Tannic Acid Modulation of Substrate Utilization, Microbial Community, and Metabolic Traits in Sludge Anaerobic Fermentation for Volatile Fatty Acid Promotion.

Anaerobic fermentation is a crucial route to realize effective waste activated sludge (WAS) resource recovery and utilization, while the overall efficiency is commonly restrained by undesirable disruptors (i.e., chemical dewatering agents). This work unveiled the unexpectedly positive effects of biodewatering tannic acid (TA) on the volatile fatty acids (VFAs) biosynthesis during WAS anaerobic fermentation. The total VFAs yield was remarkably increased by 15.6 folds with enriched acetate and butyrate in TA-occurred systems. TA was capable to disintegrate extracellular polymeric substances to promote the overall organics release. However, TA further modulated the soluble proteins structure by hydrogen bonding and hydrophobic interactions, resulting in the decrease of proteins bioavailability and consequential alteration of metabolic substrate feature. These changes reshaped the microbial community and stimulated adaptive regulatory systems in hydrolytic-acidogenic bacteria. The keystone species for carbohydrate metabolism (i.e., Solobacterium and Erysipelotrichaceae) were preferentially enriched. Also, the typical quorum sensing (i.e., enhancing substrate transport) and two-component systems (i.e., sustaining high metabolic activity) were activated to promote the microbial networks connectivity and ecological cooperative behaviors in response to TA stress. Additionally, the metabolic functions responsible for carbohydrate hydrolysis, transmembrane transport, and intracellular metabolism as well as VFA biosynthesis showed increased relative abundance, which maintained high microbial activities for VFAs biosynthesis. This study underscored the advantages of biodewatering TA for WAS treatment in the context of resource recovery and deciphered the interactive mechanisms.

The Immediate Hotspot of Microbial Nitrogen Cycling in an Oil-Seed Rape (Brassica campestris L.) Soil System Is the Bulk Soil Rather Than the Rhizosphere after Biofertilization.

Biofertilizers are substances that promote plant growth through the efficacy of living microorganisms. The functional microbes comprising biofertilizers are effective mediators in plant-soil systems in the regulation of nitrogen cycling, especially in nitrification repression. However, the deterministic or stochastic distribution of the functional hotspot where microbes are active immediately after biofertilization is rarely investigated. Here, pot experiments with oil-seed rape (Brassica campestris L.) were conducted with various chemical and biological fertilizers in order to reveal the distribution of the hotspot after each fertilization. A stimulated dynamic of the nitrogen cycling-related genes in the bulk soil inferred that the bulk soil was likely to be the hotspot where the inoculated bacterial fertilizers dominated the nitrogen cycle. Furthermore, a network analysis showed that bulk soil microbial communities were more cooperative than those in the rhizosphere after biofertilization, suggesting that the microbiome of the bulk soils were more efficient for nutrient cycling. In addition, the relatively abundant ammonia-oxidizing bacteria and archaea present in the networks of bulk soil microbial communities further indicated that the bulk soil was the plausible hotspot after the application of the biofertilizers. Therefore, our research provides a new insight into the explicit practice of plant fertilization and agricultural management, which may improve the implementational efficiency of biofertilization.

Pleiotropic mutations can rapidly evolve to directly benefit self and cooperative partner despite unfavorable conditions.

Cooperation, paying a cost to benefit others, is widespread. Cooperation can be promoted by pleiotropic 'win-win' mutations which directly benefit self (self-serving) and partner (partner-serving). Previously, we showed that partner-serving should be defined as increased benefit supply rate per intake benefit. Here, we report that win-win mutations can rapidly evolve even under conditions unfavorable for cooperation. Specifically, in a well-mixed environment we evolved engineered yeast cooperative communities where two strains exchanged costly metabolites, lysine and hypoxanthine. Among cells that consumed lysine and released hypoxanthine, ecm21 mutations repeatedly arose. ecm21 is self-serving, improving self's growth rate in limiting lysine. ecm21 is also partner-serving, increasing hypoxanthine release rate per lysine consumption and the steady state growth rate of partner and of community. ecm21 also arose in monocultures evolving in lysine-limited chemostats. Thus, even without any history of cooperation or pressure to maintain cooperation, pleiotropic win-win mutations may readily evolve to promote cooperation.