Changing Tropical Estuarine Sedimentary Environments with Time and Metals Contamination, Cest Coast of India

Estuaries are one of the major sub-environments of the coastal zone wherein freshwaters interact and mix with saline waters, and facilitate deposition of finer sediments, organic matter, and metals. Intertidal mudflat and mangrove sediment cores collected from estuaries along the central west coast of India were investigated for various sedimentological and geochemical parameters to understand the changes in the sedimentary depositional environments and various factors influencing the processes. Additionally, estuarine biota was examined to understand the bioaccumulation of metals with respect to bioavailability. The results indicated considerable changes in the depositional environments with time owing to sea-level changes; geomorphology of the estuaries; rainfall and river runoff; anthropogenic activities including construction of dams and bridges. The sediments in the estuaries are considerably polluted by metals and pose toxicity risks to the estuarine biota due to high metal bioavailability. Marine gastropods and mangrove plants act as prospective bio-indicators, and the bioremediation potential of mangroves for contaminated sediments was identified. Metal bioaccumulation in edible benthic biota can be harmful to the human health.

Acuticoccus mangrovi sp. nov., with an antibacterial property, isolated from mangrove sediment

A Gram-stain-negative, aerobic, milky white bacterium, designated B2012T, was isolated from mangrove sediment collected at Beibu Gulf, South China Sea. Antimicrobial activity assay revealed that the isolate possesses the capability of producing antibacterial compounds. Strain B2012T shared the highest 16S rRNA gene sequence relatedness (96.9–95.5 %) with members of the genus Acuticoccus . The isolate and all known Acuticoccus species contain Q-10 as the main respiratory quinone and have the same polar lipid components (phosphatidylcholine, unidentified glycolipid, unidentified lipid, unidentified amino lipid and phosphatidylglycerol). However, genomic relatedness referred by values of average nucleotide identity, digital DNA–DNA hybridization, average amino acid identity and the percentage of conserved proteins between strain B2012T and other type strains of the genus Acuticoccus were below the proposed thresholds for species discrimination. The genome of strain B2012T was assembled into 65 scaffolds with an N50 size of 244239 bp, resulting in a 5.5 Mb genome size. Eight secondary metabolite biosynthetic gene clusters were detected in this genome, including three non-ribosomal peptide biosynthetic loci encoding yet unknown natural products. Strain B2012T displayed moderately halophilic and alkaliphilic properties, growing optimally at 2–3 % (w/v) NaCl concentration and at pH 8–9. The major cellular fatty acids (>10 %) were anteiso-C15 : 0, C16 : 0 dimethyl aldehyde (DMA) and C16 : 0. Combined data from phenotypic, genotypic and chemotaxonomic analyses suggested that strain B2012T represents a novel species of the genus Acuticoccus , for which the name Acuticoccus mangrovi sp. nov. is proposed. The type strain of the type species is B2012T (=MCCC 1K04418T=KCTC 72962T).

Marinobacter mangrovi sp. nov., isolated from mangrove sediment

A novel marine bacterium, designated strain CHFG3-1-5T, was isolated from mangrove sediment sampled at Jiulong River estuary, Fujian, PR China. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain CHFG3-1-5T belonged to the genus Marinobacter , with the highest sequence similarity to Marinobacter segnicrescens SS011B1-4T (97.6%), followed by Marinobacter nanhaiticus D15-8WT (97.5%), Marinobacter bohaiensis T17T (97.1%) and Marinobacter hydrocarbonoclasticus SP.17T (90.6%). The bacterium was Gram-stain-negative, facultative anaerobic, oxidase- and catalase-positive, rod-shaped and motile with a polar flagellum. Strain CHFG3-1-5T grew optimally at 32–37 °C, pH 6.0–8.0 and in the presence of 2.0–3.0% (w/v) NaCl. The G+C content of the chromosomal DNA was 61.1 mol%. The major respiratory quinone was determined to be Q-9. The principal fatty acids were C16 : 0, summed feature 3 (C16 : 1 ω7c/ω6c), C12 : 0, summed feature 9 (C17 : 1 iso ω9c and/or C16 : 0 10-methyl), C12 : 0 3-OH and summed feature 8 (C18 : 1 ω7c and/or C18 : 1 ω6c). The polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, three phospholipids, one glycolipid and two aminolipids. The average nucleotide identity and digital DNA–DNA hybridization values among the genomes of strain CHFG3-1-5T and the reference strains were 73.4–79.4 and 19.6–22.4%, respectively. Like many other species reported in the genus Marinobacter , strain CHFG3-1-5T was able to oxidise iron. The combined genotypic and phenotypic data showed that strain CHFG3-1-5T represents a novel species within the genus Marinobacter , for which the name Marinobacter mangrovi sp. nov. is proposed, with the type strain CHFG3-1-5T (=MCCC 1A18306T=KCTC 82398T).

Fusibacter ferrireducens sp. nov., an anaerobic, Fe(Ⅲ)- and sulphur-reducing bacterium isolated from mangrove sediment

An anaerobic, alkaliphilic, halotolerant, Gram-stain-positive and rod-shaped bacterium, designated Q10-2T, was isolated from mangrove sediment sampled at the Jiulong river estuary, PR China. The cells of strain Q10-2T were motile and 0.5×2–4 µm in size. Strain Q10-2T grew at 8–45 °C (optimum, 32 °C), at pH 7.0–10.5 (optimum, pH 8.5) and in the presence of 0–6 % (w/v) NaCl (optimum, 3 %). It could use complex organic compounds and carbohydrates including d-fructose, d-galactose, d-glucose, d-mannitol, d-xylose, trehalose, lactose, maltose, sucrose and starch as carbon sources and electron donors. It could reduce sulphate, thiosulphate and elemental sulphur to sulphide, but not sulphite. Fe (Ⅲ) citrate, ferrihydrite, haematite and goethite in the presence of glucose as the electron donor were also reduced. Acetate, butyrate, ethanol, CO2 and H2 were end products of glucose fermentation. The predominant cellular fatty acids were composed of C14 : 0, C16 : 0 and summed features containing C16 : 1 ω7c and/or iso-C15 : 0 2-OH and iso-C17 : 1 and/or anteiso-C17 : 1 B. Phylogenetic analysis based on 16S rRNA gene sequences indicated that the novel strain was most closely related to Fusibacter paucivorans DSM 12116T (95.5 % sequence similarity). The genome size of strain Q10-2T was 5.0 Mb, with a G+C content of 37.4 mol%. The average nucleotide identity and digital DNA–DNA hybridization values between strain Q10-2T and F. paucivorans DSM 12116T were 69.1 and 21.8 %, respectively. The combined genotypic and phenotypic data showed that strain Q10-2T represents a novel species of the genus Fusibacter , for which the name Fusibacter ferrireducens sp. nov. is proposed. The type strain is Q10-2T (=MCCC 1A16257T=KCTC 15906T).