Nutrient supply controls the linkage between species abundance and ecological interactions in marine bacterial communities

Nutrient scarcity is pervasive for natural microbial communities, affecting species reproduction and co-existence. However, it remains unclear whether there are general rules of how microbial species abundances are shaped by biotic and abiotic factors. Here we show that the ribosomal RNA gene operon (rrn) copy number, a genomic trait related to bacterial growth rate and nutrient demand, decreases from the abundant to the rare biosphere in the nutrient-rich coastal sediment but exhibits the opposite pattern in the nutrient-scarce pelagic zone of the global ocean. Both patterns are underlain by positive correlations between community-level rrn copy number and nutrients. Furthermore, inter-species co-exclusion inferred by negative network associations is observed more in coastal sediment than in ocean water samples. Nutrient manipulation experiments yield effects of nutrient availability on rrn copy numbers and network associations that are consistent with our field observations. Based on these results, we propose a “hunger games” hypothesis to define microbial species abundance rules using the rrn copy number, ecological interaction, and nutrient availability.

Rheinheimera lutimaris sp. nov., a marine bacterium isolated from coastal sediment

A Gram-stain-negative, aerobic, rod-shaped bacterium, designated strain YQF-2T, was isolated from coastal sediment sampled in Jiangsu Province and characterized phylogenetically and phenotypically. Optimal bacterial growth occurred at 28 °C (range 4–38 °C) and pH 7 (pH 6–10). Phylogenetic analysis based on 16S rRNA gene sequences showed that strain YQF-2T was related to members of the genus Rheinheimera and shared the highest sequence identities with Rheinheimera pacifica KMM 1406T (98.6%), followed by Rheinheimera aestuarii H29T (98.4%), Rheinheimera japonica KMM 9513T (98.3%), Rheinheimera aquimaris SW-353T (98.3%), Rheinheimera hassiensis E48T (97.8%) and Rheinheimera muenzenbergensis E49T (97.7%). The 16S rRNA gene sequence identities between strain YQF-2T and other members of the genus Rheinheimera were below 97.2%. The digital DNA–DNA hybridization value between strain YQF-2T and R. pacifica KMM 1406T was 23.3±2.3%. The average nucleotide identity value between strain YQF-2T and R. pacifica KMM 1406T was 79.7%. The unique respiratory quinone was ubiquinone-8. Phosphatidylethanolamine and phosphatidylglycerol were identified as the major polar lipids. The strain had summed feature 3 (C16:1 ω7c and/or C16:1 ω6c), summed feature 8 (C18:1 ω7c and/or C18:1 ω6c), C16:0, C12:0 3-OH and iso-C17:0 3-OH as major fatty acids. The G+C content of the genomic DNA was 50.0 mol%. On the basis of phenotypic, genotypic and phylogenetic evidence, strain YQF-2T represents a novel species of the genus Rheinheimera , for which the name Rheinheimera lutimaris sp. nov. is proposed, with the type strain YQF-2T (=KCTC 72184T=MCCC 1K03663T).

The Rapidly Evolving Fudu Estuary Sandbar Lagoon Landform on the East Coast of the Bohai Sea: Recent Changes and Mechanism

The Fudu Estuary Sandbar Lagoon is one of the most representative sandbar-lagoon landforms in China, and has undergone drastic evolution in recent years, accompanied by increased coastal engineering activities. The evolution process and its control factors are studied through remote sensing interpretation and coastal sediment transport calculations. During 2010–2021, the sandbar quickly extended at an average speed of 49.5 m/a, but the annual growth has shown a decreasing trend in both area and width, and the shoreline has retreated by 25–45 m. The recent changes are the result of the combined action of natural conditions and human activities. Coastal sediment transport from west to east under the action of W-oriented waves is the natural cause of extension. An estuary dam and artificial island block the sediment transport path, and the material for the new growth of the sandbar comes from the erosion of its west side, which has directly caused the retreat and narrowing of the sandbar. The reduction in sediments from the river further aggravates the shrinkage. It is predicted that the sandbar will continue its eastward extension to connect with the coast in about 2–3 years. The erosion status is unlikely to change before the sediment supply is restored. Measures such as dismantling the estuary dam are recommended.

Bulk Chemical and Optical Spectroscopy Characterisations of Dissolved Organic Matter Extracted from the Tropical Coastal Sediment

The study of organic matter characterisation in coastal sediment is useful for understanding how dissolved organic matter (DOM) reactivity influences the fate of pollutants in the aquatic environment. However, there is little information available on the structural properties of DOM in coastal sediment. Chemical analysis, UV-Visible (UV-Vis) absorbance, fluorescence, and Fourier-transform infrared (FTIR) spectroscopy were used in this work to characterise and compare the components of water-extractable organic matter (WEOM) fractions from sediment from an estuary, a coastal area, and a port in Peninsular Malaysia, Malaysia. The elemental analysis (H/C and C/N ratios) of the three samples differed, which coincided with the findings of optical indices estimated from UV-Visible and fluorescent spectroscopy analyses. WEOM had an average output of 7.05 to 8.47 mg/L and was very dominating with heavy fraction organic carbon (HFOC). In DOM-KS and DOM-K sediments, the allochthonous component with a high degree of condensation and the aromatic compound was the dominating composition. Meanwhile, the DOM-KT possessed a high autochthonous composition as well as carboxylic and phenolic content. Correlation analysis indicates that the aromaticity index SUVA254 and humification index (HIX) have positive correlations. The combined results of the chemical and spectroscopic analyses indicate that different coastal ecosystems, with the integration of various human and land activities, produce variations in DOM in the coastal area.