[Influencing factors of phosphate solubilizing capacity of Aspergillus niger and optimization of its culture condition].

In this study, we investigated factors affecting the phosphate solubilizing capacity of Aspergillus niger. A strain named A. niger Xj-2 was isolated by single-spore isolation, with phosphate solubilizing capacity of 539.90 mg·L-1 in liquid medium. The simulated process of fermentation kinetics showed that phosphate concentration reached equilibrium after 4 d cultivation, indicating that the optimal fermentation time was around 4 d. Phosphate solubilization capacity of strain Xj-2 in different phosphorus-source culture media followed the order: calcium phosphate (539.90 mg·L-1)>zinc phosphate (238.45 mg·L-1)>ferric phosphate (182.64 mg·L-1)>phosphate rock power (71.80 mg·L-1) > aluminum phosphate (24.40 mg·L-1). We further examined the optimal condition of strain Xj-2 for phosphate solubilization by response surface optimization combined with single factor experiments. Results showed that the influence of various factors on the phosphate solubilizing capacity of strain Xj-2 was in the order: carbon source > microbial density > pH. The maximum phosphate solubilizing capacity (616.81 mg·L-1) could be achieved under the following condition with 10.00 g·L-1 glucose, 0.79 g·L-1 urea, 35 ℃, the initial pH of medium 6.0, 3.8% microbial density and 160 r·min-1 rotating speed.

PIM-1 modulates cellular senescence and links IL-6 signaling to heterochromatin formation.

Cellular senescence is a stable state of proliferative arrest that provides a barrier against malignant transformation and contributes to the antitumor activity of certain chemotherapies. Unexpectedly, we found that the expression of proto-oncogene PIM-1, which can promote tumorigenesis, is induced at transcriptional level during senescence. Inhibition of PIM-1 alleviated both replicative and oncogene-induced senescence. Conversely, ectopic expression of PIM-1 resulted in premature senescence. We also revealed that PIM-1 interacts with and phosphorylates heterochromatin protein 1γ (HP1γ) on Ser93. This PIM-1-mediated HP1γ phosphorylation enhanced HP1γ's capacity to bind to H3K9me3, resulting in heterochromatin formation and suppression of proliferative genes, such as CCNA2 and PCNA. Analysis of the mechanism underlying the up-regulation of PIM-1 expression during senescence demonstrated that IL-6, a critical regulator of cellular senescence, is responsible for PIM-1 induction. Our study demonstrated that PIM-1 is a key component of the senescence machinery that contributes to heterochromatin formation. More importantly, we demonstrated that PIM-1 is also a direct target of IL-6/STAT3 signaling and mediates cytokine-induced cellular senescence.