Benthic archaeal community structure and carbon metabolic profiling of heterotrophic microbial communities in brackish sediments.

Benthic Archaea play a crucial role in the biogeochemical cycles and food webs, however, their spatiotemporal distribution and environmental drivers are not well investigated in brackish sediments. The composition and abundances of benthic archaeal communities were examined from a coastal lagoon; Chilika (India) which is experiencing an intense pressure from anthropogenic and natural factors. High-throughput sequencing of 16S rRNA genes revealed that sediment (n = 96) archaeal communities were largely composed of Crenarchaeota (18.76%), Euryarchaeota (18.34%), Thaumarchaeota (13.45%), Woesearchaeota (10.05%), and Pacearchaeota (4.21%). Archaeal taxa affiliated to methanogens, sulfate-reducers, and ammonia-oxidizers were detected suggesting that carbon, sulfur, and nitrogen cycles might be prominent in benthic sediments. Salinity, total organic carbon, available nitrogen, available phosphorus, macrophyte (Phragmites karka) and inter-taxa relationships between community members and with bacterial communities played steering roles in structuring the archaeal communities. Marine sites with mesohaline-polyhaline regime were dominated by Nitrosopumilus and Thaumarchaeota. In contrast, riverine sites with oligohaline regime demonstrated a higher abundance of Thermoprotei. Macrophyte dominated zones were enriched in Methanomicrobia and Methanobacteria in their rhizosphere sediments, whereas, bulk (un-vegetated) sediments were dominated by Nitrosopumilus. Spatial patterns in archaeal communities demonstrated 'distance-decay' patterns which were correlated with changes in physicochemical factors over geographical distances. Heterotrophic microbial communities showed much higher metabolic diversity and activity in their carbon utilization profiles in rhizosphere sediments than the bulk sediments. This baseline information on benthic archaea and their environmental drivers would be useful to assess the impact of anthropogenic and natural pressures on these communities and associated biogeochemical cycles.

Seasonal and spatial dynamics of bacterioplankton communities in a brackish water coastal lagoon.

Coastal ecosystems, one of the most productive ecosystems, are subjected to natural and anthropogenic stresses. Coastal bacterioplankton communities are highly dynamic due to spatiotemporal heterogeneity in the environmental parameters. We investigated the seasonal and spatial variation in bacterioplankton communities, their abundances and environmental drivers during one year period in Chilika, a brackish water coastal lagoon of India. High-throughput sequencing of 16S rRNA genes of bacterioplankton communities showed that they were dominated by heterotrophs namely α-Proteobacteria SAR11 and their sub-clades (SAR11_Ib, Chesapeake-Delaware_Bay, Candidatus_Pelagibacter, and SAR11_Surface_1), actinobacterial lineages (hgcI, CL500-29, and Candidatus_Aquiluna), ß-Proteobacteria MWH-UniP1, ß-Proteobacteria OM43, and verrucomicrobial clade Spartobacteria 'LD29'. Synechococcus was the dominant member within autotrophic cyanobacterial community. Response ratio derived from comparisons of taxon-specific absolute abundances and indicator analyses showed that SAR11_Surface_1 sub-clade occupied high-salinity environment especially during summer and winter and emerged as a strong indicator for mesohaline-polyhaline salinity regime. In contrast, Spartobacteria 'LD29', Actinobacteria hgcI, and CL500-29 preferred low-salinity freshwater environment and were strong indicators for oligohaline-mesohaline regimes. Spatiotemporal patterns were governed by 'distance-decay' and 'similarity-time' relationships. Bacterioplankton communities were mostly determined by salinity, dissolved oxygen, phosphate, and pH which resulted 'species sorting' leading to biogeographical patterns in the bacterioplankton communities. Modeling analysis revealed the characteristic shift in the indicator bacterioplankton taxa along with estuarine salinity gradient. This study has provided baseline information on the bacterioplankton communities and their environmental drivers within an anthropogenically impacted cyclone prone coastal lagoon which would be useful in assessing the impact of multiple stressors on this vulnerable ecosystem.

Spatial and temporal heterogeneity in the structure and function of sediment bacterial communities of a tropical mangrove forest.

