Microorganisms predominantly exist in sessile communities rather than as free-living planktonic cells. These sessile communities develop on all surfaces in aqueous environments. Bacteria are now known to organise themselves in complex surface attached micro-colonies, and other surface specific morphological structures, in which cells undergo differentiation as part of a complex development program. Such differentiated surface communities, in which bacterial cells are embedded in a macromolecular containing matrix, are called biofilms. An improved understanding of the biofilm differentiation and development programs in bacteria has several profound implications:
(i) There are similarities between biofilm formation and development in "single cell" prokaryotes and higher multicellular bacteria, such as those with fruiting bodies and spore formation, as well as cellular differentiation in multicellular prokaryotes. Inter-cellular signalling mediates core events such as apoptosis, maturation and ageing. Cell-cell signalling may involve high density dependant autoinduction systems for the coordination of genes involved in colonization, differentiation and virulence. Such quorum sensing systems are employed by a large number of bacteria. Moreover, intracellular signals, such as c-di-GMP and autocidal differentiating inducers, such as phage and autotoxic proteins are also key for successful development of biofilms. Studies of bacterial biofilms are dramatically increasing our understanding of cell-cell signalling systems and of differentiation event in multicellular organisms.
The CMBB supports several research projects on biofilm formation by environmentally as well as medically relevant bacteria. Particular objectives include assessment of the precise roles of signals in the temporal and spatial expression of biofilm specific genes, cellular differentiation, apoptosis, ageing and dispersal of the biofilm cells.
(ii) Most ecological studies have focused on free-living bacteria and there is a dearth of information on the ecological role of bacteria in biofilms. Fundamental questions on biofilm biology being addressed include bacterial productivity, elemental cycling, bioremediation processes and associations with higher organisms. The CMBB runs an extensive program on the role of surface colonizing bacteria on marine plants and sessile animals. The program addresses the extent of microbial diversity in the environment, identification of novel communication systems and bioactives and the role of bacteria in preventing or inducing settlement of colonising prokaryotes or eukaryotes on sessile marine hosts. Whole community sequencing and functional metagenomics are key experimental approaches to undertake such studies(see
Environmental Genetics).
(iii) Formation of large biofilm communities and the protective role of biofilms against killing of bacterial cells by conventional antimicrobial treatments present significant problems in industry and in the treatment of bacterial infections. Several basic research projects as well as applied R and D ventures for novel antibiofilm treatments have been initiated. The CMBB has developed advanced
quorum sensing blocking technologies, following the identification of effective marine QSBs and structure function based
optimization of lead compounds.
