Biofilm formation by haloarchaea

Abstract

A fluorescence-based live-cell adhesion assay was used to examine biofilm formation by 20 different haloarchaea, including species of Halobacterium, Haloferax and Halorubrum, as well as novel natural isolates from an Antarctic salt lake. Thirteen of the 20 tested strains significantly adhered (P-value < 0.05) to a plastic surface. Examination of adherent cell layers on glass surfaces by differential interference contrast, fluorescence and confocal microscopy showed two types of biofilm structures. Carpet-like, multi-layered biofilms containing micro- and macrocolonies (up to 50 μm in height) were formed by strains of Halobacterium salinarum and the Antarctic isolate t-ADL strain DL24. The second type of biofilm, characterized by large aggregates of cells adhering to surfaces, was formed by Haloferax volcanii DSM 3757T and Halorubrum lacusprofundi DL28. Staining of the biofilms formed by the strongly adhesive haloarchaeal strains revealed the presence of extracellular polymers, such as eDNA and glycoconjugates, substances previously shown to stabilize bacterial biofilms. For Hbt. salinarum DSM 3754T and Hfx. volcanii DSM 3757T , cells adhered within 1 day of culture and remained viable for at least 2 months in mature biofilms. Adherent cells of Hbt. salinarum DSM 3754T showed several types of cellular appendages that could be involved in the initial attachment. Our results show that biofilm formation occurs in a surprisingly wide variety of haloarchaeal species.

High level of intergenera gene exchange shapes the evolution of haloarchaea in an isolated Antarctic lake

“…Genetic transformation may also be facilitated by the inherently cryogenic stabilizing conditions that are not unlike the cold CaCl 2 conditions used for artificial transformation. Biofilm forming characteristics of prominent members of the DL community may also assist gene exchange (13,15,16). Importantly, given the very low generation rate of DL haloarchaea, genetic sweeps and establishment of new strains by vertical inheritance is expected to occur very slowly.…”

“…It is capable of using a number of different carbon sources including glucose, mannose, acetate and ethanol, providing it with a seemingly versatile heterotrophic metabolism (12). Aside from studies that have noted the ability of H. lacusprofundi, and a recent isolate, tADL (14), to form aggregates and biofilms at either high or low temperatures (13,15,16), the only studies addressing adaptive responses are those linking the production of unsaturated diether membrane lipids to cold adaptation in H. lacusprofundi (3,17).…”

Production of halophilic proteins using Haloferax volcanii H1895 in a stirred-tank bioreactor

“…However, the high tendency of H. volcanii (Albers and Pohlschroder 2009 ;Frols et al 2012 ;Ghosh and Albers 2011 ) to form biofilms prevents the use of this halophilic expression system in stirred-tank bioreactors because these biofilms interfere with sensors during fermentation. The genes Hvo_1033 and Hvo_1034, which encode an ATPase and an integral membrane protein of the pili assembly system, are necessary for biofilm formation (Tripepi et al 2013 ).…”

Characterization of the archaeal community fouling a membrane bioreactor

“…They have even been identified in activated sludge from wastewater treatment plants (Gómez-Silván et al, 2010;Zhang et al, 2011). Some archaeal groups, e.g., Haloarchaea and Crenarchaea, were demonstrated to be capable of adhering to surfaces to form biofilms (Fröls et al, 2012;Koerdt et al, 2010). The quorum sensing (QS) signals, which regulate the biofilm formation processes of bacterial community, were also reported to coordinate the development of archaeal biofilm (Orell et al, 2013).…”