Complete biodegradation of tetrabromobisphenol A through sequential anaerobic reductive dehalogenation and aerobic oxidation.

Tetrabromobisphenol A (TBBPA), a common brominated flame retardant and a notorious pollutant in anaerobic environments, resists aerobic degradation but can undergo reductive dehalogenation to produce bisphenol A (BPA), an endocrine disruptor. Conversely, BPA is resistant to anaerobic biodegradation but susceptible to aerobic degradation. Microbial degradation of TBBPA via anoxic/oxic processes is scarcely documented. We established an anaerobic microcosm for TBBPA dehalogenation to BPA facilitated by humin. Dehalobacter species increased with a growth yield of 1.5 × 108 cells per µmol Br- released, suggesting their role in TBBPA dehalogenation. We innovatively achieved complete and sustainable biodegradation of TBBPA in sand/soil columns columns, synergizing TBBPA reductive dehalogenation by anaerobic functional microbiota and BPA aerobic oxidation by Sphingomonas sp. strain TTNP3. Over 42 days, 95.11 % of the injected TBBPA in three batches was debrominated to BPA. Following injection of strain TTNP3 cells, 85.57 % of BPA was aerobically degraded. Aerobic BPA degradation column experiments also indicated that aeration and cell colonization significantly increased degradation rates. This treatment strategy provides valuable technical insights for complete TBBPA biodegradation and analogous contaminants.

Sphingomonas lacusdianchii sp. nov., an attached bacterium inhibited by metabolites from its symbiotic cyanobacterium.

An alpha-proteobacterial strain JXJ CY 53 T was isolated from the cyanosphere of Microcystis sp. FACHB-905 (MF-905) collected from Lake Dianchi, China. JXJ CY 53 T was observed to be an aerobic, Gram-stain-negative, oval shaped, and mucus-secreting bacterium. It had C18:1ω7c and C16:0 as the major cellular fatty acids, Q-10 as the predominant ubiquinone, and sphingoglycolipid, diphosphatidylglycerol, phosphatidylcholine, and phosphatidylmethylethanolamine as the polar lipids. The G + C content of DNA was 65.85%. The bacterium had 16S rRNA gene sequence identities of 98.9% and 98.7% with Sphingomonas panni DSM 15761 T and Sphingomonas hankookensis KCTC 22579 T, respectively, while less than 97.4% identities with other members of the genus. Further taxonomic analysis indicated that JXJ CY 53 T represented a new member of Sphingomonas, and the species epithet was proposed as Sphingomonas lacusdianchii sp. nov. (type strain JXJ CY 53 T = KCTC 72813 T = CGMCC 1.17657 T). JXJ CY 53 T promoted the growth of MF-905 by providing bio-available phosphorus and nitrogen, plant hormones, vitamins, and carotenoids. It could modulate the relative abundances of nonculturable bacteria associated with MF-905 and influence the interactions of MF-905 and other bacteria isolated from the cyanobacterium, in addition to microcystin production characteristics. Meanwhile, MF-905 could provide JXJ CY 53 T dissolved organic carbon for growth, and control the growth of JXJ CY 53 T by secreting specific chemicals other than microcystins. Overall, these results suggest that the interactions between Microcystis and its attached bacteria are complex and dynamic, and may influence the growth characteristics of the cyanobacterium. This study provided new ideas to understand the interactions between Microcystis and its attached bacteria. KEY POINTS: • A novel bacterium (JXJCY 53 T) was isolated from the cyanosphere of Microcystis sp. FACHB-905 (MF-905) • JXJCY 53 T modulated the growth and microcystin production of MF-905 • MF-905 could control the attached bacteria by specific chemicals other than microcystins (MCs).

