Granular biofilms: Function, application, and new trends as model microbial communities

Trego, Anna Christine; Mills, Simon; Collins, Gavin

doi:10.1080/10643389.2020.1769433

Cited by 30 publications

(31 citation statements)

References 142 publications

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“…To this end, granular biofilms, usually found in engineered wastewater treatment plants ( Fig. 1 ), are emerging as ideal “playgrounds” to test fundamental concepts in microbial ecology ( 5 , 8 , 9 ). Granules are self-immobilized, usually spherical, biofilm aggregates, which, in all identified cases, contain highly complex and diverse microbial communities comprised of multiple trophic groups working in coordination or competing with one another ( 10 – 13 ).…”

Section: Introductionmentioning

confidence: 99%

Size Shapes the Active Microbiome of Methanogenic Granules, Corroborating a Biofilm Life Cycle

et al. 2020

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Methanogenic archaea are key players in cycling organic matter in nature but also in engineered waste treatment systems, where they generate methane, which can be used as a renewable energy source. In such systems in the built environment, complex methanogenic consortia are known to aggregate into highly organized, spherical granular biofilms comprising the interdependent microbial trophic groups mediating the successive stages of the anaerobic digestion (AD) process. This study separated methanogenic granules into a range of discrete size fractions, hypothesizing different biofilm growth stages, and separately supplied each with specific substrates to stimulate the activity of key AD trophic groups, including syntrophic acid oxidizers and methanogens. Rates of specific methanogenic activity were measured, and amplicon sequencing of 16S rRNA gene transcripts was used to resolve phylotranscriptomes across the series of size fractions. Increased rates of methane production were observed in each of the size fractions when hydrogen was supplied as the substrate compared with those of volatile fatty acids (acetate, propionate, and butyrate). This was connected to a shift toward hydrogenotrophic methanogenesis dominated by Methanobacterium and Methanolinea. Interestingly, the specific active microbiomes measured in this way indicated that size was significantly more important than substrate in driving the structure of the active community in granules. Multivariate integration studywise discriminant analysis identified 56 genera shaping changes in the active community across both substrate and size. Half of those were found to be upregulated in the medium-sized granules, which were also the most active and potentially of the most important size, or life stage, for precision management of AD systems. IMPORTANCE Biological wastewater conversion processes collectively constitute one of the single biggest worldwide applications of microbial communities. There is an obvious requirement, therefore, to study the microbial systems central to the success of such technologies. Methanogenic granules, in particular, are architecturally fascinating biofilms that facilitate highly organized cooperation within the metabolic network of the anaerobic digestion (AD) process and, thus, are especially intriguing model systems for microbial ecology. This study, in a way not previously reported, provoked syntrophic and methanogenic activity and the structure of the microbial community, using specific substrates targeting the key trophic groups in AD. Unexpectedly, granule size more strongly than substrate shaped the active portion of the microbial community. Importantly, the findings suggest the size, or age, of granules inherently shapes the active microbiome linked to a life cycle. This provides exciting insights into the function of, and the potential for additional modeling of biofilm development in, methanogenic granules.

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Section: Introductionmentioning

confidence: 99%

Size Shapes the Active Microbiome of Methanogenic Granules, Corroborating a Biofilm Life Cycle

et al. 2020

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“…However, as a whole, the understanding of how communities assemble in ecosystems of the built environment remains under-studied. Yet, they are wide-spread applications of biotechnology, as well as a source of highly replicated microbial communities (Leventhal et al, 2018;Trego et al, 2020). Anaerobic granules, for example, form through selfimmobilisation of bacteria and archaea (Liu and Tay, 2004) and are crucial to the success of high-rate, upflow anaerobic systems such as the upflow anaerobic sludge bed (UASB) bioreactor (Lettinga, 1995).…”

