Fujian Province, China. The 16S rRNA gene sequencing results indicated they could be novel members of the genus Shewanella. The optimum temperature for growth was 30 °C. The respiratory quinones of the strains were ubiquinone Q-7 or Q-8, and menaquinone MK-7. Polar lipids of the strains FJAT-52962^T and FJAT-51800^T were phosphatidyl glycerol, phosphatidyl ethanolamine, and unidentified aminophospholipids while strain FJAT-54481 consist of phosphatidylglycerol, phosphatidylethanolamine, unidentified aminophospholipids, two unidentified aminolipids and four unidentified lipids. The major fatty acid of the three strains was iso-C_15:0. The genomic DNA G + C contents of strains FJAT-51800^T, FJAT-52962^T and FJAT-54481^T were 48.2, 55.3 and 48.1%, respectively. The average nucleotide identity and digital DNA-DNA hybridization values between strains FJAT-51800^T, FJAT-52962^T and FJAT-54481^T and other closely related Shewanella members were below the cut-off level (95-96%) for species identification. Genome analysis showed that these strains encode genes for osmo-regulation. Based on the results of phenotypic, chemotaxonomic and genome analyses, strains FJAT-51800^T, FJAT-52962^T and FJAT-54481^T represent three novel species of the genus Shewanella, for which the names Shewanella avicenniae sp. nov., Shewanella sedimentimangrovi sp. nov., and Shewanella yunxiaonensis sp. nov., are proposed. The type strains are FJAT-51800^T (= GDMCC 1.2204^T = KCTC 82448^T), FJAT-52962^T (= MCCC 1K05496^T = KCTC 82445^T) and FJAT-54481^T (= GDMCC 1.2348^T = KCTC 82646^T).

Microbially-driven sulfur cycling microbial communities in different mangrove sediments

Microbially-driven sulfur cycling is a vital biogeochemical process in the sulfur-rich mangrove ecosystem. It is critical to evaluate the potential impact of sulfur transformation in mangrove ecosystems. To reveal the diversity, composition, and structure of sulfur-oxidizing bacteria (SOB) and sulfate-reducing bacteria (SRB) and underlying mechanisms, we analyzed the physicochemical properties and sediment microbial communities from an introduced mangrove species (Sonneratia apetala), a native mangrove species (Kandelia obovata) and the mudflat in Hanjiang River Estuary in Guangdong (23.27°N, 116.52°E), China. The results indicated that SOB was dominated by autotrophic Thiohalophilus and chemoautotrophy Chromatium in S. apetala and K. obovata, respectively, while Desulfatibacillum was the dominant genus of SRB in K. obovata sediments. Also, the redundancy analysis indicated that temperature, redox potential (ORP), and SO₄^2- were the significant factors influencing the sulfur cycling microbial communities with elemental sulfur (ES) as the key factor driver for SOB and total carbon (TC) for SRB in mangrove sediments. Additionally, the morphological transformation of ES, acid volatile sulfide (AVS) and SO₄^2- explained the variation of sulfur cycling microbial communities under sulfur-rich conditions, and we found mangrove species-specific dominant Thiohalobacter, Chromatium and Desulfatibacillum, which could well use ES and SO₄^2-, thus promoting the sulfur cycling in mangrove sediments. Meanwhile, the change of nutrient substances (TN, TC) explained why SOB were more susceptible to environmental changes than SRB. Sulfate reducing bacteria produces sulfide in anoxic sediments at depth that then migrate upward, toward fewer reducing conditions, where it's oxidized by sulfur oxidizing bacteria. This study indicates the high ability of SOB and SRB in ES, SO₄^2-_,S₂^- and S^2- generation and transformation in sulfur-rich mangrove ecosystems, and provides novel insights into sulfur cycling in other wetland ecosystems from a microbial perspective.