Mutagenesis enhances gellan gum production by a novel Sphingomonas spp: upstream optimization, kinetic modeling, and structural and physico-functional evaluation / La mutagénesis mejora la producción de goma gellan mediante una nueva especie de Sphingomonas: optimización ascendente, modelado cinético y evaluación estructural y físico-funcional

Gellan gum (GG) has gained tremendous attention owing to its diversified applications. However, its high production and hence market cost are still a bottleneck in its widespread utilization. In the present study, high GG producing mutant of Sphingomonas spp. was developed by random mutagenesis using ethyl methylsulphonate (EMS) for industrial fermentation and identified as Sphingomonas trueperi after 16S rRNA and matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF–MS) analysis. The fermentation conditions such as pH, temperature, and inoculum ratio were optimized by one factor at a time (OFAT) followed by screening of medium components by the Plackett–Burman statistical design. The most critical nutrients were further optimized by response surface methodology for maximizing GG production. The effect of dissolved oxygen tension in bioreactor on cell growth, substrate consumption, GG production, and batch productivity was elucidated. The highest GG titer (23 ± 2.4 g/L) was attained in optimized medium at 10% inoculum (6.45 ± 0.5 log cfu/mL) under controlled fermentation conditions of pH (7), temperature (30 °C), agitation (300–600 rpm), and aeration (0.5–2.0 SLPM) at 22 ± 2% dissolved oxygen tension in a 10-L bioreactor. Kinetic modeling of optimized batch process revealed that logistic growth model could best explain biomass accumulation, while GG formation and substrate consumption were best explained by Luedeking-Piret and exponential decay model, respectively. Structural and physico-functional features of GG produced by mutant Sphingomonas spp. were characterized by HPLC, FTIR, NMR, DSC, TGA, GPC, SEM, and rheological analysis. The higher productivity (0.51 g/L/h) under optimized fermentation conditions suggests potential consideration of mutant and process for commercial utilization.(AU)

Sphingomonas flavescens sp. nov., isolated from soil.

An aerobic bacterium, designated as PT-12T, was isolated from soil collected from agriculture field, and its taxonomic position was validated through a comprehensive polyphasic methodology. The strain was identified as Gram-stain-negative, non-motile, rod-shaped, and catalase- and oxidase-positive. The yellow-colored colonies showed growth ability at temperature range of 18-37 °C, NaCl content of 0-1.0% (w/v), and at a pH of 6.0-8.0. The 16S rRNA gene and phylogenetic analysis showed that strain PT-12T affiliated with the genus Sphingomonas in the family Sphingomonadaceae, and displayed the highest 16S rRNA nucleotide sequence similarity with Sphingomonas limnosediminicola 03SUJ6T (98.4%). The genome size of strain PT-12T was 2,656,862 bp and the DNA G + C content estimated from genome was 63.5%. The highest values of average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) were observed between strain PT-12T and Sphingomonas segetis YJ09T, accounting to 76.2% and 20.2%, respectively. In addition, both ANI and dDDH values between strain PT-12T and other phylogenetically related neighbors ranged between 69.6% and 76.2% and 18.4% and 20.2%, respectively. Chemotaxonomic features exhibited Q-10 as the only ubiquinone; homospermidine as the major polyamine; summed feature 8 (C18:1ω7c and/or C18:1ω6c), C16:0, and 10-methyl C18:0 as the notable fatty acids; and phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, phosphatidylcholine, and sphingoglycolipid as dominating polar lipids. Overall, the comprehensive polyphasic data supported that strain PT-12T represents a novel bacterial species within the genus Sphingomonas. Accordingly, we propose the name Sphingomonas flavescens sp. nov. The type strain is PT-12T (= KCTC 92114T = NBRC 115717T).

Metagenomic and proteomic insights into the self-adaptive cell surface hydrophobicity of Sphingomonas sp. strain PAH02 reducing the migration of cadmium-phenanthrene co-pollutant in rice.

Cell surface hydrophobicity (CSH) dominates the interactions between rhizobacteria and pollutants at the soil-water interface, which is critical for understanding the dissipation of pollutants in the rhizosphere microzone of rice. Herein, we explored the effects of self-adaptive CSH of Sphingomonas sp. strain PAH02 on the translocation and biotransformation behaviour of cadmium-phenanthrene (Cd-Phe) co-pollutant in rice and rhizosphere microbiome. We evidenced that strain PAH02 reduced the adsorption of Cd-Phe co-pollutant on the rice root surface while enhancing the degradation of Phe and adsorption of Cd via its self-adaptive CSH in the hydroponic experiment. The significant upregulation of key protein expression levels such as MerR, ARHDs and enoyl-CoA hydratase/isomerase, ensures self-adaptive CSH to cope with the stress of Cd-Phe co-pollutant. Consistently, the bioaugmentation of strain PAH02 promoted the formation of core microbiota in the rhizosphere soil of rice (Oryza sativa L.), such as Bradyrhizobium and Streptomyces and induced gene enrichment of CusA and PobA that are strongly associated with pollutant transformation. Consequently, the contents of Cd and Phe in rice grains at maturity decreased by 17.2% ± 0.2% and 65.7% ± 0.3%, respectively, after the bioaugmentation of strain PAH02. These findings present new opportunities for the implementation of rhizosphere bioremediation strategies of co-contaminants in paddy fields.

sRNA molecules participate in hyperosmotic stress response regulation in Sphingomonas melonis TY.