Section: Introductionmentioning

confidence: 99%

Combined Stochastic and Deterministic Processes Drive Community Assembly of Anaerobic Microbiomes During Granule Flotation

et al. 2021

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Advances in null-model approaches have resulted in a deeper understanding of community assembly mechanisms for a variety of complex microbiomes. One under-explored application is assembly of communities from the built-environment, especially during process disturbances. Anaerobic digestion for biological wastewater treatment is often underpinned by retaining millions of active granular biofilm aggregates. Flotation of granules is a major problem, resulting in process failure. Anaerobic aggregates were sampled from three identical bioreactors treating dairy wastewater. Microbiome structure was analysed using qPCR and 16S rRNA gene amplicon sequencing from DNA and cDNA. A comprehensive null-model approach quantified assembly mechanisms of floating and settled communities. Significant differences in diversity were observed between floating and settled granules, in particular, we highlight the changing abundances of Methanosaeta and Lactococcus. Both stochastic and deterministic processes were important for community assembly. Homogeneous selection was the primary mechanism for all categories, but dispersal processes also contributed. The lottery model was used to identify clade-level competition driving community assembly. Lottery “winners” were identified with different winners between floating and settled groups. Some groups changed their winner status when flotation occurred. Spirochaetaceae, for example, was only a winner in settled biomass (cDNA-level) and lost its winner status during flotation. Alternatively, Arcobacter butzerli gained winner status during flotation. This analysis provides a deeper understanding of changes that occur during process instabilities and identified groups which may be washed out—an important consideration for process control.

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“…The movement and shape mitigate boundary layer resistances and enhance the mass transfer of substrates across the biofilm granule (Baeten et al 2019). For these reasons, granular biofilms have been successfully developed in different bioreactor configurations, for various processes, such as aerobic, anaerobic and partial nitritation-anammox treatments (Trego et al 2020b).…”

Section: Introductionmentioning

confidence: 99%

“…Many studies have explored the granulation process and numerous theories have been proposed. Hydrodynamic conditions generated by liquid up-flow velocity, gas production, particle-particle collision, mixing systems and bioreactor geometry are universally recognized as key factors in the granulation process as well as throughout the entire life cycle of the granules (Liu and Tay 2002;Trego et al 2020b;Lettinga et al 1980). Indeed, suitable hydrodynamic conditions are required to initiate the granulation process by promoting, and improving, the aggregation of planktonic biomass (Lemaire et al 2008).…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, intense hydrodynamic conditions induce high shear forces on the granule surface, influencing size, shape, structure and density of the granules (Liu and Tay 2002;Di Iaconi et al 2006), and regulate a continuous process of aggregation and breaking that leads to the formation of an increasing number of granules. High shear forces are thought to stimulate the production of EPS, which represents a further beneficial factor for granulation as it increases cell surface hydrophobicity (Trego et al 2020b). Several studies also consider the granulation process to be the result of an organized process driven by pioneering microbial species with specific, key characteristics (Pol et al 2004;Wiegant 1988).…”

Section: Introductionmentioning

confidence: 99%

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Multiscale Modelling of De Novo Anaerobic Granulation

et al. 2021

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A multiscale mathematical model is presented to describe de novo granulation, and the evolution of multispecies granular biofilms, in a continuously fed bioreactor. The granule is modelled as a spherical free boundary domain with radial symmetry. The equation governing the free boundary is derived from global mass balance considerations and takes into account the growth of sessile biomass as well as exchange fluxes with the bulk liquid. Starting from a vanishing initial value, the expansion of the free boundary is initiated by the attachment process, which depends on the microbial species concentrations within the bulk liquid and their specific attachment velocity. Nonlinear hyperbolic PDEs model the growth of the sessile microbial species, while quasi-linear parabolic PDEs govern the dynamics of substrates and invading species within the granular biofilm. Nonlinear ODEs govern the evolution of soluble substrates and planktonic biomass within the bulk liquid. The model is applied to an anaerobic, granular-based bioreactor system, and solved numerically to test its qualitative behaviour and explore the main aspects of de novo anaerobic granulation: ecology, biomass distribution, relative abundance, dimensional evolution of the granules and soluble substrates, and planktonic biomass dynamics within the bioreactor. The numerical results confirm that the model accurately describes the ecology and the concentrically layered structure of anaerobic granules observed experimentally, and that it can predict the effects on the process of significant factors, such as influent wastewater composition; granulation properties of planktonic biomass; biomass density; detachment intensity; and number of granules.

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Granular biofilms: Function, application, and new trends as model microbial communities

Cited by 30 publications

References 142 publications

Size Shapes the Active Microbiome of Methanogenic Granules, Corroborating a Biofilm Life Cycle

Size Shapes the Active Microbiome of Methanogenic Granules, Corroborating a Biofilm Life Cycle

Combined Stochastic and Deterministic Processes Drive Community Assembly of Anaerobic Microbiomes During Granule Flotation

Multiscale Modelling of De Novo Anaerobic Granulation

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