The disruption of bacterial signaling (quorum quenching) has been proven to be an innovative approach to influence the behavior of bacteria. In particular, lactonase enzymes that are capable of hydrolyzing the N- acyl homoserine lactone (AHL) molecules used by numerous bacteria, were reported to inhibit biofilm formation, including those of freshwater microbial communities. However, insights and tools are currently lacking to characterize, understand and explain the effects of signal disruption on complex microbial communities. Here, we produced silica capsules containing an engineered lactonase that exhibits quorum quenching activity. Capsules were used to design a filtration cartridge to selectively degrade AHLs from a recirculating bioreactor. The growth of a complex microbial community in the bioreactor, in the presence or absence of lactonase, was monitored over a 3-week period. Dynamic population analysis revealed that signal disruption using a quorum quenching lactonase can effectively reduce biofilm formation in the recirculating bioreactor system and that biofilm inhibition is concomitant to drastic changes in the composition, diversity and abundance of soil bacterial communities within these biofilms. Effects of the quorum quenching lactonase on the suspension community also affected the microbial composition, suggesting that effects of signal disruption are not limited to biofilm populations. This unexpected finding is evidence for the importance of signaling in the competition between bacteria within communities. This study provides foundational tools and data for the investigation of the importance of AHL-based signaling in the context of complex microbial communities.

Synechococcus elongatus PCC 7942 is a model cyanobacterium for study of the circadian clock, photosynthesis, and bioproduction of chemicals, yet nearly 40% of its gene identities and functions remain unknown, in part due to limitations of the existing genetic toolkit. While classical techniques for the study of genes (e.g., deletion or mutagenesis) can yield valuable information about the absence of a gene and its associated protein, there are limits to these approaches, particularly in the study of essential genes. Herein, we developed a tool for inducible degradation of target proteins in S. elongatus by adapting a method using degron tags from the Mesoplasma florum transfer-mRNA (tmRNA) system. We observed that M. florum lon protease can rapidly degrade exogenous and native proteins tagged with the cognate sequence within hours of induction. We used this system to inducibly degrade the essential cell division factor, FtsZ, as well as shell protein components of the carboxysome. Our results have implications for carboxysome biogenesis and the rate of carboxysome turnover during cell growth. Lon protease control of proteins offers an alternative approach for the study of essential proteins and protein dynamics in cyanobacteria.

An adsorbent silica biogel material was developed via silica gel encapsulation of Pseudomonas sp. NCIB 9816-4, a bacterium that degrades a broad spectrum of aromatic pollutants. The adsorbent matrix was synthesized using silica precursors methyltrimethoxysilane and tetramethoxysilane to maximize the adsorption capacity of the matrix while maintaining a highly networked and porous microstructure. The encapsulated bacteria enhanced the removal rate and capacity of the matrix for an aromatic chemical mixture. Repeated use of the material over four cycles was conducted to demonstrate that the removal capacity could be maintained with combined adsorption and biodegradation. The silica biogel can thus be used extensively without the need for disposal, as a result of continuous biodegradation by the encapsulated bacteria. However, an inverse trend was observed with the ratio of biodegradation to adsorption as a function of log K, suggesting increasing mass-transport limitation for the most hydrophobic chemicals used (log K > 4).

aIn addition to methane gas, higher-value resources such as hydrogen gas are produced during anaerobic wastewater treatment. They are, however, immediately consumed by other organisms. To recover these high-value resources, not only do the desired phenotypes need to be retained in the anaerobic reactor, but the undesired ones need to be washed out. In this study, a well-established alginate-based polymer gel, with and without a coating layer, was used to selectively encapsulate hydrogen-producing biomass in beads to achieve high-rate recovery of hydrogen during anaerobic wastewater treatment. , as well as a composite coating on the beads, consisting of alternating layers of polyethylenimine and silica hydrogel, were investigated with respect to their performance, specifically, their mass transfer characteristics and their differential ability to retain the encapsulated biomass. Although the coating reduced the escape rate of encapsulated biomass from the beads, all alginate polymer matrices without coating effectively retained biomass. Fast diffusion of dissolved organic carbon (DOC) through the polymer gel was observed in both Ca-alginate and Sr-alginate without coating. The coating, however, decreased either the diffusivity or the permeability of the DOC depending on whether the DOC was from synthetic wastewater (more lipids and proteins) or real brewery wastewater (more sugars). Consequently, the encapsulation system with coating became diffusion limited when brewery wastewater with high chemical oxygen demand was fed, resulting in a lower hydrogen production rate than the uncoated encapsulation systems. In all cases the encapsulated biomass was able to produce hydrogen, even at a hydraulic residence time of 45 min. Although there are limitations to this system, the used of encapsulated biomass for resource recovery from wastewater shows promise, particularly for highrate systems in which the retention of specific phenotypes is desired.