Desulfobacterales stimulates nitrate reduction in the mangrove ecosystem of a subtropical gulf

The amount of nitrogen compounds discharged into the natural environment has increased drastically due to frequent human activities and led to worsening pollution. The mangrove ecosystem can remove nitrogen pollution, in this regard, few studies had focused on the relationship among nitrogen cycling genes, environmental factors, and taxonomic composition. In this study, shotgun metagenomic sequencing and quantitative polymerase chain reaction were used to understand the nitrogen cycle in the subtropical mangrove ecosystem in the Beibu Gulf of China. Eight nitrogen cycling pathways were annotated. Nitrogen metabolism activities were significantly higher in the wet season than those in the dry season. The most abundant genes were those related to the synthesis and degradation of organic nitrogen, followed by the genes involved in nitrate reduction (denitrification, dissimilation/assimilation nitrate reduction). Furthermore, dissimilation nitrate reduction was the main nitrate reduction pathway. Desulfobacterales plays an important role in nitrogen cycling and contributes 12% of the genes of nitrogen pathways on average; as such, a strong coupling relationship exists among nitrogen cycling, sulfur cycling, and carbon cycling in the mangrove ecosystem. Nitrogen pollution in the mangrove wetland can be efficiently alleviated by nitrate reduction of Desulfobacterales. Nevertheless, only 50% of genes can be matched among the known species, suggesting that many unknown microorganisms in the mangrove ecosystem can perform nitrogen cycling. Total phosphorus, available iron, and total organic carbon are the key environmental factors that influence the distribution of nitrogen cycling genes, related pathways, and the taxonomic composition. Our study clearly illustrates how the mangrove ecosystem mitigates nitrogen pollution through Desulfobacterales. This finding could provide a research reference for the whole nitrogen cycling in the mangrove ecosystem.

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.

Temperature and salinity drive comammox community composition in mangrove ecosystems across southeastern China

Complete ammonia-oxidizing (comammox) microorganisms are newly recognized nitrifying bacteria found in natural and engineered ecosystems. Mangrove ecosystems are hotspots for nitrogen cycling, but the knowledge of comammox diversity and abundance, and particularly, driving factors, in these ecosystems is scarce. We here used deep sequencing to investigate comammox diversity in six mangrove ecosystems across southeastern China. Our results showed that comammox microorganisms in mangrove sediments were extremely diverse. Phylogenetic analysis revealed a novel comammox group within clade A that formed a distinct cluster for which no reference sequence existed, implying their potential uniqueness. Quantitative PCR demonstrated that comammox abundance was slightly higher than that of the canonical ammonia-oxidizing bacteria but significantly lower than that of ammonia-oxidizing archaea, indicating they are not the dominant ammonia oxidizers in mangrove ecosystems. Finally, variation partition analysis revealed a significant decrease in similarity of comammox communities along the geographical distance, and a pronounced effect of the geographic factors and sediment attributes on the composition of comammox microorganisms and the abundance variations of ammonia oxidizers. Temperature and salinity were the most important contributing factors that shaped the comammox community. Further, detection of diverse comammox microorganisms in extremely high-salinity sediments suggested that this community could adapt to high salinity environments, which indicates salinity may not be a critical factor resulting in the absence of comammox microorganisms in open-ocean environments. This study expanded the current understanding of the diversity and niche preference of comammox in mangrove ecosystems, and further enhanced our understanding of adaptation potential of comammox communities.

Prevalence of microplastic contamination in the digestive tract of fishes from mangrove ecosystem in Cispata, Colombian Caribbean

Plastics in Colombian marine-coastal ecosystems are being fragmented by various environmental factors, generating microplastics (size < 5 mm), an emerging pollutant that is ingested by marine organisms, representing a threat to ecosystems and potentially also to humans. This study aims to evaluate the incidence of microplastic ingestion by fishes from mangrove ecosystems in Cispata, Colombian Caribbean. The digestive tract content of 302 specimens of 22 fish species were analyzed using the KOH digestion method (500 g/5 L), stereoscopic visual identification and infrared spectroscopy. A total of 69 microplastics were found in the digestive tract of 7% of the analyzed fishes. 55% of the ingested microplastics were filaments, 23% fragments, 19% films, and 3% foam. The results of this study raised concerns about microplastic contamination in the marine environments, a threat to the fishery resource and to public health, which requires actions to prevent and reduce its negative effects.

