Transition of a solitary to a biofilm community life style in bacteria: a survival strategy with division of labour (original) (raw)
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Biofilm: multicellular living of the unicellular bacteria
Unicellular bacterium in nature prefers to gather round to form a surface attached multi-cellular consortium called biofilm rather than living as an isolated planktonic cell. Biofilms comprise of the bacterial cells attached to a biotic or abiotic surface and the extracellular polymeric substances excreted by the participant cells. Many bacteria can respond to environmental signals to form biofilm and to detach from it. Cells within biofilms are distinct from the free swimming planktonic cells – both physiologically and genetically. Biofilms provide the bacteria with various survival and metabolic advantages over the planktonic form. Formation of biofilm is crucial for the survival of the bacteria in the environment and for their interaction within and out of the species. Mixed species biofilms better resemble the environmental biofilm consortia where a group of related bacteria gather onto a single surface and interact among them for the betterment of the whole community. This revi...
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Biofilms are organised heterogeneous assemblages of microbial cells that are encased within a self-produced matrix. Current estimates suggest that up to 80% of bacterial and archaeal cells reside in biofilms. Since biofilms are the main mode of microbial life, understanding their biology and functions is critical, especially as controlling biofilm growth is essential in industrial, infrastructure and medical contexts. Here we discuss biofilms both as collections of individual cells, and as multicellular biological individuals, and introduce the concept of biofilms as unique incubators of diversity for the microbial world.
From the Cover: Cooperation and conflict in microbial biofilms
Proceedings of The National Academy of Sciences, 2007
Biofilms, in which cells attach to surfaces and secrete slime (polymeric substances), are central to microbial life. Biofilms are often thought to require high levels of cooperation because extracellular polymeric substances are a shared resource produced by one cell that can be used by others. Here we examine this hypothesis by using a detailed individual-based simulation of a biofilm to investigate the outcome of evolutionary competitions between strains that differ in their level of polymer production. Our model includes a biochemical description of the carbon fluxes for growth and polymer production, and it explicitly calculates diffusion-reaction effects and the resulting solute gradients in the biofilm. An emergent property of these simple but realistic mechanistic assumptions is a strong evolutionary advantage to extracellular polymer production. Polymer secretion is altruistic to cells above a focal cell: it pushes later generations in their lineage up and out into better oxygen conditions, but it harms others; polymer production suffocates neighboring nonpolymer producers. This property, analogous to vertical growth in plants, suggests that polymer secretion provides a strong competitive advantage to cell lineages within mixed-genotype biofilms: global cooperation is not required. Our model fundamentally changes how biofilms are expected to respond to changing social conditions; the presence of multiple strains in a biofilm should promote rather than inhibit polymer secretion.
2005
When we think about bacteria, most of us imagine a watery milieu, with single-celled organisms swimming about. We might envision these solitary entities getting together with some of their brethren now and then to cause some disease or spoil some food, but once the job is done they return to their isolated existence. This image of bacterial existence, it turns out, is not only oversimplified but perhaps misleading as well. In nature, the majority of microorganisms live together in large numbers, attached to a surface. Rather than living as lonely hermits in tbe socalled planktonic form, most bacteria spend much of their lives in tbe microbial equivalent of a gated community— a biofilm.
Social evolution in bacterial biofilms
Most of the chronic infections are caused by collective lifestyle of bacteria called the biofilm. This is also a long-term survival strategy of bacteria in their natural environment, and the biofilms are notoriously known for their antimicrobial tolerance and resistance. The spatially structured environment facilitate the evolution of social behaviors in the biofilm. The social traits displayed by the bacteria are reviewed here with an emphasis on medically relevant biofilms. Emergence of antibiotic resistance has become a global burden and therefore a necessity has arisen to discover novel strategies to target bacteria. Exploiting social behavior by targeting the public goods and weakening the biofilm system by introducing defector cells is also discussed.
