Comparative metagenomic analysis provides novel insights into the ecophysiology of Myxococcota in activated sludge systems

Myxobacteria, belonging to the phylum Myxococcota, are ubiquitous in soil, marine, and other environments. Recent metagenomic sequencing analysis has shown that Myxococcota are predominant in activated sludge systems; however, their ecophysiological traits remain unclear. In this study, we evaluated the potential biological functions of 46 metagenomic bins of Myxococcota reconstructed from activated sludge samples from four municipal sewage treatment plants. The results showed that most Myxococcota bins had an almost complete set of genes associated with glycolysis and the TCA cycle. Palsa-1104 and Polyangiales bins contain glycoside hydrolase GH13 and peptidase M23, which are presumably involved in the lysis of the cell wall and cellular cytoplasm, indicating that part of the Myxococcota from activated sludge can prey on other microorganisms. The previously known cell contact-dependent predatory functions of Myxococcus xanthus are conserved in the family Myxococcaceae, though not in other families. Two bins belonging to Palsa-1104 had phototrophic gene clusters, suggesting that these bins may have both heterotrophic and autotrophic metabolisms. Assessment of the social behavior of the activated sludge Myxococcota, a FruA gene, and a C-signal gene involved in the regulation of fruiting body formation were lacking in Myxococcota bins, suggesting that they are incapable of fruiting body formation. In addition, multiple bins of Myxococcota had novel secondary metabolite biosynthesis gene clusters that may be used for the predation of other bacteria in the activated sludge. Our metagenome-based analyses provide novel insights into the microbial interactions associated with Myxococcota in activated sludge ecosystems.