DNA- and RNA-based bacterial communities and geochemical zonation under changing sediment porewater dynamics on the Aldabra Atoll

The remote Aldabra Atoll, Seychelles, provides the rare opportunity to study bacterial communities in pristine carbonate sediments across an entire biome. The four sampled sites cover sand with high porewater exchange, bioturbated silt and mud with intermediate exchange, as well as a seasonally and episodically desiccated landlocked pool. As sediments harbour dead cells and environmental DNA alongside live cells, we used bacterial 16S rRNA gene and transcript analysis to distinguish between past and present inhabitants. Previously described laminated sediments mirroring past conditions in the Cerin, France could not be retrieved. Thus, the aim was adjusted to determine whether bacterial community composition and diversity follow typical geochemical zonation patterns at different locations of the atoll. Our data confirm previous observations that diversity decreases with depth. In the lagoon, the bacterial community composition changed from Pseudomonas dominating in the sand to diverse mixed surface and sulphate reduction zones in the anaerobic mud with strongly negative Eh. The latter correlated with high total alkalinity, ammonia, and total sulphide, alongside a decrease in SO₄²⁻/Cl⁻ and high relative abundances of sulphate reducing (Halo-) Desulfovibrio, sulphur oxidizing Arcobacteraceae, photo(hetero)troph Cyanobacteria, Alphaproteobacteria, and fermenting Propionigenium. In contrast to expectations, deeper mud and pool sediments harboured high abundances of Halomonas or Alphaproteobacteria alongside high C/N and increased salinity. We believe that this atypical community shift may be driven by a change in the complexity of available organic matter.

Identification and characterization of an ectoine biosynthesis gene cluster from Aestuariispira ectoiniformans sp. nov., isolated from seawater

An ectoine-producing bacterium, designated SWCN16^T, was isolated from seawater and could be grown in a medium containing up to 12 % NaCl. A phylogenetic analysis based on 16S rRNA gene sequences revealed that strain SWCN16^T belonged to the genus Aestuariispira, class Alphaproteobacteria, and shared the highest 16S rRNA gene sequence similarity of 96.8% with Aestuariispira insulae CECT 8488^T. The phenotypic, chemotaxonomic, and genotypic characteristics findings of this study suggested that strain SWCN16^T represented a novel species of the genus Aestuariispira. We propose the name Aestuariispira ectoiniformans sp. nov. for this species. Whole-genome sequencing analysis of the isolate revealed a putative ectABC gene cluster for ectoine biosynthesis. These genes were found to be functional using ectoine synthesis testing and S16-ectBAC cells, which were pET21a-ectBAC-transformed E. coli BL21 cells. We found that S16-ectBAC synthesized about 1.67 g/L extracellular ectoine and about 0.59 g/L intracellular ectoine via bioconversion at optimum conditions.

Pacificispira spongiicola gen. nov., sp. nov., a nitrate-reducing bacterium isolated from tropical western Pacific

The Gram-stain-negative, strictly aerobic, curved-to-spiral rod-shaped bacterial strain, designated KN72^T, was isolated from the Caroline Seamounts in the Pacific Ocean. Phylogenetic analysis of 16S rRNA gene sequences revealed that strain KN72^T was a member of the family Rhodospirillaceae and formed a distinct lineage. Strain KN72^T contained ubiquinone-10 as the major respiratory quinone. The polar lipid profiles contained phosphatidylethanolamine, phosphatidylglycerol, one aminolipid and three phospholipids. The predominant cellular fatty acids were C_16:0 and summed feature 8 (comprising C_18:1ω7c/C_18:1ω6c). The strain KN72^T displayed highest 16S rRNA gene sequence similarities with Hwanghaeella grinnelliae Gri0909^T (92.3%), Marivibrio halodurans ZB80^T (91.0%) and Aestuariispira insulae AH-MY2^T (90.1%). The DNA G+C content of strain KN72^T was 61.1%. Collectively, based on phenotypic, chemotaxonomic, phylogenetic and genomic evidence presented, strain KN72^T represents a novel species of a novel genus of the family Rhodospirillaceae, for which the name Pacificispira spongiicola gen. nov., sp. nov. is proposed. The type strain is KN72^T (= CGMCC 1.17142^T = KCTC 72429^T).

Curvivirga aplysinae gen. nov., sp. nov., a marine bacterium isolated from the sea sponge Aplysina fistularis

A Gram-stain-negative, strictly aerobic, motile bacterium, designated strain RKSG073^T, was isolated from the sea sponge Aplysina fistularis, collected off the west coast of San Salvador, The Bahamas. Cells were curved-to-spiral rods with single, bipolar (amphitrichous) flagella, oxidase- and catalase-positive, non-nitrate-reducing and required salt for growth. RKSG073^T grew optimally at 30-37 °C, pH 6-7, and with 2-3 % (w/v) NaCl. The predominant fatty acids of RKSG073^T were summed feature 8 (C_18 : 1ω6c and/or C_18 : 1ω7c) and C_16 : 0. Major isoprenoid quinones were identified as Q-10 and Q-9. Phylogenetic analyses of nearly complete 16S rRNA genes and genome sequences positioned strain RKSG073^T in a clade with its closest relative Aestuariispira insulae AH-MY2^T (92.1 % 16S rRNA gene sequence similarity), which subsequently clustered with Hwanghaeella grinnelliae Gri0909^T, Marivibrio halodurans ZC80^T and type species of the genera Kiloniella, Thalassospira and Terasakiella. The DNA G+C content calculated from the genome of RKSG073^T was 42.2 mol%. On the basis of phylogenetic distinctiveness and polyphasic analysis, here we propose that RKSG073^T (culture deposit numbers: ATCC collection = TSD-74^T, BCCM collection = LMG 29869^T) represents the type strain of a novel genus and species within the family Kiloniellaceae, order Rhodospirillales and class Alphaproteobacteria, for which the name Curvivirga aplysinae gen. nov., sp. nov. is proposed.