Bacterial communities of mangrove sediments are well appreciated for their role in nutrient cycling. However, spatiotemporal variability in these communities over large geographical scale remains understudied. We investigated sediment bacterial communities and their metabolic potential in an intertidal mangrove forest of India, Bhitarkanika, using high-throughput sequencing of 16S rRNA genes and community-level physiological profiling. Bulk surface sediments from five different locations representing riverine and bay sites were collected over three seasons. Seasonality largely explained the variation in the structural and metabolic patterns of the sediment bacterial communities. Freshwater Actinobacteria were more abundant in monsoon, whereas γ-Proteobacteria demonstrated higher abundance in summer. Distinct differences in the bacterial community composition were noted between riverine and bay sites. For example, salt-loving marine bacteria affiliated to Oceanospirillales were more prominent in the bay sites than the riverine sites. L-asparagine, N-acetyl-D-glucosamine, and D-mannitol were the preferentially utilized carbon sources by bacterial communities. Bacterial community composition was largely governed by salinity and organic carbon content of the sediments. Modeling analysis revealed that the abundance of δ-Proteobacteria increased with salinity, whereas ß-Proteobacteria displayed an opposite trend. Metabolic mapping of taxonomic data predicted biogeochemical functions such as xylan and chitin degradation, ammonia oxidation, nitrite reduction, and sulfate reduction in the bacterial communities suggesting their role in carbon, nitrogen, and sulfur cycling in mangrove sediments. This study has provided valuable clues about spatiotemporal heterogeneity in the structural and metabolic patterns of bacterial communities and their environmental determinants in a tropical mangrove forest.

Taxonomic description and draft genome of Pseudomonas sediminis sp. nov., isolated from the rhizospheric sediment of Phragmites karka.

The taxonomic position of a Gram-stain-negative, rod-shaped bacterial strain, designated PI11T, isolated from the rhizospheric sediment of Phragmites karka was characterized using a polyphasic approach. Strain PI11T could grow optimally at 1.0% NaCl concentration with pH 7.0 at 30°C and was positive for oxidase and catalase but negative for hydrolysis of starch, casein, and esculin ferric citrate. Phylogenetic analysis of 16S rRNA gene sequences indicated that the strain PI11T belonged to the genus Pseudomonas sharing the highest sequence similarities with Pseudomonas indoloxydans JCM 14246T (99.72%), followed by, Pseudomonas oleovorans subsp. oleovorans DSM 1045T (99.29%), Pseudomonas toyotomiensis JCM 15604T (99.15%), Pseudomonas chengduensis DSM 26382T (99.08%), Pseudomonas oleovorans subsp. lubricantis DSM 21016T (99.08%), and Pseudomonas alcaliphila JCM 10630T (99.01%). Experimental DNA-DNA relatedness between strain PI11T and P. indoloxydans JCM 14246T was 49.4%. The draft genome of strain PI11T consisted of 4,884,839 bp. Average nucleotide identity between the genome of strain PI11T and other closely related type strains ranged between 77.25-90.74%. The polar lipid pattern comprised of phosphatidylglycerol, diphosphatidylglycerol, and phosphatidylcholine. The major (> 10%) cellular fatty acids were C18:1ω6c/ω7c, C16:1ω6c/ω7c, and C16:0. The DNA G + C content of strain PI11T was 62.4 mol%. Based on the results of polyphasic analysis, strain PI11T was delineated from other closely related type strains. It is proposed that strain PI11T represents represents a novel species of the genus Pseudomonas, for which the name Pseudomonas sediminis sp. nov. is proposed. The type strain is PI11T (= KCTC 42576T = DSMZ 100245T).

Salinity and macrophyte drive the biogeography of the sedimentary bacterial communities in a brackish water tropical coastal lagoon.