Drought and salinity are ubiquitous environmental factors that pose hyperosmotic threats to microorganisms and impair their efficiency in performing environmental functions. However, bacteria have developed various responses and regulatory systems to cope with these abiotic challenges. Posttranscriptional regulation plays vital roles in regulating gene expression and cellular homeostasis, as hyperosmotic stress conditions can lead to the induction of specific small RNA molecules (sRNAs) that participate in stress response regulation. Here, we report a candidate functional sRNA landscape of Sphingomonas melonis TY under hyperosmotic stress, and 18 sRNAs were found with a clear response to hyperosmotic stress. These findings will help in the comprehensive analysis of sRNA regulation in Sphingomonas species. Weighted correlation network analysis revealed a 263 nucleotide sRNA, SNC251, which was transcribed from its own promoter and showed the most significant correlation with hyperosmotic response factors. Deletion of snc251 affected biofilm formation and multiple cellular processes, including ribosome-related pathways, aromatic compound degradation, and the nicotine degradation capacity of S. melonis TY, while overexpression of SNC251 facilitated biofilm formation by TY under hyperosmotic stress. Two genes involved in the TonB system were further verified to be activated by SNC251, which also indicated that SNC251 is a trans-acting sRNA. Briefly, this research reports a landscape of sRNAs participating in the hyperosmotic stress response in S. melonis and reveals a novel sRNA, SNC251, which contributes to the S. melonis TY biofilm formation and thus enhances its hyperosmotic stress response ability.IMPORTANCESphingomonas species play a vital role in plant defense and pollutant degradation and survive extensively under drought or salinity. Previous studies have focused on the transcriptional and translational responses of Sphingomonas under hyperosmotic stress, but the posttranscriptional regulation of small RNA molecules (sRNAs) is also crucial for quickly modulating cellular processes to adapt dynamically to osmotic environments. In addition, the current knowledge of sRNAs in Sphingomonas is extremely scarce. This research revealed a novel sRNA landscape of Sphingomonas melonis and will greatly enhance our understanding of sRNAs' acting mechanisms in the hyperosmotic stress response.

The production of ultrahigh molecular weight xanthan gum from a Sphingomonas chassis capable of co-utilising glucose and xylose from corn straw.

Corn straw is an abundant and renewable alternative for microbial biopolymer production. In this paper, an engineered Sphingomonas sanxanigenens NXG-P916 capable of co-utilising glucose and xylose from corn straw total hydrolysate to produce xanthan gum was constructed. This strain was obtained by introducing the xanthan gum synthetic operon gum as a module into the genome of the constructed chassis strain NXdPE that could mass produce activated precursors of polysaccharide, and in which the transcriptional levels of gum genes were optimised by screening for a more appropriate promoter, P916 . As a result, strain NXG-P916 produced 9.48 ± 0.34 g of xanthan gum per kg of fermentation broth (g/kg) when glucose was used as a carbon source, which was 2.1 times improved over the original engineering strain NXdPE::gum. Furthermore, in batch fermentation, 12.72 ± 0.75 g/kg xanthan gum was produced from the corn straw total hydrolysate containing both glucose and xylose, and the producing xanthan gum showed an ultrahigh molecular weight (UHMW) of 6.04 × 107 Da, which was increased by 15.8 times. Therefore, the great potential of producing UHMW xanthan gum by Sphingomonas sanxanigenens was proved, and the chassis NXdPE has the prospect of becoming an attractive platform organism producing polysaccharides derived from biomass hydrolysates.

NMR analysis of the side-group substituents in welan gum in comparison to gellan gum.

