Archaea join the conversation: detection of AHL-like activity across a range of archaeal isolates

Methanogenic partner influences cell aggregation and signalling of Syntrophobacterium fumaroxidans

For several decades, the formation of microbial self-aggregates, known as granules, has been extensively documented in the context of anaerobic digestion. However, current understanding of the underlying microbial-associated mechanisms responsible for this phenomenon remains limited. This study examined morphological and biochemical changes associated with cell aggregation in model co-cultures of the syntrophic propionate oxidizing bacterium Syntrophobacterium fumaroxidans and hydrogenotrophic methanogens, Methanospirillum hungatei or Methanobacterium formicicum. Formerly, we observed that when syntrophs grow for long periods with methanogens, cultures tend to form aggregates visible to the eye. In this study, we maintained syntrophic co-cultures of S. fumaroxidans with either M. hungatei or M. formicicum for a year in a fed-batch growth mode to stimulate aggregation. Millimeter-scale aggregates were observed in both co-cultures within the first 5 months of cultivation. In addition, we detected quorum sensing molecules, specifically N-acyl homoserine lactones, in co-culture supernatants preceding the formation of macro-aggregates (with diameter of more than 20 μm). Comparative transcriptomics revealed higher expression of genes related to signal transduction, polysaccharide secretion and metal transporters in the late-aggregation state co-cultures, compared to the initial ones. This is the first study to report in detail both biochemical and physiological changes associated with the aggregate formation in syntrophic methanogenic co-cultures. KEYPOINTS: • Syntrophic co-cultures formed mm-scale aggregates within 5 months of fed-batch cultivation. • N-acyl homoserine lactones were detected during the formation of aggregates. • Aggregated co-cultures exhibited upregulated expression of adhesins- and polysaccharide-associated genes.

Archaeal Tubulin-like Proteins Modify Cell Shape in Haloferax volcanii during Early Biofilm Development

Tubulin, an extensively studied self-assembling protein, forms filaments in eukaryotic cells that affect cell shape, among other functions. The model archaeon Haloferax volcanii uses two tubulin-like proteins (FtsZ1/FtsZ2) for cell division, similar to bacteria, but has an additional six related tubulins called CetZ. One of them, CetZ1, was shown to play a role in cell shape. Typically, discoid and rod shapes are observed in planktonic growth, but under biofilm formation conditions (i.e., attached to a substratum), H. volcanii can grow filamentously. Here, we show that the deletion mutants of all eight tubulin-like genes significantly impacted morphology when cells were allowed to form a biofilm. ΔftsZ1, ΔcetZ2, and ΔcetZ4-6 created longer, less round cells than the parental and a higher percentage of filaments. ΔcetZ1 and ΔcetZ3 were significantly rounder than the parental, and ΔftsZ2 generated larger, flat, amorphic cells. The results show all tubulin homologs affect morphology at most timepoints, which therefore suggests these genes indeed have a function.

Enhancement of biomethane recovery from batch anaerobic digestion by exogenously adding an N-acyl homoserine lactone cocktail

Biomethane recovered through anaerobic digestion (AD) is a renewable, sustainable, and cost-effective alternative energy source that has the potential to help address rising energy demands. Efficient bioconversion during AD depends on the symbiotic relationship between hydrolytic bacteria and methanogenic archaea. Interactions between microorganisms occur in every biological system via a phenomenon known as quorum sensing (QS), in which signaling molecules are simultaneously transmitted and detected as a mode of cell-to-cell communication. However, there's still a lack of understanding on how QS works in the AD system, where diverse bacteria and archaea interact in a complex manner. In this study, different concentrations (0.5 and 5 μM) of signaling molecules in the form of an N-acyl homoserine lactone cocktail (C6-, C8-, C10-, and 3-oxo-C6-HSL) were prepared and introduced into anaerobic batch reactors to clearly assess how QS affects AD systems. It was observed that the methane yield increased with the addition of AHLs: a 5 μM AHL cocktail improved the methane yield (341.9 mL/g-COD) compared to the control without AHLs addition (285.9 mL/g-COD). Meanwhile, evidence of improved microbial growth and cell aggregation was noticed in AHLs-supplemented systems. Our findings also show that exogenously adding AHLs alters the microbial community structure by increasing the overall bacterial and archaeal population counts while favoring the growth of the methanogenic archaea group, which is essential in biomethane synthesis.

Towards understanding mechanisms and functional consequences of bacterial interactions with members of various kingdoms in complex biofilms that abound in nature

The microbial world represents a phenomenal diversity of microorganisms from different kingdoms of life which occupy an impressive set of ecological niches. Most, if not all, microorganisms once colonise a surface develop architecturally complex surface-adhered communities which we refer to as biofilms. They are embedded in polymeric structural scaffolds serve as a dynamic milieu for intercellular communication through physical and chemical signalling. Deciphering microbial ecology of biofilms in various natural or engineered settings has revealed co-existence of microorganisms from all domains of life, including Bacteria, Archaea and Eukarya. The coexistence of these dynamic microbes is not arbitrary, as a highly coordinated architectural setup and physiological complexity show ecological interdependence and myriads of underlying interactions. In this review, we describe how species from different kingdoms interact in biofilms and discuss the functional consequences of such interactions. We highlight metabolic advances of collaboration among species from different kingdoms, and advocate that these interactions are of great importance and need to be addressed in future research. Since trans-kingdom biofilms impact diverse contexts, ranging from complicated infections to efficient growth of plants, future knowledge within this field will be beneficial for medical microbiology, biotechnology, and our general understanding of microbial life in nature.

Archaea, tiny helpers of land plants

Archaea are members of most microbiomes. While archaea are highly abundant in extreme environments, they are less abundant and diverse in association with eukaryotic hosts. Nevertheless, archaea are a substantial constituent of plant-associated ecosystems in the aboveground and belowground phytobiome. Only a few studies have investigated the role of archaea in plant health and its potential symbiosis in ecosystems. This review discusses recent progress in identifying how archaea contribute to plant traits such as growth, adaptation to abiotic stresses, and immune activation. We synthesized the most recent functional and molecular data on archaea, including root colonization and the volatile emission to activate plant systemic immunity. These data represent a paradigm shift in our understanding of plant-microbiota interactions.