Small microplastic particles (S-MPPs) in sediments of mangrove ecosystem on the northern coast of the Persian Gulf

We present a study of small microplastic particles (S-MPPs) in the sediments of mangrove ecosystem of Khor-e- Khoran, a Ramsar site in Iran. The spatial distribution of S-MPPs (<1 mm) in mangrove surface sediments were investigated, which provided new insights into the detection and composition of S-MPPs in the study area. S-MPPs were extracted via the air-induced overflow (AIO) extraction procedure, and then they were counted and categorized according to the particle shape, color and size. The mean number of S-MPPs at the five sampling sites ranged from 19.5 to 34.5 particles per kg dry sediment in Bandar Gelkan and Bandar Lengeh, respectively. In general, microfibres followed by fragments were the most common type of S-MPPs isolated in each site (>56% and ~35%, respectively). Sewage discharge is probably the main source of extracted fibres in almost all the sites. The observed S-MPPs were classified into two size groups (10-300 μm and 300-1000 μm). The majority of S-MPPs fell into the smallest size group which accounted for 70-97% of the total S-MPPs. Fourier transform infrared (FTIR) analysis of some subsamples showed that polyethylene (PE) was the most common recovered polymer. Some non-plastic particles were also isolated from plastic-like particles of suspected S-MPPs in the mangrove sediments using a Scanning Electron Microscope (FE-SEM). This study provided the first evidence of S-MPPs contamination in the mangroves of the Iranian coast of the Persian Gulf. Long-term studies are required to understand, monitor and prevent further microplastics pollution in the region.

Organochlorine concentrations in aquatic organisms from different trophic levels of the Sundarbans mangrove ecosystem and their implications for human consumption

The Sundarbans, a highly biodiverse tropical ecosystem stretching across India and Bangladesh, is also the largest mangrove forest in the world. Organochlorine compounds (OCs) have been extensively used for agriculture and sanitary purposes in the region. OCs can accumulate in biological tissues and biomagnify in organisms through food webs, for which reason they reach high concentrations in top predators. Because marine food webs are long and marine predators are extensively used in the region as human food, assessment of potential health-related risks caused by OC pollution is in order. This study is the first to determine the concentration of PCBs in fish and crustaceans from the Sundarbans mangroves, their accumulation trends through the food web, and the potential toxicological risk that their consumption poses to humans. DDT concentrations, which had already been assessed in the region, were also determined. The median concentrations ranged from below detection limits to 176.3 ng g^-1 lipid weight for tDDT and 275.9  ng g^-1 for PCBs. Overall, these concentrations were lower than those usually observed in other regions of the world, apparently as a result of the interplay of several factors: low environmental organochlorine inputs, the physical and climatic characteristics of an ecosystem dominated by high temperatures in a highly flushed ecosystem that dilutes and rapidly disperses pollutants, and the comparatively short food chain lengths that, similarly to other mangrove ecosystems, characterize the Sundarbans. Organochlorine concentrations were 2-3 orders of magnitude lower than commonly accepted tolerance levels, so their consumption do not pose a sensible risk to the population. However, concentrations of DDT in dry fish from retail markets were higher because this compound is used for pest control during fish processing. Potential risks involved in this practice likely outweigh potential benefits, so it is recommended that this compound is substituted by less hazardous alternatives.

Marine litter and microplastic pollution on mangrove soils of the Ciénaga Grande de Santa Marta, Colombian Caribbean

Marine litter pollution has become a complex global problem, because of the negative ecological and socioeconomic impacts as well as the human health risks that it represents. In Colombia, mangroves are affected by inadequate solid waste management, which results in litter accumulation. Additionally, the information related to this problem is limited avoiding the development of prevention and reduction strategies. For the first time, pollution by marine litter and microplastics were evaluated in mangrove soils of the Ciénaga Grande de Santa Marta, where 540 ± 137 and 31 ± 23 items/ha of marine litter were determined in mangroves near and away from populated centers respectively. Plastics represented between 73 and 96% of litter, and microplastic quantity oscillated between 31 and 2,863 items/kg finding the highest concentrations in mangroves near to the population. This study contributes to the knowledge of the marine litter problem in mangroves of the Colombian Caribbean, becoming a help for their conservation.