The physicochemical properties and applications of polysaccharides are highly dependent on their chemical structures, including the monosaccharide composition, degree of substitution, and position of substituent groups in the backbone. The occurrence of side groups or side chains in the chain backbone of polysaccharides is often an essential factor influencing their conformational and physicochemical properties. Welan gum produced by the fermentation of Sphingomonas sp. ATCC 31555 microorganisms has been widely used in food, construction, and oil drilling fields. While understanding the physicochemical properties of welan gum solution has been highly developed, there is still little information about the determination strategy of the glycosyl side groups in welan gum. In this study, the NMR method was established to quantitatively determine the substituent groups in the chain backbone of welan gum. The delicate chemical structures of welan gum obtained at different fermentation conditions were clarified. The composition and content of side substituents were also identified by high-performance liquid chromatography to confirm the accuracy of NMR analysis. The quantitative determination of substituent groups in gellan gum based on NMR analysis was also elaborated for comparison. This work provides insights for profoundly understanding the structure-function relationship of welan gum.

Structural conservation in the glutathione binding in Sphingomonas sp. glutaredoxin Grx3 and variations for cold adaptation.

Glutaredoxin 3 (Grx3), a redox protein with a thioredoxin-fold structure, maintains structural integrity and glutathione (GSH) binding capabilities across varying habitat temperatures. The cis-Pro loop, essential for GSH binding, relies on the Arg-Asp salt bridge (α2-α3) and Gln-His hydrogen bond (ß3-ß4) for its conformation. In some psychrophilic Grx3 variants, Arg in α2 is replaced with Tyr, and His in ß4 is replaced with Phe. This study examines the roles of these bonds in Grx3's structure, function, and cold adaptation, using SpGrx3 from the Arctic bacterium Sphingomonas sp. Despite its cold habitat, SpGrx3 maintains the Arg51-Asp69 salt bridge and Gln56-His63 hydrogen bond. The R51Y substitution disrupts the α2-α3 salt bridge, while the H63F and H63Y substitutions hinder the salt bridge through cation-π interactions with Arg51, involving Phe63/Tyr63, thereby enhancing flexibility. Conversely, mutations that disrupt the hydrogen bond (Q56A, H63A, and H63F) reduce thermal stability. In the psychrophilic Grx3 configuration A48T/R51Y/H63F, a Thr48-Gln56 hydrogen bond stabilizes the cis-Pro loop, enhancing flexibility by disrupting both bonds. Furthermore, all mutants exhibit reduced α-helical content and catalytic efficiency. In summary, the highly conserved Arg51-Asp69 salt bridge and Gln56-His63 hydrogen bond are crucial for stabilizing the cis-Pro loop and catalytic activity in SpGrx3. His63 is favored as it avoids cation-π interactions with Arg51, unlike Phe63/Tyr63. Psychrophilic Grx3 variants have adapted to cold environments by reducing GSH binding and increasing structural flexibility. These findings deepen our understanding of the structural conservation in Grx3 for GSH binding and the critical alterations required for cold adaptation.

Multifaceted photoreceptor compositions in dual phototrophic systems - A genomic analysis.

For microbes and their hosts, sensing of external cues is essential for their survival. For example, in the case of plant associated microbes, the light absorbing pigment composition of the plant as well as the ambient light conditions determine the well-being of the microbe. In addition to light sensing, some microbes can utilize xanthorhodopsin based proton pumps and bacterial photosynthetic complexes that work in parallel for energy production. They are called dual phototrophic systems. Light sensing requirements in these type of systems are obviously demanding. In nature, the photosensing machinery follows mainly the same composition in all organisms. However, the specific role of each photosensor in specific light conditions is elusive. In this study, we provide an overall picture of photosensors present in dual phototrophic systems. We compare the genomes of the photosensor proteins from dual phototrophs to those from similar microbes with "single" phototrophicity or microbes without phototrophicity. We find that the dual phototrophic bacteria obtain a larger variety of photosensors than their light inactive counterparts. Their rich domain composition and functional repertoire remains similar across all microbial photosensors. Our study calls further investigations of this particular group of bacteria. This includes protein specific biophysical characterization in vitro, microbiological studies, as well as clarification of the ecological meaning of their host microbial interactions.

A novel UV-resistant bacterium Sphingomonas endolithica sp. nov., and genomic analysis, isolated from the north slope of Mount Everest.

