Xuesong Luo

Salinization is considered a threat to agricultural soil and decreases crop yield worldwide. Nitrification and denitrification are the core processes of soil N-cycle. However, the response of nitrifiers and denitrifiers to salinity in agricultural soils remains ambiguous. The study aimed to explore the effect of salinity on nitrifiers and denitrifiers communities in agricultural soils along a naturally occurring salinity gradient. The effects of salinity on the abundance, composition, and interactions of nitrifiers and denitrifiers in surface soils were investigated. The abundance of nitrifiers significantly decreased in response to the increase in salinity. Ammonia-oxidizing archaea (AOA) were more susceptible to salinity elevation than ammonia-oxidizing bacteria (AOB). Nitrospira and Nitrobacter showed a similar trend to the salinity gradient, but the relative abundance of Nitrobacter was increased in the saline soils. High salinity decreased the abundance of napA and nirK, but had no significant effect on other marker genes for denitrification. Besides electrical conductivity, total sulfur (TS)+available potassium (AK) and TN+TS+C/N+total phosphorus (TP)+AK significantly explained the variation in denitrifier and nitrifier communities. We also found that high salinity decreased the connections between different N functional genes. These results implied the alteration of the nitrogen cycling community by high salinity mainly through decreasing AOA, NOB, and some denitrifiers with nitrate or nitrite reduction potentials and weakening the connectivity between nitrogen cycling drivers.

Vibrio parahaemolyticus V110 is a marine origin pathogen infecting shrimp. Its resistance to oxidative stress is important for its survival in the complex marine ecosystems. vpa0768 (katG1) and vpa0453 (katG2) were previously found to contribute to the resistance against H₂O₂ and isopropylbenzene. Our data showed that purified KatG2 and KatG1 possessed similar activity for hydrolyzing H₂O₂ at 37 °C. The transcription of katG genes was induced by H₂O₂, cumene, and tert‐butyl hydroperoxide (TBHP). The fold change of katG2 transcripts induced by isopropylbenzene was significantly higher than that of katG1. oxyR and rpoS are well‐known regulatory genes which control the anti‐oxidative and general stress response pathways, respectively. Deletion of rpoS resulted pathways, respectively. Deletion of rpoS resulted in abolishing the induction of katGs by the peroxides, and oxyR deletion only weakened the expression of the two genes. These results indicate that the two katGs encoding active enzymes are both inducible, but differ in their inducer preference. RpoS and oxyR are required for the full expression of katGs, but other unknown sensing regulators could be involved in the oxidative stress response besides OxyR.

Few diazotrophs have been found to belong to the family Cytophagaceae so far. In the present study, a Gram-negative, rod-shaped bacterium that forms red colonies, was isolated from sands of the Takalamakan desert. It was designated H4X^T. Phylogenetic and biochemical analysis indicated that the isolate is a new species of the genus Pontibacter. The 16S rRNA gene of H4X^T displays 94.2–96.8% sequence similarities to those of other strains in Pontibacter. The major respiratory quinone is menaquinone-7 (MK-7). The DNA G+C content is 46.6 mol%. The major cellular fatty acids are iso-C_15∶0, C_16∶1ω5c, summed feature 3 (containing C_16∶1ω6c and/or C_16∶1ω7c) and summed feature 4 (comprising anteiso-C_17∶1B and/or iso-C_17∶1I). The major polar lipids are phosphatidylethanolamine (PE), one aminophospholipid (APL) and some unknown phospholipids (PLs). It is interesting to see that this bacterium can grow very well in a nitrogen-free medium. PCR amplification suggested that the bacterium possesses at least one type of nitrogenase gene. Acetylene reduction assay showed that H4X^T actually possesses nitrogen-fixing activity. Therefore, it can be concluded that H4X^T is a new diazotroph. We thus referred it to as Pontibacter diazotrophicus sp. nov. The type strain is H4X^T ( = CCTCC AB 2013049^T = NRRL B-59974^T).

So far, little is known about the diversity of the radiation‐resistant microbes of the hyperarid Taklimakan Desert. In this study, ionizing radiation (IR)‐resistant bacteria from two sites in Xinjiang were investigated. After exposing the arid (water content of 0.8 ± 0.3%) and non‐arid (water content of 21.3 ± 0.9%) sediment samples to IR of 3000 Gy using a ⁶⁰Co source, a total of 52 γ‐radiation‐resistant bacteria were isolated from the desert sample. The 16S rRNA genes of all isolates were sequenced. The phylogenetic tree places these isolates into five groups: Cytophaga–Flavobacterium–Bacteroides, Proteobacteria, Deinococcus‐Thermus, Firmicutes, and Actinobacteria. Interestingly, this is the first report of radiation‐resistant bacteria belonging to the genera Knoellia, Lysobacter, Nocardioides, Paracoccus, Pontibacter, Rufibacter and Microvirga. The 16s rRNA genes of four isolates showed low sequence similarities to those of the published species. Phenotypic analysis showed that all bacteria in this study are able to produce catalase, suggesting that these bacteria possess reactive oxygen species (ROS)‐scavenging enzymes. These radiation‐resistant bacteria also displayed diverse metabolic properties. Moreover, their radiation resistances were found to differ. The diversity of the radiation‐resistant bacteria in the desert provides further ecological support for the hypothesis that the ionizing‐radiation resistance phenotype is a consequence of the evolution of ROS‐scavenging systems that protect cells against oxidative damage caused by desiccation.

A novel golden-yellow-coloured strain, designated RHYL-37T, was isolated from a soil sample from a forest of Euphrates poplar (Populus euphratica) in Xinjiang, China. The cells were strictly aerobic, Gram-staining-negative, heterotrophic, non-spore-forming rods that were motile by gliding. Growth occurred at 17–37 °C (optimum, 30 °C), at pH 5.0–9.0 (optimum, pH 7.0) and with 0–1 % NaCl (w/v; optimum, 0 %). Phylogenetic analysis based on 16S rRNA gene sequences indicated that the novel isolate formed a cluster with members of the genera Segetibacter, Terrimonas, Niastella, Niabella and Chitinophaga in the family ‘Chitinophagaceae’ in the phylum Bacteroidetes. Sequence similarities with the type strains of recognized species ranged from 90.6 to 94.0 %. The predominant isoprenoid quinone was MK-7 and the major cellular fatty acids were iso-C15 : 0, iso-C15 : 1, C16 : 0 and iso-C17 : 0 3-OH. The DNA G+C content was 39.7 mol%. On the basis of the phylogenetic, physiological and chemotaxonomic data, strain RHYL-37T represents a novel genus and species in the family ‘Chitinophagaceae’, for which the name Parasegetibacter luojiensis gen. nov., sp. nov. is proposed. The type strain of Parasegetibacter luojiensis is RHYL-37T (=CCTCC AB 208240T=KCTC 22561T).