Firm but Slippery Attachment of Deinococcus geothermalis

Abstract

Bacterial biofilms impair the operation of many industrial processes. Deinococcus geothermalis is efficient primary biofilm former in paper machine water, functioning as an adhesion platform for secondary biofilm bacteria. It produces thick biofilms on various abiotic surfaces, but the mechanism of attachment is not known. High-resolution field-emission scanning electron microscopy and atomic force microscopy (AFM) showed peritrichous adhesion threads mediating the attachment of D. geothermalis E50051 to stainless steel and glass surfaces and cell-to-cell attachment, irrespective of the growth medium. Extensive slime matrix was absent from the D. geothermalis E50051 biofilms. AFM of the attached cells revealed regions on the cell surface with different topography, viscoelasticity, and adhesiveness, possibly representing different surface layers that were patchily exposed. We used oscillating probe techniques to keep the tip-biofilm interactions as small as possible. T also formed tenacious biofilms. This paper shows that D. geothermalis has firm but laterally slippery attachment not reported before for a nonmotile species.Bacteria growing as biofilms are more resistant to many antimicrobial agents than free-swimming bacteria, a characteristic of the biofilms resulting in, e.g., persistent infections of the human body and troublesome biofilms in water distribution systems and in industrial processes (7,17,20,32). Paper mills use biocides to control microbial growth, but this has not eliminated biofilms, which may detach from surfaces, impairing operation of the machines or causing defects such as holes and colored spots in the paper products (4,16,29,30). Not all bacteria form biofilms; some machines run with 10 5 to 10 8 CFU of free-swimming bacteria ml of circulating water Ϫ1 with no process disturbances. We recently showed Deinococcus geothermalis to be an efficient primary biofilm former in paper machine water (30), functioning as an adhesion platform for secondary biofilm bacteria, e.g., Bacillus species (16). D. geothermalis forms thick biofilms on various abiotic surfaces, such as stainless steel and polystyrenes (16), glass, and polyethene, but the mechanism of attachment is not known.D. geothermalis possesses no flagella or pili for attachment (11) and does not produce large amounts of slime. Bacteria of the genus Deinococcus, including the well-studied D. radiodurans, are known to be highly resistant towards radiation and desiccation (18). According to Makarova et al. (18), it is likely that the extreme radiation resistance evolved in response to chronic exposure to nonradioactive forms of DNA damage, readily inflicted by, e.g., nonstatic environments such as cycles of desiccation and hydration. Such conditions often prevail in biofilms near the air-water interface. Orthologs of almost all known genes involved in different stress responses in other bacteria are present in D. radiodurans (18). All of these properties can contribute to the potential of D. geothermalis for biofouling. We investigated the s...

Characterization of Adhesion Threads of Deinococcus geothermalis as Type IV Pili

“…3) and, therefore, the images indicate that the surface appendages of live cells are the location of glycoconjugates both in individual surface-adhered cells and inside biofilm colonies. Previous studies (18,29) showed that an extensive slime matrix is absent in D. geothermalis biofilms, which discards the possibility that lectins may bind matrix exopolysaccharides. According to the manufacturer, Amaranthus caudatus lectin has specificity for oligosaccharides containing galactosyl Gal␤(1,3)GalNAc ␣-units.…”

“…Although Deinococcaceae are considered nonmotile, a pre- vious study described the ability of D. geothermalis E50051 to slide away from mechanical stress (18). Similarly, adhesion pili from uropathogenic Escherichia coli are capable of a structural transition which allows the pilus to unravel and extend plastically (3).…”

“…However, adhesion of D. geothermalis seems to occur in the absence of either of these (18,29). Another attachment mode by means of pili has been described for several gram-negative pathogenic bacteria, including, for example, Neisseria meningitidis, N. gonorrhoeae (22,36), and Pseudomonas aeruginosa (38), and for some grampositive bacteria, such as Enterococcus faecalis (11), Actinomyces spp.…”

“…It forms tenuous biofilms on abiotic surfaces and is difficult or impossible to remove from the surfaces using industrial washing procedures (18). The attachment of D. geothermalis involves thread-like structures that connect the cells to the abiotic surface while allowing sliding movement, to escape mechanical stress (18).…”

Biofilm Cohesiveness Measurement Using a Novel Atomic Force Microscopy Methodology

“…Drying is expected to significantly change the strength and overall character of a biofilm; therefore, measurements made on dry biofilm must be interpreted and applied carefully. A few AFM studies have investigated biofilm properties, such as interaction and attachment to surfaces under aqueous conditions (5,21). Yet, there is a real need to expand this work to study additional properties of whole biofilms under aqueous conditions.…”