Gram-stain-negative, aerobic, rod-shaped, non-motile bacterium strain ZFBP2030T was isolated from a rock on the North slope of Mount Everest. This strain contained a unique ubiquinone-10 (Q-10) as a predominant respiratory quinone. Among the tested fatty acids, the strain contained summed feature 8, C14:0 2OH, and C16:0, as major cellular fatty acids. The polar lipid profile contained phosphatidyl glycerol, phosphatidyl ethanolamine, three unidentified phospholipids, two unidentified aminolipids, and six unidentified lipids. The cell-wall peptidoglycan was a meso-diaminopimelic acid, and cell-wall sugars were ribose and galactose. Phylogenetic analyses based on 16S rRNA gene sequence revealed that strain ZFBP2030T was a member of the genus Sphingomonas, exhibiting high sequence similarity to the 16S rRNA gene sequences of Sphingomonas aliaeris DH-S5T (97.9%), Sphingomonas alpina DSM 22537T (97.3%) and Sphingomonas hylomeconis CCTCC AB 2013304T (97.0%). The 16S rRNA gene sequence similarity between ZFBP2030T and other typical strains was less than 97.0%. The average amino acid identity values, average nucleotide identity, and digital DNA-DNA hybridization values between strain ZFBP2030T and its highest sequence similarity strains were 56.9-79.9%, 65.1-82.2%, and 19.3-25.8%, respectively. The whole-genome size of the novel strain ZFBP2030T was 4.1 Mbp, annotated with 3838 protein-coding genes and 54 RNA genes. Moreover, DNA G + C content was 64.7 mol%. Stress-related functions predicted in the subsystem classification of the strain ZFBP2030T genome included osmotic, oxidative, cold/heat shock, detoxification, and periplasmic stress responses. The overall results of this study clearly showed that strain ZFBP2030T is a novel species of the genus Sphingomonas, for which the name Sphingomonas endolithica sp. nov. is proposed. The type of strain is ZFBP2030T (= EE 013T = GDMCC 1.3123T = JCM 35386T).

Foliar Spraying of Chlorpyrifos Triggers Plant Production of Linolenic Acid Recruiting Rhizosphere Bacterial Sphingomonas sp.

Plants have developed an adaptive strategy for coping with biotic or abiotic stress by recruiting specific microorganisms from the soil pool. Recent studies have shown that the foliar spraying of pesticides causes oxidative stress in plants and leads to changes in the rhizosphere microbiota, but the mechanisms by which these microbiota change and rebuild remain unclear. Herein, we provide for the first-time concrete evidence that rice plants respond to the stress of application of the insecticide chlorpyrifos (CP) by enhancing the release of amino acids, lipids, and nucleotides in root exudates, leading to a shift in rhizosphere bacterial community composition and a strong enrichment of the genus Sphingomonas sp. In order to investigate the underlying mechanisms, we isolated a Sphingomonas representative isolate and demonstrated that it is both attracted by and able to consume linolenic acid, one of the root exudates overproduced after pesticide application. We further show that this strain selectively colonizes roots of treated plants and alleviates pesticide stress by degrading CP and releasing plant-beneficial metabolites. These results indicate a feedback loop between plants and their associated microbiota allowing to respond to pesticide-induced stress.

Unraveling the roles of aromatic cluster side-chain interactions on the structural stability and functional significance of psychrophilic Sphingomonas sp. glutaredoxin 3.

This study investigates the impact of aromatic cluster side-chain interactions in Grx3 (SpGrx3) from the psychrophilic Arctic bacterium Sphingomonas sp. Grx3 is a class I oxidoreductase with a unique parallel arrangement of aromatic residues in its aromatic cluster, unlike the tetrahedral geometry observed in Trxs. Hydrophilic-to-hydrophobic substitutions were made in the aromatic cluster, in ß1 (E5V and Y7F), adjacent ß2 (Y32F and Y32L), both ß1 and ß2 (E5V/Y32L), and short α2 (R47F). The hydrophobic substitutions, particularly those at or near Tyr7 (E5V, Y7F, Y32F, and R47F), increased melting temperatures and conformational stability, whereas disrupting ß1-ß2 interactions (Y32L and E5V/Y32L) led to structural instability of SpGrx3. However, excessive hydrophobic interactions (Y7F and E5V/Y32L) caused protein aggregation at elevated temperatures. All mutations resulted in a reduction in α-helical content and an increase in ß-strand content. The R47F mutant, which formed dimers and exhibited the highest ß-strand content, showed increased conformational flexibility and a significant decrease in catalytic rate due to the disturbance of ß1-α2 interactions. In summary, the configuration of the aromatic cluster, especially Tyr7 in the buried ß1 and Arg47 in the short α2, played crucial roles in maintaining the active conformation of SpGrx3 and preventing its protein aggregation. These modifications, reducing hydrophobicity in the central ß-sheet, distinguish Grx3 from other Trx-fold proteins, highlighting evolutionary divergence within the Trx-fold superfamily and its functional versatility.

