SummaryArchaea, one of three major evolutionary lineages of life, encode proteasomes highly related to those of eukaryotes. In contrast, archaeal ubiquitin-like proteins are less conserved and not known to function in protein conjugation. This has complicated our understanding of the origins of ubiquitination and its connection to proteasomes. Here we report two small archaeal modifier proteins, SAMP1 and SAMP2, with a β-grasp fold and C-terminal diglycine motif similar to ubiquitin, that form protein-conjugates in the archaeon Haloferax volcanii. SAMP-conjugates were altered by nitrogen-limitation and proteasomal gene knockout and spanned various functions including components of the Urm1 pathway. LC-MS/MS-based collision-induced dissociation demonstrated isopeptide bonds between the C-terminal glycine of SAMP2 and the ε-amino group of lysines from a number of protein targets and Lys58 of SAMP2 itself, revealing poly-SAMP chains. The widespread distribution and diversity of pathways modified by SAMPylation suggest this type of protein-conjugation is central to the archaeal lineage.

Biofilms are colonies of microbial cells encased in a self-produced organic polymeric matrix and represent a common mode of microbial growth. Microbes growing as biofilm are highly resistant to commonly used antimicrobial drugs. Recently, microbial biofilms have gained prominence because of the increase in infections related to indwelling medical devices (IMD). Candida albicans, the pathogenic fungus which is a major cause of morbidity and mortality in blood stream infections, is the most common fungal pathogen isolated from patients with IMD-associated infections. Biofilm formation by Candida species is believed to contribute to invasiveness of these fungal species. We discuss experimental methods used to study fungal biofilms as well as the biology of biofilm formation by clinically relevant Candida species. Recent advances that are discussed in this review include the role of specific, differentially expressed genes and proteins, quorum sensing molecule in C. albicans biofilms, and the correlation between biofilm formation and fungal pathogenesis.

Candida albicans biofilms form on indwelling medical devices (e.g., denture acrylic or intravenous catheters) and are associated with both oral and invasive candidiasis. Here, we determined whether surface modifications of polyetherurethane (Elasthane 80A [E80A]), polycarbonateurethane, and poly(ethyleneterephthalate) (PET) can influence fungal biofilm formation. Polyurethanes were modified by adding 6% polyethylene oxide (6PEO), 6% fluorocarbon, or silicone, while the PET surface was modified to generate hydrophilic, hydrophobic, cationic, or anionic surfaces. Formation of biofilm was quantified by determining metabolic activity and total biomass (dry weight), while its architecture was analyzed by confocal scanning laser microscopy (CSLM). The metabolic activity of biofilm formed by C. albicans on 6PEO-E80A was significantly reduced (by 78%) compared to that of biofilm formed on the nonmodified E80A (optical densities of 0.054 ؎ 0.020 and 0.24 ؎ 0.10, respectively; P ‫؍‬ 0.037). The total biomass of Candida biofilm formed on 6PEO-E80A was 74% lower than that on the nonmodified E80A surface (0.46 ؎ 0.15 versus 1.76 ؎ 0.32 mg, respectively; P ‫؍‬ 0.003). Fungal cells were easily detached from the 6PEO-E80A surface, and we were unable to detect C. albicans biofilm on this surface by CSLM. All other surface modifications allowed formation of C. albicans biofilm, with some differences in the architecture. Correlation between contact angle and biofilm formation was observed for polyetherurethane substrates (r ‫؍‬ 0.88) but not for PET biomaterials (r ‫؍‬ ؊0.40). This study illustrates that surface modification is a viable approach for identifying surfaces that have antibiofilm characteristics. Investigations into the clinical utility of the identified surfaces are warranted.