Two-Component-System RspA1/A2-Dependent Regulation on Primary Metabolism in Streptomyces albus A30 Cultivated With Glutamate as the Sole Nitrogen Source

Trends in the two-component system's role in the synthesis of antibiotics by Streptomyces

Despite the advances in understanding the regulatory networks for secondary metabolite production in Streptomyces, the participation of the two-component systems (TCS) in this process still requires better characterization. These sensing systems and their responses to environmental stimuli have been described by evaluating mutant strains with techniques that allow in-depth regulatory responses. However, defining the stimulus that triggers their activation is still a task. The transmembrane nature of the sensor kinases and the high content of GC in the streptomycetes represent significant challenges in their study. In some examples, adding elements to the assay medium has determined the respective ligand. However, a complete TCS description and characterization requires specific amounts of the involved proteins that are most difficult to obtain. The availability of enough sensor histidine kinase concentrations could facilitate the identification of the ligand-protein interaction, and besides would allow the establishment of its phosphorylation mechanisms and determine their tridimensional structure. Similarly, the advances in the development of bioinformatics tools and novel experimental techniques also promise to accelerate the TCSs description and provide knowledge on their participation in the regulation processes of secondary metabolite formation. This review aims to summarize the recent advances in the study of TCSs involved in antibiotic biosynthesis and to discuss alternatives to continue their characterization. KEY POINTS: • TCSs are the environmental signal transducers more abundant in nature. • The Streptomyces have some of the highest number of TCSs found in bacteria. • The study of signal transduction between SHKs and RRs domains is a big challenge.

Production of polyhydroxyalkanoates from propylene oxide saponification wastewater residual sludge using volatile fatty acids and bacterial community succession

The active sludge treating propylene oxide saponification wastewater has heavy salt concentration and is hard to treat. The integration of the residual sludge treatment with polyhydroxyalkanoates (PHA) production may provide an economic and environment friendly solution. PHA production was therefore studied in two sequencing biological reactors with effective volume of 30 L using the active sludge. The two reactors, named as SBR-I and SBR-II, were fed with acetic acid, and a mixture of acetic acid and propionic acid respectively. PHA was obtained with a yield of 9.257 g/L in SBR-II. Also, the proportion of 3-hydroxyvalarate was enhanced from 5% to 30% in comparison to SBR-I (5.471 g/L). Illumina MiSeq and Pacific Biosciences sequencing platforms were used to evaluate the community structure, which revealed that the bacterial genera showed a high degree of diversity in the PHA accumulating microbial community. Azoarcus was the most dominant PHA accumulating microorganism after acclimation.