Cell Plasticity and Genomic Structure of a Novel Filterable Rhizobiales Bacterium that Belongs to a Widely Distributed Lineage

Deciphering the roles of nitrogen source in sharping synchronous metabolic pathways of linear alkylbenzene sulfonate and nitrogen in a membrane biofilm for treating greywater

Nitrogen (N) source is an important factor affecting biological wastewater treatment. Although the oxygen-based membrane biofilm showed excellent greywater treatment performance, how N source impacts the synchronous removal of organics and N is still unclear. In this work, how N species (urea, nitrate and ammonia) affect synchronous metabolic pathways of organics and N were evaluated during greywater treatment in the membrane biofilm. Urea and ammonia achieved efficient chemical oxygen demand (>97.5%) and linear alkylbenzene sulfonate (LAS, >98.5%) removal, but nitrate enabled the maximum total N removal (80.8 ± 2.6%). The nitrate-added system had poor LAS removal ratio and high residual LAS, promoting the accumulation of effluent protein-like organics and fulvic acid matter. N source significantly induced bacterial community succession, and the increasing of corresponded functional flora can promote the transformation and utilization of microbial-mediated N. The nitrate system was more conducive to the accumulation of denitrification related microorganisms and enzymes, enabling the efficient N removal. Combining with high amount of ammonia monooxygenase that contributing to LAS and N co-metabolism, LAS mineralization related microbes and functional enzymes were generously accumulated in the urea and ammonia systems, which achieved the high efficiency of organics and LAS removal.

Roseiterribacter gracilis gen. nov., sp. nov., a novel filterable alphaproteobacterium isolated from soil using a gel-filled microwell array device

Our previous studies indicate the abundant and diverse presence of yet-to-be-cultured microorganisms in the micropore-filtered fractions of various environmental samples. Here, we isolated a novel bacterium (designated as strain TMPK1T) from a 0.45-μm-filtered soil suspension by using a gel-filled microwell array device comprising 900 microwells and characterized its phylogenetic and physiological features. This strain showed low 16S rRNA gene sequence identities (<91%) and low average nucleotide identity values (<70%) to the closest validly described species, and belonged to a novel-family-level lineage within the order Rhodospirillales of Alphaproteobacteria. Strain TMPK1T exhibited small cell sizes (0.08-0.23 μm3) and had a high cyclopropane fatty acid content (>13%), and these characteristics were differentiated from other Rhodospirillales bacteria. A comprehensive habitability search using amplicon datasets suggested that TMPK1T and its close relatives are mainly distributed in soil and plant-associated environments. Based on these results, we propose that strain TMPK1T represents a novel genus and species named Roseiterribacter gracilis gen. nov., sp. nov. (JCM 34627T = KCTC 82790T). We also propose Roseiterribacteraceae fam. nov. to accommodate the genus Roseiterribacter.

Characterization of the First Cultured Psychrotolerant Representative of Legionella from Antarctica Reveals Its Unique Genome Structure

Culture-independent analysis shows that Legionella spp. inhabit a wide range of low-temperature environments, but to date, no psychrotolerant or psychrophilic strains have been reported. Here, we characterized the first cultivated psychrotolerant representative, designated strain TUM19329T, isolated from an Antarctic lake using a polyphasic approach and comparative genomic analysis. A genome-wide phylogenetic tree indicated that this strain was phylogenetically separate at the species level. Strain TUM19329T shared common physiological traits (e.g., Gram-negative, limited growth on buffered charcoal-yeast extract α-ketoglutarate [BCYEα] agar with l-cysteine requirements) with its relatives, but it also showed psychrotolerant growth properties (e.g., growth at 4°C to 25°C). Moreover, this strain altered its own cellular fatty acid composition to accumulate unsaturated fatty acid at a lower temperature, which may help maintain the cell membrane fluidity. Through comparative genomic analysis, we found that this strain possessed massive mobile genetic elements compared with other species, amounting to up to 17% of the total genes. The majority of the elements were the result of the spread of only a few insertion sequences (ISs), which were spread throughout the genome by a "copy-and-paste" mechanism. Furthermore, we found metabolic genes, such as fatty acid synthesis-related genes, acquired by horizontal gene transfer (HGT). The expansion of ISs and HGT events may play a major role in shaping the phenotype and physiology of this strain. On the basis of the features presented here, we propose a new species-Legionella antarctica sp. nov.-represented by strain TUM19329T (= GTC 22699T = NCTC 14581T). IMPORTANCE This study characterized a unique cultivated representative of the genus Legionella isolated from an Antarctic lake. This psychrotolerant strain had some common properties of known Legionella species but also displayed other characteristics, such as plasticity in fatty acid composition and an enrichment of mobile genes in the genome. These remarkable properties, as well as other factors, may contribute to cold hardiness, and this first cultivated cold-tolerant strain of the genus Legionella may serve as a model bacterium for further studies. It is worth noting that environmentally derived 16S rRNA gene phylotypes closely related to the strain characterized here have been detected from diverse environments outside Antarctica, suggesting a wide distribution of psychrotolerant Legionella bacteria. Our culture- and genome-based findings may accelerate the ongoing studies of the behavior and pathogenicity of Legionella spp., which have been monitored for many years in the context of public health.

Characterization of Terrihabitans soli gen. nov., sp. nov., a Novel 0.2 μm-Filterable Soil Bacterium Belonging to a Widely Distributed Lineage of Hyphomicrobiales (Rhizobiales)

We previously showed that novel filterable bacteria remain in “sterile” (<0.2 μm filtered) terrestrial environmental samples from Japan, China, and Arctic Norway. Here, we characterized the novel filterable strain IZ6T, a representative strain of a widely distributed lineage. Phylogenetic analysis showed that this strain was affiliated with the Rhizobiales (now proposed as Hyphomicrobiales) of Alphaproteobacteria, but distinct from any other type strains. Strain IZ6T shared the following chemotaxonomic features with the closest (but distantly) related type strain, Flaviflagellibacter deserti SYSU D60017T: ubiquinone-10 as the major quinone; phosphatidylethanolamine, phosphatidylcholine, and phosphatidylglycerol as major polar lipids; and slightly high G+C content of 62.2 mol%. However, the cellular fatty acid composition differed between them, and the unsaturated fatty acid (C18:1ω7c/C18:1ω6c) was predominantly found in our strain. Moreover, unlike methyrotrophs and nitrogen-fixers of the neighboring genera of Hyphomicrobiales (Rhizobiales), strain IZ6T cannot utilize a one-carbon compound (e.g., methanol) and fix atmospheric nitrogen gas. These findings were consistent with the genome-inferred physiological potential. Based on the phylogenetic, physiological, and chemotaxonomic traits, we propose that strain IZ6T represents a novel genus and species with the name Terrihabitans soli gen. nov., sp. nov. (=NBRC 106741T = NCIMB 15058T). The findings will provide deeper insight into the eco-physiology of filterable microorganisms.