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Ulvan is the main polysaccharide component of the Ulvales (green seaweed) cell wall. It is composed of disaccharide building blocks comprising 3-sulfated rhamnose linked to D-glucuronic acid (GlcUA), L-iduronic acid (IdoUA), or D-xylose (Xyl). The degradation of ulvan requires ulvan lyase, which catalyzes the endolytic cleavage of the glycoside bond between 3-sulfated rhamnose and uronic acid according to a ␤-elimination mechanism. The first characterized ulvan lyase was identified in Nonlabens ulvanivorans, an ulvanolytic bacterial isolate. In the current study, we have identified and biochemically characterized novel ulvan lyases from three Alteromonadales isolated bacteria. Two homologous ulvan lyases (long and short) were found in each of the bacterial genomes. The protein sequences have no homology to the previously reported ulvan lyases and therefore are the first representatives of a new family of polysaccharide lyases. The enzymes were heterologously expressed in Escherichia coli to determine their mode of action. The heterologous expressed enzymes were secreted into the milieu subsequent to their signal sequence cleavage. An endolytic mode of action was observed and studied using gel permeation chromatography and 1 H NMR. In contrast to N. ulvanivorans ulvan lyase, cleavage occurred specifically at the GlcUA residues. In light of the genomic context and modular structure of the ulvan lyase families identified to date, we propose that two ulvan degradation pathways evolved independently.

Bacterial urinary tract infections resulting from prolonged patient catheterization have become a major health problem. One of the major issues is bacterial resistance to antibiotic treatments due to biofilm formation inside the catheters, thus enhancing the search for alternative treatments. In the present study, a device containing a piezo element capable of transmitting low-frequency surface acoustic waves (SAW) onto the indwelling catheter was used. The SAW were able to eradicate biofilm-residing bacteria by >85% when applied simultaneously with an antibiotic in three clinically relevant species, viz. Escherichia coli, Staphylococcus epidermidis and Pseudomonas aeruginosa. Moreover, transcriptome analysis revealed that SAW can alter the transcription pattern of P. aeruginosa, suggesting that this signal can be specifically sensed by the bacterium.

Ulvan is a major cell wall component of green algae of the genus Ulva and some marine bacteria encode enzymes that can degrade this polysaccharide. The first ulvan degrading lyases have been recently characterized and several putative ulvan lyases have been recombinantly expressed, confirmed as ulvan lyases and partially characterized. Two families of ulvan degrading lyases, PL24 and PL25, have recently been established. The PL24 lyase LOR_107 from the bacterial Alteromonadales sp. strain LOR degrades ulvan endolytically, cleaving the bond at the C4 of a glucuronic acid. However, the mechanism and LOR_107 structural features involved are unknown. We present here the crystal structure of LOR_107, representing the first PL24 family structure. We found that LOR_107 adopts a seven-bladed β-propeller fold with a deep canyon on one side of the protein. Comparative sequence analysis revealed a cluster of conserved residues within this canyon, and site-directed mutagenesis disclosed several residues essential for catalysis. We also found that LOR_107 uses the His/Tyr catalytic mechanism, common to several PL families. We captured a tetrasaccharide substrate in the structures of two inactive mutants, which indicated a two-step binding event, with the first substrate interaction near the top of the canyon coordinated by Arg-320, followed by sliding of the substrate into the canyon toward the active-site residues. Surprisingly, the LOR_107 structure was very similar to that of PL25 family PLSV_3936, despite only ~14% sequence identity between the two enzymes. On the basis of our structural and mutational analyses, we propose a catalytic mechanism for LOR_107 that differs from the typical His/Tyr mechanism.Ulvan is one of the two major cell wall components of marine green algae (genus Ulva and Enteromorpha). It is a complex sulfated polysaccharide composed mainly of 3-sulfated rhamnose (Rha3S), glucuronic acid (GlcA), iduronic acid (IdoA) and xylose (1). The common disaccharide repetitive units within the ulvan polysaccharides are [→4)-β-D-GlcA-(1→4)-α-LRha3S-(1→] called type A ulvanobiourinic-3-sulfate (A 3S ) and [→4)-α-L-IdoA-(1→4)-α-LRha3S(1→] called type B ulvanobiouronic-3-sulfate (B 3S ) (1) (Schema 1). The presence of iduronic acid and sulfated rhamnose differentiates ulvan from other polysaccharides of marine origin and displays similarity with mammalian glycosaminoglycans such as chondroitin sulfate and hyaluronic acid. This distinctive chemical feature makes ulvan an attractive candidate for various biomedical, nanobiotechnological and drug delivery applications (2-6).Polysaccharides containing uronic acid sugars can be degraded by enzymes utilizing a β-http://www.jbc.org/cgi/doi/10.1074/jbc.RA117. (PLs). They utilize a β-elimination mechanism to cleave the oxygenaglycone bond by abstracting the C5 proton, which results in the formation of an unsaturated 4-deoxy-L-threo-hex-4-enopyranosiduronic acid (ΔUA) at the non-reducing end of the oligosaccharide product (7). These enzymes are presently classified into 26 s...

Here we report the draft genome sequence of the bacterium Nonlabens ulvanivorans, which was recently isolated. To our knowledge, this is the first published genome of a characterized ulvan-degrading bacterium. Revealing the ulvan utilization pathways may provide access to a vast marine biomass source that has yet to be exploited.