The facilitating role of phycospheric heterotrophic bacteria in cyanobacterial phosphonate availability and Microcystis bloom maintenance.

BACKGROUND: Phosphonates are the main components in the global phosphorus redox cycle. Little is known about phosphonate metabolism in freshwater ecosystems, although rapid consumption of phosphonates has been observed frequently. Cyanobacteria are often the dominant primary producers in freshwaters; yet, only a few strains of cyanobacteria encode phosphonate-degrading (C-P lyase) gene clusters. The phycosphere is defined as the microenvironment in which extensive phytoplankton and heterotrophic bacteria interactions occur. It has been demonstrated that phytoplankton may recruit phycospheric bacteria based on their own needs. Therefore, the establishment of a phycospheric community rich in phosphonate-degrading-bacteria likely facilitates cyanobacterial proliferation, especially in waters with scarce phosphorus. We characterized the distribution of heterotrophic phosphonate-degrading bacteria in field Microcystis bloom samples and in laboratory cyanobacteria "phycospheres" by qPCR and metagenomic analyses. The role of phosphonate-degrading phycospheric bacteria in cyanobacterial proliferation was determined through coculturing of heterotrophic bacteria with an axenic Microcystis aeruginosa strain and by metatranscriptomic analysis using field Microcystis aggregate samples. RESULTS: Abundant bacteria that carry C-P lyase clusters were identified in plankton samples from freshwater Lakes Dianchi and Taihu during Microcystis bloom periods. Metagenomic analysis of 162 non-axenic laboratory strains of cyanobacteria (consortia cultures containing heterotrophic bacteria) showed that 20% (128/647) of high-quality bins from eighty of these consortia encode intact C-P lyase clusters, with an abundance ranging up to nearly 13%. Phycospheric bacterial phosphonate catabolism genes were expressed continually across bloom seasons, as demonstrated through metatranscriptomic analysis using sixteen field Microcystis aggregate samples. Coculturing experiments revealed that although Microcystis cultures did not catabolize methylphosphonate when axenic, they demonstrated sustained growth when cocultured with phosphonate-utilizing phycospheric bacteria in medium containing methylphosphonate as the sole source of phosphorus. CONCLUSIONS: The recruitment of heterotrophic phosphonate-degrading phycospheric bacteria by cyanobacteria is a hedge against phosphorus scarcity by facilitating phosphonate availability. Cyanobacterial consortia are likely primary contributors to aquatic phosphonate mineralization, thereby facilitating sustained cyanobacterial growth, and even bloom maintenance, in phosphate-deficient waters. Video Abstract.

[Effect of Rhizophagus intraradices on growth of Salvia miltiorrhiza].

The study aimed to explore the effects of inoculation of Rhizophagus intraradices on the biomass, effective component content, and endogenous hormone content of Salvia miltiorrhiza through pot experiments. The number of leaves, plant height, dry weight of aboveground and underground parts, branch number, root number, root length, root diameter, and other biomass were mea-sured by weighing and counting methods. The content of salvianolic acid B, caffeic acid, rosmarinic acid, tanshinone Ⅰ, tanshinone Ⅱ_A, cryptotanshinone, and other effective components was determined by ultra-high performance liquid chromatography. The content of ABA and GA_3 was determined by triple quadrupole mass spectrometry. The correlations between biomass and effective components and between effective components and plant hormones ABA and GA_3 were analyzed. The results showed that R. intraradices significan-tly increased the aboveground dry weight, leaf number, and root number of S. miltiorrhiza by 0.24-0.65 times, respectively. The content of salvianolic acid B and rosmarinic acid in the aboveground part and the content of salvianolic acid B, caffeic acid, rosmarinic acid, tanshinone Ⅰ, and tanshinone Ⅱ_A in the underground part were significantly increased by 0.44-1.78 times, respectively. R. intraradices infection significantly increased the GA_3/ABA values of aboveground and underground parts by 3.82 and 76.47 times, respectively. The correlation analysis showed that caffeic acid, the effective component of the aboveground part, was significantly positively correlated with plant height, tanshinone Ⅱ_A, the effective component of the underground part, was significantly positively correlated with biomass root number, cryptotanshinone, and dry weight, while rosmarinic acid was significantly negatively correlated with dry weight. There were significant positive correlations between cryptotanshinone and ABA, tanshinone Ⅱ_A and ABA and GA_3, and caffeic acid and GA_3. In conclusion, R. intraradices can promote the accumulation of biomass and secondary metabolites of S. miltiorrhiza and regulate the balance between plant hormones ABA and GA_3, thereby promoting the growth of S. miltiorrhiza.

The widespread capability of methylphosphonate utilization in filamentous cyanobacteria and its ecological significance.

Aquatic ecosystems comprise almost half of total global methane emissions. Recent evidence indicates that a few strains of cyanobacteria, the predominant primary producers in bodies of water, can produce methane under oxic conditions with methylphosphonate serving as substrate. In this work, we have screened the published 2 568 cyanobacterial genomes for genetic elements encoding phosphonate-metabolizing enzymes. We show that phosphonate degradation (phn) gene clusters are widely distributed in filamentous cyanobacteria, including several bloom-forming genera. Algal growth experiments revealed that methylphosphonate is an alternative phosphorous source for four of five tested strains carrying phn clusters, and can sustain cellular metabolic homeostasis of strains under phosphorus stress. Liberation of methane by cyanobacteria in the presence of methylphosphonate occurred mostly during the light period of a 12 h/12 h diurnal cycle and was suppressed in the presence of orthophosphate, features that are consistent with observations in natural aquatic systems under oxic conditions. The results presented here demonstrate a genetic basis for ubiquitous methane emission via cyanobacterial methylphosphonate mineralization, while contributing to the phosphorus redox cycle.

[Influence of aqueous extract of Aralia echinocaulis Hand.-Mazz on the expression of fracture healing-related factor receptors].

OBJECTIVE: To investigate the influence of aqueous extract of Aralia echinocaulis Hand.-Mazz on the expression of fracture healing-ralated factor receptors. METHODS: Single factor model was set up in SD rat. Selecting 14 and 28 days in the experiment. Immunohistochemistry was employed to determine the expression of Fibroblast growth factor receptor 2 (FGFR2), Fms-like tyrosine kinase (Flt-1) and Fetal licer kinase (Flk-1) at 14 and 28 days after model establishing. RESULTS: The expression of Flt-1 and Flk-1 at 14 days (the latter was more remarkable) were obviously promoted in High dose group of aqueous extract of Aralia echinocaulis Hand.-Mazz, and higher than that in normal group and model group. The expression of FGFR2 in the high dose group of Aralia echinocaulis Hand -Mazz was also promoted visibility, close to that in the compare group (traditional Chinese medicine), but higher than than in the model group. There was no significant difference among them. At 28 days, the expression of FGFR2, Flt-1 and Flk-1 in all groups decreased except normal group, and got higher expression in model groups than each control groups. CONCLUSION: Aqueous extract of Aralia echinocaulis Hand.-Mazz can promote angiogenesis in fracture healing, improve the activity and aggregation of fibroblasts, osteoblasts and chondrocytes. It also helps to quicken ossification in the cartilage and promote fracture healing.