Sphingomonas abietis sp. nov., an Endophytic Bacterium Isolated from Korean Fir.

PAMB 00755T, a bacterial strain, was isolated from Korean fir leaves. The strain exhibits yellow colonies and consists of Gram-negative, non-motile, short rods or ovoid-shaped cells. It displays optimal growth conditions at 20°C, 0% NaCl, and pH 6.0. Results of 16S rRNA gene-based phylogenetic analyses showed that strain PAMB 00755T was most closely related to Sphingomonas chungangi MAH-6T (97.7%) and Sphingomonas polyaromaticivorans B2-7T (97.4%), and ≤96.5% sequence similarity to other members of the genus Sphingomonas. The values of average nucleotide identity (79.9-81.3%), average amino acid identity (73.3-75.9%), and digital DNA-DNA hybridization (73.3-75.9%) were significantly lower than the threshold values for species boundaries; these overall genome-related indexes (OGRI) analyses indicated that the strain represents a novel species. Genomic analysis revealed that the strain has a 4.4-Mbp genome encoding 4,083 functional genes, while the DNA G+C content of the whole genome is 66.1%. The genome of strain PAMB 00755T showed a putative carotenoid biosynthetic cluster responsible for its antioxidant activity. The respiratory quinone was identified as ubiquinone 10 (Q-10), while the major fatty acids in the profile were identified as C18:1ω7c and/or C18:1ω6c (summed feature 8). The major polar lipids of strain PAMB 00755T were diphosphatidylglycerol, phosphatidylethanolamine, sphingoglycolipid, and phosphatidylcholine. Based on a comprehensive analysis of genomic, phenotypic, and chemotaxonomic characteristics, we proposed the name Sphingomonas abietis sp. nov. for this novel species, with PAMB 00755T as the type strain (= KCTC 92781T = GDMCC 1.3779T).

Characterization of Hsp17, a Novel Small Heat Shock Protein, in Sphingomonas melonis TY under Heat Stress.

Bacteria are constantly exposed to a variety of environmental stresses. Temperature is considered one of the most important environmental factors affecting microbial growth and survival. As ubiquitous environmental microorganisms, Sphingomonas species play essential roles in the biodegradation of organic contaminants, plant protection, and environmental remediation. Understanding the mechanism by which they respond to heat shock will help further improve cell resistance by applying synthetic biological strategies. Here, we assessed the transcriptomic and proteomic responses of Sphingomonas melonis TY to heat shock and found that stressful conditions caused significant changes in functional genes related to protein synthesis at the transcriptional level. The most notable changes observed were increases in the transcription (1,857-fold) and protein expression (11-fold) of Hsp17, which belongs to the small heat shock protein family, and the function of Hsp17 in heat stress was further investigated in this study. We found that the deletion of hsp17 reduced the capacity of the cells to tolerate high temperatures, whereas the overexpression of hsp17 significantly enhanced the ability of the cells to withstand high temperatures. Moreover, the heterologous expression of hsp17 in Escherichia coli DH5α conferred to the bacterium the ability to resist heat stress. Interestingly, its cells were elongated and formed connected cells following the increase in temperature, while hsp17 overexpression restored their normal morphology under high temperature. In general, these results indicate that the novel small heat shock protein Hsp17 greatly contributes to maintaining cell viability and morphology under stress conditions. IMPORTANCE Temperature is generally considered the most important factor affecting metabolic functions and the survival of microbes. As molecular chaperones, small heat shock proteins can prevent damaged protein aggregation during abiotic stress, especially heat stress. Sphingomonas species are widely distributed in nature, and they can frequently be found in various extreme environments. However, the role of small heat shock proteins in Sphingomonas under high-temperature stress has not been elucidated. This study greatly enhances our understanding of a novel identified protein, Hsp17, in S. melonis TY in terms of its ability to resist heat stress and maintain cell morphology under high temperature, leading to a broader understanding of how microbes adapt to environmental extremes. Furthermore, our study will provide potential heat resistance elements for further enhancing cellular resistance as well as the synthetic biological applications of Sphingomonas.

