Metagenomic 16s rRNA investigation of microbial communities in the Black Sea estuaries in South-West of Ukraine

Effects of environmental parameters on spatial and temporal distribution of marine microbial communities in the southern Black Sea

The Black Sea is a unique environment with strong and permanent vertical stratification, with a thin layer of oxic zone above and a permanent anoxic zone below. Few high-throughput genomic surveys have been conducted to examine microbiota in the Black Sea. Yet, there is no study on the seasonal and vertical variation in microbial community compositions, driving forces and mechanisms of community assembly. In this study, seasonal, vertical, and spatial microbial assemblages were studied in terms of diversity, abundance, and community structure using 16S rRNA metabarcoding. 16S rRNA metabarcoding confirmed seasonal changes in microbial communities and the presence of distinct microbial groups among different water layers. Taxa belonging to Cyanobiaceae contributed a large fraction of the total biomass and were the most abundant autotrophic bacteria found across the whole water column, including hydrogen sulfide-containing anoxic zone. Temperature, salinity, water density, conductivity, light, chlorophyll-a, O2, NO3, NH3, PO4, Si, and H2S had a significant influence on the vertical bacterial community assemblages. The copper mine discharge system at 180 m did not affect microbial community structure and composition. Temperature seemed to be a primary factor in the variance between shallow depths. In conclusion, the lack of light, low dissolved oxygen levels, and low temperature do not restrict microbial diversity, as proven by the higher diversity observed in deeper zones. Wastewater in Black Sea region may be discharged into the Black Sea to depth of 180 m or deeper without impacting microbial ecology.

Deep-sea sediment metagenome from Bay of Bengal reveals distinct microbial diversity and functional significance

Bay of Bengal (BoB) has immense significance with respect to ecological diversity and natural resources. Studies on microbial profiling and their functional significance at sediment level of BoB remain poorly represented. Herein, we describe the microbial diversity and metabolic potentials of BOB deep-sea sediment samples by subjecting the metagenomes to Nanopore sequencing. Taxonomic diversity ascertained at various levels revealed that bacteria belonging to phylum Proteobacteria predominantly represented in sediment samples NIOT_S7 and NIOT_S9. A comparative study with 16S datasets from similar ecological sites revealed depth as a crucial factor in determining taxonomic diversity. KEGG annotation indicated that bacterial communities possess sequence reads corresponding to carbon dioxide fixation, sulfur, nitrogen metabolism, but at varying levels. Additionally, gene sequences related to bioremediation of dyes, plastics, hydrocarbon, antibiotic resistance, secondary metabolite synthesis and metal resistance from both the samples as studied indicate BoB to represent a highly diverse environmental niche for further exploration.

Influence of hydrological factors on bacterial community structure in a tropical monsoonal estuary in India

In the present study, we analyzed variations in bacterial community structure along a salinity gradient in a tropical monsoonal estuary (Cochin estuary [CE]), on the southwest coast of India, using Illumina next-generation sequencing (NGS). Water samples were collected from eight different locations thrice a year to assess the variability in the bacterial community structure and to determine the physico-chemical factors influencing the bacterial diversity. Proteobacteria was the most dominant phyla in the estuary followed by Bacteroidetes, Cyanobacteria, Actinobacteria, and Firmicutes. Statistical analysis indicated significant variations in bacterial communities between freshwater and mesohaline and euryhaline regions, as well as between the monsoon (wet) and nonmonsoon (dry) periods. The abundance of Betaproteobacteria was higher in the freshwater regions, while Alphaproteobacteria and Epsilonproteobactera were more abundant in mesohaline and euryhaline regions of the estuary. Gammaproteobacteria was more abundant in regions with high nutrient concentrations. Various bacterial genera indicating the presence of fecal contamination and eutrophication were detected. Corrplot based on Pearson correlation analysis demonstrated the important physico-chemical variables (temperature, salinity, dissolved oxygen, and inorganic nutrients) that influence the distribution of dominant phyla, class, and genera. The observed spatio-temporal variations in bacterial community structure in the CE were governed by regional variations in anthropogenic inputs and seasonal variations in monsoonal rainfall and tidal influx.