Emergence of cooperativity in a model biofilm
Journal of Physics D: Applied Physics, 2017
Evolution to multicellularity from an aggregate of cells involves altruistic cooperation between individual cells, which is in conflict with Darwinian evolution. How cooperation arises and how a cell community resolves such conflicts remain unclear. In this study, we investigated the spontaneous emergence of cell differentiation and subsequent division of labour in evolving cellular metabolic networks. In spatially extended cell aggregates, our findings reveal that resource limitation can lead to the formation of subpopulations and cooperation of cells, and hence multicellular communities. A specific example of our model can explain the recently observed oscillatory growth in Bacillus subtilis biofilms.
The contribution of cell-cell signaling and motility to bacterial biofilm formation
MRS Bulletin, 2011
Many bacteria grow attached to a surface as biofilms. Several factors dictate biofilm formation, including responses by the colonizing bacteria to their environment. Here we review how bacteria use cell-cell signaling (also called quorum sensing) and motility during biofilm formation. Specifically, we describe quorum sensing and surface motility exhibited by the bacterium Pseudomonas aeruginosa, a ubiquitous environmental organism that acts as an opportunistic human pathogen in immunocompromised individuals. P. aeruginosa uses acyl-homoserine lactone signals during quorum sensing to synchronize gene expression important to the production of polysaccharides, rhamnolipid, and other virulence factors. Surface motility affects the assembly and architecture of biofilms, and some aspects of motility are also influenced by quorum sensing. While some genes and their function are specific to P. aeruginosa, many aspects of biofilm development can be used as a model system to understand how bacteria differentially colonize surfaces. Keywords biological; cluster assembly; biomedical Biofilms are an attached growth state of bacteria Relevance of biofilms Biofilms are surface-associated communities of bacteria encased in an extracellular matrix. Biofilms are encountered in almost every imaginable environment. It has been estimated that many bacteria in the environment adopt the biofilm lifestyle (opposed to the free-swimming or planktonic life style). Geesey et al. 1 demonstrated that in the water column of streams in Montana, most bacteria were found associated with surfaces. In industry, biofilms cause many problems, including fouling of ship hulls, promoting corrosion in pipes, and contaminating food processing equipment. They can also be beneficial in industry. For example, they are a key feature of wastewater treatment plants. In the clinic, it has been estimated that biofilms cause up to 60% of all bacterial infections in developed countries. There are several reasons why the biofilm lifestyle is advantageous. One of the primary reasons is that biofilms provide protection from a range of stressors, from antibiotics to host immune response and protozoan grazing. They can also facilitate acquisition of nutrients in cases where the surface is a nutrient source (e.g., a chicken in a poultry processing plant). Biofilms also promote genetic exchange, providing a high local cell density and a stable structured environment for genetic exchange events, such as conjugation and transformation. 2 Because of their widespread importance, there has been an explosion of biofilm-related research in the past 10 years. Scientists and engineers have been probing the molecular mechanisms underpinning biofilm formation and antimicrobial tolerance, while engineers and material scientists have struggled to design surfaces that prevent microbial attachment.
Deciphering links between bacterial interactions and spatial organization in multispecies biofilms
The ISME Journal
Environmental microbes frequently live in multispecies biofilms where mutualistic relationships and co-evolution may occur, defining spatial organization for member species and overall community functions. In this context, intrinsic properties emerging from microbial interactions, such as efficient organization optimizing growth and activities in multispecies biofilms, may become the object of fitness selection. However, little is known on the nature of underlying interspecies interactions during establishment of a predictable spatial organization within multispecies biofilms. We present a comparative metatranscriptomic analysis of bacterial strains residing in triple-species and four-species biofilms, aiming at deciphering molecular mechanisms underpinning bacterial interactions responsible of the remarkably enhanced biomass production and associated typical spatial organization they display. Metatranscriptomic profiles concurred with changes in micro-site occupation in response to the addition/removal of a single species, being driven by both cooperation, competition, and facilitation processes. We conclude that the enhanced biomass production of the four-species biofilm is an intrinsic community property emerging from finely tuned space optimization achieved through concerted antagonistic and mutualistic interactions, where each species occupies a defined micro-site favoring its own growth. Our results further illustrate how molecular mechanisms can be better interpreted when supported by visual imaging of actual microscopic spatial organization, and we propose phenotypic adaptation selected by social interactions as molecular mechanisms stabilizing microbial communities.