Isolation and Characterization of Sphingomonas telluris, Sphingomonas caseinilyticus Isolated from Wet Land Soil.

Two novel bacterial strains, designated as SM33T and NSE70-1T, were isolated from wet soil in South Korea. To get the taxonomic positions, the strains were characterized. The genomic information (both 16S rRNA gene and draft genome sequence analysis) show that both novel isolates (SM33T and NSE70-1T) belong to the genus Sphingomonas. SM33T share the highest 16s rRNA gene similarity (98.2%) with Sphingomonas sediminicola Dae20T. In addition, NSE70-1T show 96.4% 16s rRNA gene similarity with Sphingomonas flava THG-MM5T. The draft genome of strains SM33T and NSE70-1T consist of a circular chromosome of 3,033,485 and 2,778,408 base pairs with DNA G+C content of 63.9, and 62.5%, respectively. Strains SM33T and NSE70-1T possessed the ubiquinone Q-10 as the major quinone, and a fatty acid profile with C16:0, C18:1 2-OH, C16:1 ω7c/C16:1 ω6c (summed feature 3) and C18:1 ω7c/C18:1 ω6c (summed feature 8) as major fatty acids. The major polar lipids of SM33T and NSE70-1T were phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine, sphingoglycolipid and phosphatidylcholine, respectively. Moreover, genomic, physiological, and biochemical results allowed the phenotypic and genotypic differentiation of strains SM33T and NSE70-1T from their closest and other species of the genus Sphingomonas with validly published names. Therefore, the SM33T and NSE70-1T represent novel species of the genus Sphingomonas, for which the name Sphingomonas telluris sp. nov. (type strain SM33T = KACC 22222T = LMG 32193T), and Sphingomonas caseinilyticus (type strain NSE70-1T = KACC 22411T = LMG 32495T).

Sphingomonas caeni sp. nov., a phenolic acid-degrading bacterium isolated from activated sludge.

A Gram-stain-negative, rod-shaped, polar flagellated or stalked and non-spore-forming bacterium, designated LB-2T, was isolated from activated sludge. Growth was observed at 20-30 °C (optimum 28 °C), pH 6.0-8.0 (optimum pH 7.0) and salinity of 0-0.5% (w/v; optimum 0.5%). Phylogenetic analysis based on the 16S rRNA gene indicated that strain LB-2T belongs to the genus Sphingomonas and showed the highest sequence similarity (96.7%) and less than 96.7% similarities to other type strains. The genome size of strain LB-2T was 4.10 Mb, with 66.8 mol% G + C content. The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between strains LB-2T and S. canadensis FWC47T were 77.8% and 21%, respectively. The predominant cellular fatty acids were summed feature 8 (C18:1ω7c and/or C18 : 1ω6c) and C16:0. The major polar lipids were aminolipid, glycolipid, sphingoglycolipid, phosphatidylcholine, phosphatidylglycerol, four unidentified lipids, glycophospholipid, phosphatidylethanolamine and diphosphatidylglycerol. The predominant respiratory quinone was Q-10 and the major polyamine was sym-homospermidine. On the basis of phenotypic, genotypic and phylogenetic evidences, strain LB-2T represents a novel species in the genus Sphingomonas, for which the name Sphingomonas caeni sp. nov. is proposed. The type strain is LB-2T (GDMCC 1.3630T = NBRC 115,102T).

Characterization of four novel bacterial species of the genus Sphingomonas, Sphingomonas anseongensis, Sphingomonas alba, Sphingomonas brevis and Sphingomonas hankyongi sp.nov., isolated from wet land.