Interactions of sulfur and methane-oxidizing bacteria in tropical estuarine sediments

The bacterial oxidation of sulfur and methane is central to the biogeochemical processes in sediments such as the tropical mangrove sediments. However, there is a lacuna of information on the seasonal interactions including the influence of monsoons which is a major driver of seasonal change, on sulfur-oxidizing bacteria (SOB) and methane-oxidizing bacteria (MOB), their activity and the environmental variables. To understand these interactions, the analysis was carried out on sediment samples that were sampled monthly for a year from Chorao mangrove, Goa, southwest coast of India. SOB (3.8×10⁵CFU g^-1) and MOB (0.90×10⁵CFU g^-1) had maximum average abundance in the surface sediments in the post-monsoon and monsoon season, respectively. The mean sulfur-oxidation activity (SOA) of 2.63 mM day^-1 and methane-oxidation activity (MOA) of 110.94 mM day^-1 were highest in surface sediments during the post-monsoon season. Generally, the activity of SOB and MOB in surface sediments of post-monsoon was 2.2 times(×) and 2.8× respectively higher than that in the monsoon season. Among the environmental parameters analyzed, protein and sulfide concentrations significantly (p < 0.001) influenced SOA and MOA, respectively. There was a significant difference in SOA (p < 0.003) and MOA (p < 0.036) in surface sediments between the monsoon and the post-monsoon season. During the monsoon season, when the system is a sink of terrestrial/anthropogenic material, the interrelationship of SOB with MOA (r = 0.617, p < 0.001) and SOB with SOA (r = 0.489, p < 0.05) aids in maintaining the homeostasis of the system.

Mangrove Sediment Microbiome: Adaptive Microbial Assemblages and Their Routed Biogeochemical Processes in Yunxiao Mangrove National Nature Reserve, China

Microorganisms play important roles in mangrove ecosystems. However, we know little about the ecological implications of mangrove microbiomes for high productivity and the efficient circulation of elements in mangrove ecosystems. Here, we focused on mangrove sediments located at the Yunxiao National Mangrove Reserve in southeast China, uncovering the mangrove microbiome using the 16S rRNA gene and shotgun metagenome sequencing approaches. Physicochemical assays characterized the Yunxiao mangrove sediments as carbon (C)-rich, sulfur (S)-rich, and nitrogen (N)-limited environment. Then phylogenetic analysis profiling a distinctive microbiome with an unexpected high frequency of Chloroflexi and Nitrospirae appeared to be an adaptive characteristic of microbial structure in S-rich habitat. Metagenome sequencing analysis revealed that the metabolic pathways of N and S cycling at the community-level were routed through ammonification and dissimilatory nitrate reduction to ammonium for N conservation in this N-limited habitat, and dissimilatory sulfate reduction along with polysulfide formation for generating bioavailable S resource avoiding the biotoxicity of sulfide in mangrove sediments. In addition, methane metabolism acted as a bridge to connect C cycling to N and S cycling. Further identification of possible biogeochemical linkers suggested Syntrophobacter, Sulfurovum, Nitrospira, and Anaerolinea potentially drive the coupling of C, N, and S cycling. These results highlighting the adaptive routed metabolism flow, a previously undescribed property of mangrove sediment microbiome, appears to be a defining characteristic of this habitat and may significantly contribute to the high productivity of mangrove ecosystems, which could be used as indicators for the health and biodiversity of mangrove ecosystems.

Bioactive compounds from mangrove derived rare actinobacterium Saccharomonospora oceani VJDS-3