Microbial Diversity and Phage-Host Interactions in the Georgian Coastal Area of the Black Sea Revealed by Whole Genome Metagenomic Sequencing

Viruses have the greatest abundance and highest genetic diversity in marine ecosystems. The interactions between viruses and their hosts is one of the hot spots of marine ecology. Besides their important role in various ecosystems, viruses, especially bacteriophages and their gene pool, are of enormous interest for the development of new gene products with high innovation value. Various studies have been conducted in diverse ecosystems to understand microbial diversity and phage-host interactions; however, the Black Sea, especially the Eastern coastal area, remains among the least studied ecosystems in this regard. This study was aimed at to fill this gap by analyzing microbial diversity and bacteriophage-host interactions in the waters of Eastern Black Sea using a metagenomic approach. To this end, prokaryotic and viral metagenomic DNA from two sampling sites, Poti and Gonio, were sequenced on the Illumina Miseq platform and taxonomic and functional profiles of the metagenomes were obtained using various bioinformatics tools. Our metagenomics analyses allowed us to identify the microbial communities, with Proteobacteria, Cyanobacteria, Actinibacteria, and Firmicutes found to be the most dominant bacterial phyla and Synechococcus and Candidatus Pelagibacter phages found to be the most dominant viral groups in the Black Sea. As minor groups, putative phages specific to human pathogens were identified in the metagenomes. We also characterized interactions between the phages and prokaryotic communities by determining clustered regularly interspaced short palindromic repeats (CRISPR), prophage-like sequences, and integrase/excisionase sequences in the metagenomes, along with identification of putative horizontally transferred genes in the viral contigs. In addition, in the viral contig sequences related to peptidoglycan lytic activity were identified as well. This is the first study on phage and prokaryote diversity and their interactions in the Eastern coastal area of the Black Sea using a metagenomic approach.

Holistic pelagic biodiversity monitoring of the Black Sea via eDNA metabarcoding approach: From bacteria to marine mammals

As the largest semi-closed marine ecosystem in the world, the Black Sea has been heavily affected by human activities for a long time. Describing the biodiversity of multi-trophic biota in pelagic zone of the Black Sea and identifying the dominant environmental factors are prerequisites for protecting the sustainability of ecosystems. However, up to now, the taxonomic and distributional information about the Black Sea biota is not clear. Here, we employed a Tree-of-Life metabarcoding to analyze the biodiversity of eight communities in the Black Sea, investigated their biogeographical distribution, and further analyzed the influence of biological and abiotic factors on biota on large scales. We found that, (1) Over 8900 OTUs were detected in the Black Sea, of which 630 species were identified, covering the holistic biota from single-celled (bacteria 5620 OTUs 141 species; algae 1096 OTUs 185 species; protozoa 546 OTUs 146 species) to multicellular organisms (invertebrate metazoans 150 OTUs 34 species; fishes 1369 OTUs 76 species; large marine mammals 39 OTUs 5 species). (2) Higher trophic organisms (fishes and large mammals) distributed more evenly in space than the lower (microorganisms, protozoa and invertebrates). For lower trophic organisms, the vertical stratification was more obvious than the horizontal stratification (vertical p < 0.02, horizontal p < 0.05). (3) The bottom trophic organisms (bacteria and algae) of the food web significantly affected the distribution and composition of the others through biological interactions (Mantel p < 0.05). (4) At the level of abiotic factors, the effect of local species sorting on the composition of communities was 15% higher than that of mass dispersal effect. For the first time, this study monitored and profiled the holistic biodiversity in the pelagic zone of the Black Sea, and provided technological advances and preliminary knowledge for the ongoing Black Sea ecosystem protection efforts.