Four novel bacterial strains, designated as RG327T, SE158T, RB56-2T and SE220T, were isolated from wet soil in the Republic of Korea. To determine their taxonomic positions, the strains were fully characterized. On the basis of genomic information (16S rRNA gene and draft genome sequences), all four isolates represent members of the genus Sphingomonas. The draft genomes of RG327T, SE158T, RB56-2T and SE220T consisted of circular chromosomes of 2 226 119, 2 507 338, 2 593 639 and 2 548 888 base pairs with DNA G+C contents of 64.6, 63.6, 63.0 and 63.1 %, respectively. All the isolates contained ubiquinone Q-10 as the predominant quinone compound and a fatty acid profile with C16 : 0, C17 : 1ω6c, C18 : 1 2-OH, summed feature 3 (C16 : 1ω7c/C16 : 1ω6c) and summed feature 8 (C18 : 1ω7c/C18 : 1ω6c) as the major fatty acids, supporting the affiliation of strains RG327T, SE158T, RB56-2T and SE220T to the genus Sphingomonas. The major identified polar lipids in all four novel isolates were phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine, sphingoglycolipid and phosphatidylcholine. Moreover, the physiological, biochemical results and low level of DNA-DNA relatedness and average nucleotide identity values allowed the phenotypic and genotypic differentiation of RG327T, SE158T, RB56-2T and SE220T from other species of the genus Sphingomonas with validly published names and indicated that they represented novel species of the genus Sphingomonas, for which the names Sphingomonas anseongensis sp. nov. (RG327T = KACC 22409T = LMG 32497T), Sphingomonas alba sp. nov. (SE158T = KACC 224408T = LMG 324498T), Sphingomonas brevis (RB56-2T = KACC 22410T = LMG 32496T) and Sphingomonas hankyongi sp. nov., (SE220T = KACC 22406T = LMG 32499T) are proposed.

Biosynthesis and physicochemical properties of low molecular weight gellan produced by a high-yield mutant of Sphingomonas paucimobilis ATCC 31461.

Gellan gum (GG) is used in many industries. Here, we obtained a low molecular weight GG (L-GG) directly produced by M155, the high-yield mutant strain of Sphingomonas paucimobilis ATCC 31461, which was selected using UV-ARTP combined mutagenesis. The molecular weight of L-GG was 44.6 % lesser than that of the initial GG (I-GG), and the GG yield increased by 24 %. The monosaccharide composition and Fourier transform-infrared spectroscopic patterns of L-GG were similar to those of I-GG, which indicated that the decrease in the molecular weight of L-GG was probably because of reduction in the degree of polymerization. In addition, microstructural analysis revealed that the surface of L-GG was rougher, with smaller pores and tighter network, than that of I-GG. L-GG showed low hardness, gumminess, and chewiness, which are indicative of better taste. The results of rheological analysis revealed that the L-GG solution is a typical non-Newtonian fluid with low viscoelasticity, which exhibited stable dynamic viscoelasticity within 20-65 °C. To the best of our knowledge, this is the first report of direct biosynthesis of low molecular weight GG during fermentation, which will reduce the manufacturing costs. Our observations provide a reference for precise and expanded applications of GG.

Sphingomonas lycopersici sp. nov., isolated from tomato rhizosphere soil.

Two aerobic, Gram-stain-negative, non-motile and non-spore-forming rods bacterial strains, designated MMSM20T and MMSM24, were isolated from tomato rhizosphere soil and could produce indole-3-acetic acid and siderophore. Phylogenetic analyses based on 16S rRNA gene sequences and 92 core genes showed that strains MMSM20T and MMSM24 belonged to the genus Sphingomonas and were most closely related to three validly published species Sphingomonas jeddahensis G39T, Sphingomonas mucosissima DSM 17494T and Sphingomonas dokdonensis DSM 21029T. The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between strains MMSM20T and MMSM24 were 97.6 and 81.0 %, respectively, demonstrating that they were conspecific. The ANI and dDDH values between the two strains and the three type strains above were below the threshold values for species delimitation. The genomic DNA G+C contents of strains MMSM20T and MMSM24 were 66.6 and 66.4 mol%, respectively. The major fatty acids of the two strains were identified as C14 : 0 2OH, summed feature 8 (C18 : 1 ω7c and/or C18 : 1 ω6c); the predominant quinone was ubiquinone 10; the polar lipids comprised diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylcholine, sphingoglycolipid and unidentified lipids. Results of phenotypic and genotypic analyses supported that strains MMSM20T and MMSM24 represent a novel species of the genus Sphingomonas, for which the name Sphingomonas lycopersici sp. nov. is proposed. The type strain is MMSM20T (=GDMCC 1.3401T=JCM 35647T).