Strain NJES-13^T is the type strain and currently the only species of the newly established actinobacteria genera Aptenodytes in the family Dermatophilaceae isolated from the gut microbiota of the Antarctic emperor penguin. This strain demonstrated excellent bioflocculation activity with bacteria-derived exopolysaccharides (EPSs). Moreover, it produced bioactive angucycline/angucyclinone derivatives (ADs) and contained one type III polyketide synthase (T3PKS), thus demonstrating great potential to produce novel bioactive compounds. However, the low productivity of the potential new AD metabolite was the main obstacle for its chemical structure elucidation. In this study, to increase the concentration of targeted metabolites, the influence of cellular morphology on AD metabolism in strain NJES-13^T was determined using glass bead-enhanced fermentation. Based on the cellular ultra-structural observation driven by bacterial EPSs, and quantitative analysis of the targeted metabolites, the successful increasing of the productivity of three AD metabolites was achieved. Afterward, a new frigocyclinone analogue was isolated and then identified as 2-hydroxy-frigocyclinone, as well as two other known ADs named 2-hydroxy-tetrangomycin (2-HT) and gephyromycin (GPM). Three AD metabolites were found to demonstrate different bioactivities. Both C-2 hydroxyl substitutes, 2-hydroxy-tetrangomycin and 2-hydroxy-frigocyclinone, exhibited variable inhibitory activities against Staphylococcus aureus, Bacillus subtilis and Candida albicans. Moreover, the newly identified 2-hydroxy-frigocyclinone also showed significant cytotoxicity against three tested human-derived cancerous cell lines (HL-60, Bel-7402 and A549), with all obtained IC₅₀ values less than 10 µM. Based on the genetic analysis after genomic mining, the plausible biogenetic pathway of the three bioactive ADs in strain NJES-13^T was also proposed.

Whether exogenous vitamin K1 (VK1) promotes microalgal growth is unknown. This study reports for the first time that Bacillus megaterium can promote the growth of Chlorella pyrenoidosa, an effect possibly mediated by VK1. To confirm this finding and clarify the corresponding mechanism, the effects of exogenous VK1 on the growth and lipid production of C. pyrenoidosa were studied. The results showed that the microalgal cell density, chlorophyll a content, lipid content, and lipid productivity increased by 117%, 90%, 291%, and 247%, respectively, following the addition of 0.3 g/L exogenous VK1. Additionally, the microalgal Fv/Fo, Fv/Fm, and Fm/Fo were also improved by the VK1, indicating that VK1 promoted microalgae growth by increasing microalgal photosynthesis activities. The microalgal genes of lipid synthesis, including the acetyl-CoA carboxylase gene, malonyl-transferase gene, 3-oxoacylsynthase I gene, and 3-oxoacyl-[acyl-carrier-protein] synthase II gene, were all up-regulated by VK1 at the transcript level, revealing the promotion mechanism of VK1 on microalgal lipid production. Moreover, the total phosphorus utilization of the C. pyrenoidosa reached nearly 100%, indicating its excellent phosphorus utilization ability. The results are beneficial for exploring a more effective technology of utilizing C. pyrenoidosa for biofuel production and provide a new perspective on understanding the interaction mechanism between bacteria and microalgae.