Living together in biofilms: the microbial cell factory and its biotechnological implications

Spatial Organization Plasticity as an Adaptive Driver of Surface Microbial Communities

Biofilms are dynamic habitats which constantly evolve in response to environmental fluctuations and thereby constitute remarkable survival strategies for microorganisms. The modulation of biofilm functional properties is largely governed by the active remodeling of their three-dimensional structure and involves an arsenal of microbial self-produced components and interconnected mechanisms. The production of matrix components, the spatial reorganization of ecological interactions, the generation of physiological heterogeneity, the regulation of motility, the production of actives enzymes are for instance some of the processes enabling such spatial organization plasticity. In this contribution, we discussed the foundations of architectural plasticity as an adaptive driver of biofilms through the review of the different microbial strategies involved. Moreover, the possibility to harness such characteristics to sculpt biofilm structure as an attractive approach to control their functional properties, whether beneficial or deleterious, is also discussed.

Mutations in the β-Subunit of the RNA Polymerase Impair the Surface-Associated Motility and Virulence of Acinetobacter baumannii

Acinetobacter baumannii is a major cause of antibiotic-resistant nosocomial infections worldwide. In this study, several rifampin-resistant spontaneous mutants obtained from the A. baumannii ATCC 17978 strain that differed in their point mutations in the rpoB gene, encoding the β-subunit of the RNA polymerase, were isolated. All the mutants harboring amino acid substitutions in position 522 or 540 of the RpoB protein were impaired in surface-associated motility and had attenuated virulence in the fertility model of Caenorhabditis elegans The transcriptional profile of these mutants included six downregulated genes encoding proteins homologous to transporters and metabolic enzymes widespread among A. baumannii clinical isolates. The construction of knockout mutants in each of the six downregulated genes revealed a significant reduction in the surface-associated motility and virulence of four of them in the A. baumannii ATCC 17978 strain, as well as in the virulent clinical isolate MAR002. Taken together, our results provide strong evidence of the connection between motility and virulence in this multiresistant nosocomial pathogen.

Biofilm compartmentalisation of the rumen microbiome: modification of fermentation and degradation of dietary toxins

Many deleterious chemicals in plant materials ingested by ruminants produce clinical effects, varying from losses of production efficiency through to death. Many of the effects are insidious, often going unrecognised by animal managers. When secondary plant compounds enter the rumen, they may undergo modification by rumen microbes, which often removes the deleterious compounds, but in specific instances, the deleterious effect may be enhanced. Improved understanding of rumen ecology, particularly concerning the biofilm mode of microbial fermentation, has led to major advances in our understanding of fermentation. In the present review, the potential impact of the physical structuring of the rumen microbiome is discussed in relation to how several economically important secondary plant compounds and other toxins are metabolised by the rumen microbiome and how their toxic effects may be remedied by providing inert particles with a large surface area to weight ratio in the diet. These particles provide additional surfaces for attachment of rumen microorganisms that help alleviate toxicity problems associated with deleterious compounds, including fluoroacetate, mimosine, mycotoxins, cyanoglycosides and hydrogen cyanide. The review first summarises the basic science of biofilm formation and describes the properties of biofilms and their roles in the rumen. It then addresses how biofilms on inert solids and fermentable particulates may assist in detoxification of potentially toxic compounds. A hypothesis that explains how nitrate poisoning may occur as a result of compartmentalisation of nitrate and nitrite reduction in the rumen is included.