Acidicapsa dinghuensis sp. nov., a novel acidobacterium isolated from forest soil.

A bacterial strain, designated 4GSKXT, isolated from the forest soil of Dinghushan Biosphere Reserve, Guangdong Province, PR China (112° 31' E 23° 10' N), is proposed as a novel species of the genus Acidicapsa. Cells of strain 4GSKXT were aerobic, non-motile, Gram-stain-negative short rods that multiplied by binary division. The strain grew at 12-37 °C (optimum, 25-30 °C), pH 4.0-6.5 (optimum, pH 4.5-5.0) and NaCl concentrations of 0-1.0 % (w/v; optimum, 0 %). Strain 4GSKXT utilized various carbon sources as growth substrates, including both sugars and amino acids. The major fatty acids (>10 %) were iso-C15 : 0 (48.8 %) and iso-C17 : 1ω9c/C16 : 0 10-methyl (14.7 %). The major polar lipids were phosphatidylethanolamine, an unidentified glycolipid, three unidentified phospholipids and two unidentified aminophospholipids. The only quinone detected was MK-8 and the DNA G+C content was 52.8 mol%. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain 4GSKXT belongs to the genus Acidicapsa in the family Acidobacteriaceae in subdivision 1 of the phylum Acidobacteria, with the highest similarity of 97.1 % to Acidicapsa ligni WH120T. Based on all phenotypic, chemotaxonomic and phylogenetic data obtained, it is proposed as a novel species of genus Acidicapsa, for which the name Acidicapsa dinghuensis sp. nov. is proposed, with 4GSKXT (=CGMCC 1.15449T=LMG 29213T) as the type strain.

Edaphobacter flagellatus sp. nov. and Edaphobacter bradus sp. nov., two acidobacteria isolated from forest soil.

Two aerobic and obligately acidophilic bacteria, designated HZ411T and 4MSH08T, were isolated from the forest soil of Dinghushan Biosphere Reserve, Guangdong Province, PR China (23° 10' N, 112° 31' E). These two strains were Gram-stain-negative short rods that multiplied by binary division. HZ411T was motile, with a single polar flagellum, but 4MSH08T was non-motile. The results of the 16S rRNA gene sequence analysis indicated that these two strains formed a common clade with members of the genusEdaphobacterin subdivision 1 of the phylum Acidobacteria but they each occupied a unique position in the genus. HZ411T and 4MSH08T had a 16S rRNA gene sequence similarity of 96.2 % between each other and the highest sequence similarity of 97.7 and 96.9 % to Edaphobacter modestusJbg-1T and Edaphobacter aggregansWbg-1T, respectively. The DNA-DNA hybridization rate between HZ411T and E. modestusJbg-1T was 22.7 %. The DNA G+C contents of HZ411T and 4MSH08T were 57.7 and 59.3 %, respectively. HZ411T and 4MSH08T had similar major (>10 %) fatty acids with very high percentages of iso-C15 : 0 and C16 : 1ω7c, and similar major polar lipid profiles (both contained a phosphatidylethanolamine, phosphatidyldimethylethanolamine and glycolipid and several unidentified aminolipids and polar lipids). On the basis of these physiological, phylogenetic and chemotaxonomic data, we suggest that HZ411T and 4MSH08T represent two novel species of the genus Edaphobacter, for which the names Edaphobacter flagellatus HZ411T (=GDMCC 1.1193=LMG 30085) and Edaphobacter bradus 4MSH08T (=GDMCC 1.1317=KCTC 62475) are proposed.

Temporal heterogeneity of bacterial communities and their responses to Raphidiopsis raciborskii blooms.

To elucidate the interspecies connectivity between cyanobacteria and other bacteria (noncyanobacteria), microbial diversity and composition were investigated through high-throughput sequencing (HTS) in a drinking water reservoir in Chongqing city, Southwest China, during Raphidiopsis raciborskii blooms. Significant temporal changes were observed in microbial community composition during the sampling period, primarily reflected by variations in relative bacterial abundance. The modularity analysis of the network demonstrated that the bacterial community forms co-occurrence/exclusion patterns in response to variations in environmental factors. Moreover, five modules involved in the dynamic phases of the R. raciborskii bloom were categorized into the Pre-Bloom, Bloom, Post-Bloom, and Non-Bloom Groups. The reservoir was eutrophic (i.e., the average concentrations of total nitrogen (TN) and total phosphorus (TP) were 2.32 and 0.07 mg L-1, respectively) during the investigation; however, Pearson's correlation coefficient showed that R. raciborskii was not significantly correlated with nitrogen and phosphorus. However, other environmental factors, such as water temperature, pH, and the permanganate index, were positively correlated with R. raciborskii. Importantly, Proteobacteria (α-, γ-Proteobacteria), Acidobacteria, Chloroflexi, and Firmicutes were preferentially associated with increased R. raciborskii blooms. These results suggested that the transition of R. raciborskii bloom-related microbial modules and their keystone species could be crucial in the development and collapse of R. raciborskii blooms and could provide a fundamental basis for understanding the linkage between the structure and function of the microbial community during bloom dynamics.

Transcriptomic responses to phosphorus in an invasive cyanobacterium, Raphidiopsis raciborskii: Implications for nutrient management.

Phosphorus (P) is a vital macronutrient associated with the growth and proliferation of Raphidiopsis raciborskii, an invasive and notorious bloom-forming cyanobacterium. However, the molecular mechanisms involved in P acclimation remain largely unexplored for Raphidiopsis raciborskii. Here, transcriptome sequencing of Raphidiopsis raciborskii was conducted to reveal multifaceted mechanisms involved in mimicking dipotassium phosphate (DIP), ß-glycerol phosphate (Gly), 2-aminoethylphosphonic acid (AEP), and P-free conditions (NP). Chlorophyll a fluorescence parameters showed significant differences in the NP and AEP groups compared with the DIP and Gly-groups. Expression levels of genes related to phosphate transportation and uptake, organic P utilization, nitrogen metabolism, urea cycling, carbon fixation, amino acid metabolism, environmental information, the ATP-synthesis process in glycolysis, the tricarboxylic acid (TCA) cycle, and the pentose phosphate pathway were remarkably upregulated, while those related to photosynthesis, phycobiliproteins, respiration, oxidative phosphorylation, sulfur metabolism, and genetic information were markedly downregulated in the NP group relative to the DIP group. However, the expression of genes involved in organic P utilization, the urea cycle, and genetic information in the Gly-group, and carbon-phosphorus lyase, genetic information and environmental information in the AEP group were significantly increased compared to the DIP group. Together, these results indicate that Raphidiopsis raciborskii exhibits the evolution of coordination of multiple metabolic pathways and certain key genes to adapt to ambient P changes, which implies that if P is reduced to control Raphidiopsis raciborskii bloom, there is a risk that external nutrients (such as nitrogen, amino acids, and urea) will stimulate the growth or metabolism of Raphidiopsis.