A rare actinobacterium was isolated from Nizampatnam mangrove ecosystem of Andhra Pradesh, India, and was screened for its ability to produce bioactive compounds. The potential strain was identified as Saccharomonospora oceani VJDS-3 by polyphasic taxonomy. Purification of the biologically active compounds by column chromatography led to the isolation of three compounds, namely methoxy ethyl cinnamate (ethyl(E)-3-(4-methoxyphenyl)acrylate) (R1), 4-hydroxy methyl cinnamate (methyl(E)-3-(4-hydroxyphenyl)acrylate) (R2) and 4-methylbenzoic acid (R3). The structure of the compounds was elucidated on the basis of spectroscopic analysis including FTIR, EIMS, 1HNMR and 13CNMR spectroscopies. The antimicrobial activity of the bioactive compounds produced by the strain was tested against a panel of bacteria and fungi, and expressed in terms of minimum inhibitory concentration. Compound (R1) exhibited higher antimicrobial potential (50 µg/ml) against Staphylococcus aureus, Bacillus megaterium and Candida albicans compared to R2 and R3. Antioxidant activity of compounds was determined by DPPH and ABTS radical scavenging activities. The results revealed that compound R3 effectively scavenged DPPH (73.08 ± 1.29) and ABTS (99.74 ± 0.00) radicals at a concentration of 25 and 50 µg/ml, respectively. Antidiabetic and anti-obesity activities were evaluated by inhibitory potential of compounds against alpha-glucosidase, alpha-amylase and pancreatic lipase by spectrophotometric assays. Compound R1 showed effective inhibition against alpha-glucosidase (66.8 ± 1.2) at 20 µg/ml while moderate to weak activities were found against alpha-amylase and pancreatic lipase. To the best of our knowledge, this is the first report on the isolation of supra said compounds from the genus Saccharomonospora.

Larvicidal potency of marine actinobacteria isolated from mangrove environment against Aedes aegypti and Anopheles stephensi

The marine soil samples were collected from different locations of Parangipettai mangrove ecosystem, Vellar estuary, southeast coast of India. Totally 30 different marine actinobacteria were isolated by serial dilution plate technique on starch casein agar medium. The isolated actinobacteria were investigated for their larvicidal activity against Aedes aegypti and Anopheles stephensi mosquitoes. Streptomyces fungicidicus, S. griseus, S. albus, S. alboflavus and S. rochei were identified as potential biocide producers. Based on the antimicrobial activity, five strains were chosen for larvicidal and pupicidal activity. Among the crude extracts tested, the S. alboflavus extract showed significant activity against Ae. aegypti (LC₅₀ 1.48 ± 0.09 and LC₉₀ 3.33 ± 0.22) and An. stephensi (LC₅₀ 1.30 ± 0.09 and LC₉₀ 3.13 ± 0.21). Five isolates have shown a most significant mortality rate of the Ae. aegypti and An. stephensi mosquito larvae. This is an ideal eco-friendly approach for the control of Japanese encephalitis vectors, Ae. aegypti and malarial vector An. stephensi.

Microbial cellulases - Diversity & biotechnology with reference to mangrove environment: A review

Cellulose is an abundant natural biopolymer on earth, found as a major constituent of plant cell wall in lignocellulosic form. Unlike other compounds cellulose is not easily soluble in water hence enzymatic conversion of cellulose has become a key technology for biodegradation of lignocellulosic materials. Microorganisms such as aerobic bacteria, fungi, yeast and actinomycetes produce cellulase that degrade cellulose by hydrolysing the β-1, 4-glycosidic linkages of cellulose. In contrast to aerobic bacteria, anaerobic bacteria lack the ability to effectively penetrate into the cellulosic material which leads to the development of complexed cellulase systems called cellulosome. Among the different environments, the sediments of mangrove forests are suitable for exploring cellulose degrading microorganisms because of continuous input of cellulosic carbon in the form of litter which then acts as a substrate for decomposition by microbe. Understanding the importance of cellulase, the present article overviews the diversity of cellulolytic microbes from different mangrove environments around the world. The molecular mechanism related to cellulase gene regulation, expression and various biotechnological application of cellulase is also discussed.

Phosphate solubilization and acid phosphatase activity of Serratia sp. isolated from mangrove soil of Mahanadi river delta, Odisha, India