Combined hormonal contraceptives are associated with minor changes in composition and diversity in gut microbiota of healthy women

Recent human and animal studies have found associations between gut microbiota composition and serum levels of sex hormones, indicating that they could be an important factor in shaping the microbiota. However, little is known about the effect of regular hormonal fluctuations over the menstrual cycle or CHC-related changes of hormone levels on gut microbiota structure, diversity and dynamics. The aim of this study was to investigate the effect of CHCs on human gut microbiota composition. The effect of CHC pill intake on gut microbiota composition was studied in a group of seven healthy pre-menopausal women using the CHC pill, compared to the control group of nine age-matched healthy women that have not used hormonal contraceptives in the 6 months prior to the start of the study. By analysing the gut microbiota composition in both groups during one menstrual cycle, we found that CHC usage is associated with a minor decrease in gut microbiota diversity and differences in the abundance of several bacterial taxa. These results call for further investigation of the mechanisms underlying hormonal and hormonal contraceptive-related changes of the gut microbiota and the potential implications of these changes for women's health.

Oleiliquidispirillum nitrogeniifigens gen. nov., sp. nov., a new member of the family Rhodospirillaceae isolated from oil reservoir water

A novel Gram-staining-negative, spiral-shaped bacterium, designated strain 64-1^T, was isolated from oil reservoir water collected from Liaohe oilfield, north-eastern China. Growth occurred at 15-55 °C and pH 6.0-10.0. The sole respiratory quinone was Q-10. The predominant cellular fatty acids were summed feature 8 (C_18 : 1  ω7c /C_18 : 1  ω6c), C_16 : 0 and C_19 : 0 cyclo ω8c. The polar lipids consisted of phosphatidylethanolamine (PE), phosphatidylglycerol (PG), phosphatidylcholine (PC), an unidentified aminophospholipid (UAPL), an unidentified aminolipid (UAL) and two unidentified polar lipids (UPL). The genomic DNA G+C content of strain 64-1^T was 64.5 mol%. Strain 64-1^T shared the highest 16S rRNA gene sequence similarities with Phaeospirillum chandramohanii JA145^T (92.0 %) and Telmatospirillum siberiense 26-4b1^T (91.8 %). In the phylogenetic trees, the strain constituted a sub-cluster within the family Rhodospirillaceae. Based on the results of morphological, physiological, biochemical and phylogenetic analysis, strain 64-1^T represents a new species of a novel genus within the family Rhodospirillaceae, for which the name Oleiliquidispirillum nitrogeniifigens gen. nov., sp. nov. is proposed. The type strain is 64-1^T (=CGMCC 1.16798^T=LMG 31399^T).

Current phylogeny of Rhodospirillaceae: A multi-approach study

Rhodospirillaceae represents a major family of the class alphaproteobacteria that includes an increasing number of functionally diverse taxa. The aim of this work is to evaluate the present phylogenetic diversity of the Rhodospirillaceae, which includes several metagenome-assembled genomes of uncultivated bacteria, as well as cultivated bacteria that were previously classified in different families. Various methodological approaches have been followed to discern the phylogenetic diversity of the taxa associated with the Rhodospirillaceae, which are grouped in three major sub-divisions and several other taxonomic entities that are currently confined to the genus rank. These genera include Tistrella, Elstera, Dongia and Ferrovibrio among cultivated organisms and alphaproteobacteria bacterium 41-28 among uncultivated bacteria. Overall, this study adds at least 11 genera and over 40 species to the current set of taxa belonging to the Rhodospirillaceae, a taxonomic term that clearly requires amendment. We propose to re-classify all taxa associated with the Rhodospirillaceae family under the new order, Diaforabacterales ord. nov. (from the Greek word for diversity, διάφορα). This study also uncovers the likely root of Rhodospirillaceae among recently reported metagenome-assembled genomes of uncultivated marine and groundwater bacteria.

Aestuariivivens insulae gen. nov., sp. nov., isolated from a tidal flat

A Gram-stain-negative, non-motile, aerobic, ovoid or rod-shaped bacterium, designated AH-MY3T, was isolated from a tidal flat on Aphae island of the south-western sea, South Korea, and subjected to a polyphasic taxonomic study. Strain AH-MY3T grew optimally at 35 °C, at pH 7.0–8.0 and in the presence of 2.0–3.0  % (w/v) NaCl. A neighbour-joining phylogenetic tree based on 16S rRNA gene sequences showed that strain AH-MY3T joined the cluster comprising the type strains of Yeosuana aromativorans, Snuella lapsa and Meridianimaribacter flavus, showing sequence similarities of 93.9, 93.7 and 92.6  %, respectively. Strain AH-MY3T exhibited 16S rRNA gene sequence similarity values of 94.0–94.7  % to the type strains of ‘Aestuariibaculum scopimerae’, Winogradskyella aquimaris, Winogradskyella poriferorum and Gaetbulibacter aestuarii. Strain AH-MY3T contained MK-6 as the predominant menaquinone. The fatty acid and polar lipid profiles of strain AH-MY3T could be distinguished from those of the type strains of phylogenetically related taxa. The DNA G+C content of strain AH-MY3T was 37 mol%. The phylogenetic data and differential chemotaxonomic and other phenotypic properties revealed that strain AH-MY3T represents a novel genus and species within the family Flavobacteriaceae, for which the name Aestuariivivens insulae gen. nov., sp. nov. is proposed. The type strain of Aestuariivivens insulae is AH-MY3T ( = KCTC 42350T = NBRC 110723T).