Brackish water coastal lagoons are least understood with respect to the seasonal and temporal variability in their sedimentary bacterial communities. These coastal lagoons are characterized by the steep environmental gradient and provide an excellent model system to decipher the biotic and abiotic factors that determine the bacterial community structure over time and space. Using Illumina sequencing of the 16S rRNA genes from a total of 100 bulk surface sediments, we investigated the sedimentary bacterial communities, their spatiotemporal distribution, and compared them with the rhizosphere sediment communities of a common reed; Phragmites karka and a native seagrass species; Halodule uninervis in Chilika Lagoon. Spatiotemporal patterns in bacterial communities were linked to specific biotic factors (e.g., presence and type of macrophyte) and abiotic factors (e.g., salinity) that drove the community composition. Comparative assessment of communities highlighted bacterial lineages that were responsible for segregating the sediment communities over distinct salinity regimes, seasons, locations, and presence and type of macrophytes. Several bacterial taxa were specific to one of these ecological factors suggesting that species-sorting processes drive specific biogeographical patterns in the bacterial populations. Modeling of proteobacterial lineages against salinity gradient revealed that α- and γ-Proteobacteria increased with salinity, whereas ß-Proteobacteria displayed the opposite trend. The wide variety of biogeochemical functions performed by the rhizosphere microbiota of P. karka must be taken into consideration while formulating the management and conservation plan for this reed. Overall, this study provides a comprehensive understanding of the spatiotemporal dynamics and functionality of sedimentary bacterial communities and highlighted the role of biotic and abiotic factors in generating the biogeographical patterns in the bacterial communities of a tropical brackish water coastal lagoon.

Mangrovibacter phragmitis sp. nov., an endophyte isolated from the roots of Phragmites karka.

A facultatively anaerobic, Gram-stain-negative, rod-shaped, nitrogen-fixing, endophytic bacterial strain designated MP23T was isolated from the roots of Phragmites karka growing in Chilika Lagoon, Odisha, India. Strain MP23T was slightly halophilic, and the optimal NaCl concentration and temperature for growth were 1 % and 30 °C, respectively. On the basis of 16S rRNA gene sequence similarities, strain MP23T was affiliated to the family Enterobacteriaceae and most closely related to Mangrovibacter yixingensis KCTC 42181T and Mangrovibacter plantisponsor DSM 19579T with 99.71 % similarity, followed by Salmonella enterica subsp. salamae DSM 9220T (97.22 %), Cronobacter condimenti LMG 26250T (97.14 %) and Salmonella enterica subsp. diarizonae DSM 14847T (97 %). Sequence analysis of 16S rRNA, hsp60, gyrB and rpoB genes showed that strain MP23T formed a phylogenetic cluster with M. yixingensis KCTC 42181T and M. plantisponsor DSM 19579T indicating that it belongs to the genus Mangrovibacter. The major cellular fatty acids were C16 : 0, C18 : 1ω6c and/or C18 : 1ω7c, C16 : 1ω6c and/or C16 : 1ω7c, C14 : 0, C14 : 0 3-OH and/or iso-C16 : 1 I and C17 : 0 cyclo. Polar lipids of strain MP23T consisted of phosphatidylglycerol, diphosphatidylglycerol and phosphatidylethanolamine. The DNA G+C content was 50.3 mol%. Based on experimental DNA-DNA hybridization values and average nucleotide identity derived from in silico comparison of whole-genome sequences, strain MP23T could be distinguished from its closest neighbours. We therefore conclude that strain MP23T represents a novel species of the genus Mangrovibacter for which the name Mangrovibacter phragmitis sp. nov. is proposed. The type strain is MP23T (=DSM 100250T=KCTC 42580T).

The draft genome sequence of Mangrovibacter sp. strain MP23, an endophyte isolated from the roots of Phragmites karka.

Till date, only one draft genome has been reported within the genus Mangrovibacter. Here, we report the second draft genome shotgun sequence of a Mangrovibacter sp. strain MP23 that was isolated from the roots of Phargmites karka (P. karka), an invasive weed growing in the Chilika Lagoon, Odisha, India. Strain MP23 is a facultative anaerobic, nitrogen-fixing endophytic bacteria that grows optimally at 37 °C, 7.0 pH, and 1% NaCl concentration. The draft genome sequence of strain MP23 contains 4,947,475 bp with an estimated G + C content of 49.9% and total 4392 protein coding genes. The genome sequence has provided information on putative genes that code for proteins involved in oxidative stress, uptake of nutrients, and nitrogen fixation that might offer niche specific ecological fitness and explain the invasive success of P. karka in Chilika Lagoon. The draft genome sequence and annotation have been deposited at DDBJ/EMBL/GenBank under the accession number LYRP00000000.