Phosphorus is an essential element for all life forms. Phosphate solubilizing bacteria are capable of converting phosphate into a bioavailable form through solubilization and mineralization processes. Hence in the present study a phosphate solubilizing bacterium, PSB-37, was isolated from mangrove soil of the Mahanadi river delta using NBRIP-agar and NBRIP-BPB broth containing tricalcium phosphate as the phosphate source. Based on phenotypic and molecular characterization, the strain was identified as Serratia sp. The maximum phosphate solubilizing activity of the strain was determined to be 44.84 μg/ml, accompanied by a decrease in pH of the growth medium from 7.0 to 3.15. During phosphate solubilization, various organic acids, such as malic acid (237 mg/l), lactic acid (599.5 mg/l) and acetic acid (5.0 mg/l) were also detected in the broth culture through HPLC analysis. Acid phosphatase activity was determined by performing p-nitrophenyl phosphate assay (pNPP) of the bacterial broth culture. Optimum acid phosphatase activity was observed at 48 h of incubation (76.808 U/ml), temperature of 45 °C (77.87 U/ml), an agitation rate of 100 rpm (80.40 U/ml), pH 5.0 (80.66 U/ml) and with glucose as a original carbon source (80.6 U/ml) and ammonium sulphate as a original nitrogen source (80.92 U/ml). Characterization of the partially purified acid phosphatase showed maximum activity at pH 5.0 (85.6 U/ml), temperature of 45 °C (97.87 U/ml) and substrate concentration of 2.5 mg/ml (92.7 U/ml). Hence the present phosphate solubilizing and acid phosphatase production activity of the bacterium may have probable use for future industrial, agricultural and biotechnological application.

Insights into bacterioplankton community structure from Sundarbans mangrove ecoregion using Sanger and Illumina MiSeq sequencing approaches: A comparative analysis

Next generation sequencing using platforms such as Illumina MiSeq provides a deeper insight into the structure and function of bacterioplankton communities in coastal ecosystems compared to traditional molecular techniques such as clone library approach which incorporates Sanger sequencing. In this study, structure of bacterioplankton communities was investigated from two stations of Sundarbans mangrove ecoregion using both Sanger and Illumina MiSeq sequencing approaches. The Illumina MiSeq data is available under the BioProject ID PRJNA35180 and Sanger sequencing data under accession numbers KX014101-KX014140 (Stn1) and KX014372-KX014410 (Stn3). Proteobacteria-, Firmicutes- and Bacteroidetes-like sequences retrieved from both approaches appeared to be abundant in the studied ecosystem. The Illumina MiSeq data (2.1 GB) provided a deeper insight into the structure of bacterioplankton communities and revealed the presence of bacterial phyla such as Actinobacteria, Cyanobacteria, Tenericutes, Verrucomicrobia which were not recovered based on Sanger sequencing. A comparative analysis of bacterioplankton communities from both stations highlighted the presence of genera that appear in both stations and genera that occur exclusively in either station. However, both the Sanger sequencing and Illumina MiSeq data were coherent at broader taxonomic levels. Pseudomonas, Devosia, Hyphomonas and Erythrobacter-like sequences were the abundant bacterial genera found in the studied ecosystem. Both the sequencing methods showed broad coherence although as expected the Illumina MiSeq data helped identify rarer bacterioplankton groups and also showed the presence of unassigned OTUs indicating possible presence of novel bacterioplankton from the studied mangrove ecosystem.

Alteration of extracellular enzyme activity and microbial abundance by biochar addition: Implication for carbon sequestration in subtropical mangrove sediment

Biochar has attracted more and more attention due to its essential role in adsorbing pollutants, improving soil fertility, and modifying greenhouse gas emission. However, the influences of biochar on extracellular enzyme activity and microbial abundance are still lack and debatable. Currently, there is no information about the impact of biochar on the function of mangrove ecosystems. Therefore, we explored the effects of biochar on extracellular enzyme activity and microbial abundance in subtropical mangrove sediment, and further estimated the contribution of biochar to C sequestration. In this study, sediments were amended with 0 (control), 0.5, 1.0 and 2.0% of biochar and incubated at 25 °C for 90 days. After incubation, enzyme activities, microbial abundance and the increased percentage of sediment organic C content were determined. Both increase (phenol oxidase and β-glucosidase) and decrease (peroxidase, N-acetyl-glucosaminidase and acid phosphatase) of enzyme activities were observed in biochar treatments, but only peroxidase activity showed statistical significance (at least p < 0.01) compared to the control. Moreover, the activities of all enzymes tested were significantly related to the content of biochar addition (at least p < 0.05). On the other hand, bacterial and fungal abundance in biochar treatments were remarkably lower than control (p < 0.001), and the significantly negative relationship (p < 0.05) between bacterial abundance and the content of biochar was found. Additionally, the increased percentage of organic C gradually increased with biochar addition rate, which provided evidence for applying biochar to mitigate climate change. Given the importance of microorganisms and enzyme activities in sediment organic matter decomposition, the increased C sequestration might be explained by the large decrease of microbial abundance and enzyme activity after biochar intervention.