Characteristics of microbial communities and intestinal pathogenic bacteria for migrated Larus ridibundus in southwest China

Larus ridibundus, a migratory wild bird, has become one of the most popular gull species in southwest China in recent years. There has been no information on the gut microbiota and intestinal pathogenic bacteria configuration in wild L. ridibundus, even though the public are in close contact with this bird. In this study, 16S rRNA amplicon‐sequencing methods were used to describe the microbial community structure and intestinal pathogenic bacteria were isolated to identify their characteristics. The taxonomic results revealed that Firmicutes (86%), Proteobacteria (10%), and Tenericutes (3%) were the three most abundant phyla in the gut of L. ridibundus. Enterococcaceae, Enterobacteriaceae, and Mycoplasmataceae were the most predominant families, respectively. The number of operational taxonomic units (OTUs), the richness estimates and diversity indices of microbiota, was statistically different (p < 0.05). However, beta diversity showed that no statistical significance (p > 0.05) between all the fecal samples. The most frequently isolated intestinal pathogenic bacteria from L. ridibundus were enteropathogenic Escherichia coli (32%) and Salmonella (21%). Pulsed‐field gel electrophoresis (PFGE) results of Salmonella species revealed a high degree of similarity between isolates, which was not observed for other species. None of the potentially pathogenic isolates were identical to human‐isolated counterparts suggesting that there was little cross‐infection between humans and gulls, despite close proximity. In brief, this study provided a baseline for future L. ridibundus microbiology analysis, and made an understanding of the intestinal bacterial community structure and diversity.

Sediment microbial taxonomic and functional diversity in a natural salinity gradient challenge Remane's "species minimum" concept

Several models have been developed for the description of diversity in estuaries and other brackish habitats, with the most recognized being Remane’s Artenminimum (“species minimum”) concept. It was developed for the Baltic Sea, one of the world’s largest semi-enclosed brackish water body with a unique permanent salinity gradient, and it argues that taxonomic diversity of macrobenthic organisms is lowest within the horohalinicum (5 to 8 psu). The aim of the present study was to investigate the relationship between salinity and sediment microbial diversity at a freshwater-marine transect in Amvrakikos Gulf (Ionian Sea, Western Greece) and assess whether species composition and community function follow a generalized concept such as Remane’s. DNA was extracted from sediment samples from six stations along the aforementioned transect and sequenced for the 16S rRNA gene using high-throughput sequencing. The metabolic functions of the OTUs were predicted and the most abundant metabolic pathways were extracted. Key abiotic variables, i.e., salinity, temperature, chlorophyll-a and oxygen concentration etc., were measured and their relation with diversity and functional patterns was explored. Microbial communities were found to differ in the three habitats examined (river, lagoon and sea) with certain taxonomic groups being more abundant in the freshwater and less in the marine environment, and vice versa. Salinity was the environmental factor with the highest correlation to the microbial community pattern, while oxygen concentration was highly correlated to the metabolic functional pattern. The total number of OTUs showed a negative relationship with increasing salinity, thus the sediment microbial OTUs in this study area do not follow Remane’s concept.

Metagenomic profiling of the microbial freshwater communities in two Bulgarian reservoirs

Microorganisms inhabiting freshwater environments are an integral part of the aquatic ecosystems. Very few data are available regarding the profiles of the microbial communities in the reservoirs in Bulgaria, despite their key role in the biogeochemical processes. In the present study, we provide the first comprehensive metagenomic analysis on the planktonic bacterial diversity of two large and economically important Bulgarian reservoirs (Batak and Tsankov Kamak) using next-generation sequencing of 16S ribosomal RNA gene (16S rRNA). Analysis of the metagenomic amplicon datasets, including quality filtering, clustering of Operational Taxonomic Units and taxonomy assignment revealed that 78.45% of the microbial communities between the two reservoirs were overlapping. The diversity (H) and Pielou's evenness (J) indices declined along the longitudinal axis of both reservoirs. The estimated values for the Shannon diversity index are typically observed in oligotrophic lakes. The microbial communities of both reservoirs were dominated by Proteobacteria, followed by Actinobacteria and Bacteroidetes all comprised over 95% of the relative abundance, regardless of the reservoir's large hydrogeological differences. The bacterioplankton was characterized by high phylogenetic heterogeneity in the taxonomic structure, being distributed among 211 genera. The genera Limnohabitans and Rhodoferax held the absolute predominance, implying their significance in the aquatic food webs. The obtained data can contribute to the better systematic understanding of the microbial diversity of freshwater environments.