Trace element concentration in surface sediments of Palk Strait, southeast coast of Tamil Nadu, India

The present work was carried to decipher the trace element accumulation in surface sediments of Palk Strait, southeast coast of Tamil Nadu, India. The elemental concentration and correlation results suggest that fine fractions with CaCO3 content followed by organic matter (OM) of the surface sediments control the trace element accumulation in the study area. In addition, Fe and Mn concentration is chiefly contributed from riverine process and controlled by the mangrove ecosystem. The other elements are derived into marine environment through confluence of untreated industrial pollutants into the river system. The EF result shows that the studied marine sediments are enriched by Ni, Mn, Cu, Pb, Cd, Cr, followed by Zn. The order of the pollution intensity with respect to geo-accumulation index suggests the following ascending order: Ni>Mn>Fe>Cu>Pb>Cd>Cr>Zn. Pollution Load Index (PLI) values reveal that all the samples are falling under moderately to unpolluted category.

Bioactive metabolites produced by Streptomyces Cheonanensis VUK-A from Coringa mangrove sediments: isolation, structure elucidation and bioactivity

The strain VUK-A was isolated from a sediment sample of the Coringa mangrove ecosystem was identified as Streptomyces cheonanensis based on morphological, physiological, biochemical and molecular properties. Chemical investigation of the secondary metabolites of the strain Streptomyces cheonanensis VUK-A has led to the segregation of two bioactive compounds, namely 2-Methyl butyl propyl phthalate (1) and Diethyl phthalate (2) using column chromatography. The chemical structure of the active compounds was established on the basis of spectroscopic analysis, including ¹H NMR and ¹³C NMR spectroscopies, FTIR and EIMS. The antimicrobial activity of the bioactive compounds produced by the strain was tested against a wide variety of bacteria and fungi and expressed in terms of minimum inhibitory concentration. The compounds (1&2) were active against all the bacteria tested, and the best activity of compound 1 was recorded against Proteus vulgaris (4 µg/ml). Compounds (1&2) were active against dermatophytes and fungi but compound 1 displayed high antifungal activity against Candida albicans (8 µg/ml) and Fusarium solani (16 µg/ml) compared to standard antifungal agents. The cytotoxicity of the bioactive compound 1 was tested against MDA-MB-231, OAW-42, HeLa, and MCF-7 cell lines. The highest activity of 100 µM by compound 1 was recorded against HeLa cancer cell lines. In fact, this is the first report of 2-Methyl butyl propyl phthalate from the genus Streptomyces.

Distribution, diversity and abundance of bacterial laccase-like genes in different particle size fractions of sediments in a subtropical mangrove ecosystem

This study investigated the diversity and abundance of bacterial lacasse-like genes in different particle size fractions, namely sand, silt, and clay of sediments in a subtropical mangrove ecosystem. Moreover, the effects of nutrient conditions on bacterial laccase-like communities as well as the correlation between nutrients and, both the abundance and diversity indices of laccase-like bacteria in particle size fractions were also studied. Compared to bulk sediments, Bacteroidetes, Caldithrix, Cyanobacteria and Chloroflexi were dominated in all 3 particle-size fractions of intertidal sediment (IZ), but Actinobacteria and Firmicutes were lost after the fractionation procedures used. The diversity index of IZ fractions decreased in the order of bulk > clay > silt > sand. In fractions of mangrove forest sediment (MG), Verrucomicrobia was found in silt, and both Actinobacteria and Bacteroidetes appeared in clay, but no new species were found in sand. The declining order of diversity index in MG fractions was clay > silt > sand > bulk. Furthermore, the abundance of lacasse-like bacteria varied with different particle-size fractions significantly (p < 0.05), and decreased in the order of sand > clay > silt in both IZ and MG fractions. Additionally, nutrient availability was found to significantly affect the diversity and community structure of laccase-like bacteria (p < 0.05), while the total organic carbon contents were positively related to the abundance of bacterial laccase-like genes in particle size fractions (p < 0.05). Therefore, this study further provides evidence that bacterial laccase plays a vital role in turnover of sediment organic matter and cycling of nutrients.