Levan is a fructan-type exopolysaccharide, which is produced by many microbes from sucrose via extracellular levansucrases. The hydrocolloid properties of levan depend on its molecular weight, while it is unknown why and to which extent levan is functionally diverse in dependence of its size. The aim of our study was to get deeper insights into the size-dependent, functional variability of levan. For this purpose, levans of different sizes were produced using the water kefir isolate Gluconobacter albidus TMW 2.1191 and subsequently rheologically characterized. Three levan types could be identified, which are similarly branched, but significantly differ in their molecular size and rheological properties among each other. The smallest levan (< 107 Da) produced without adjustment of the pH exhibited Newton-like flow behavior up to a specific concentration of 25% (w/v). On the contrary, larger levans (> 108 Da) produced at pH ≥ 4.5 were shear-thinning and showed a gel like behavior at ≥ 5% (w/v). A third (intermediate) levan variant was obtained via production in buffers at pH 4.0 and exhibited the properties of a viscoelastic fluid at ≥ 5% (w/v). Our study reveals that the variable size and composition of levan are controllable and more decisive for its functionality than the amount of exerted levan.

Background: Dual function tail tubular proteins (TTP) belonging to the lytic bacteriophages are the interesting group of biologically active enzymes. Surprisingly, apart from their structural function, they are also polysaccharide hydrolyzes destroying bacterial extracellular components. One of the representatives of this group is TTPB from Klebsiella pneumoniae phage – KP32. TTPB hydrolyzes exopolysaccharide (EPS) of Klebsiella pneumoniae and Enterococcus faecalis strain. This depolymerizing feature was associated with the activity to prevent bacterial biofilm formation. TTPB can inhibit biofilm formation by K. pneumoniae, Enterobacter cloacae, Staphylococcus aureus, Enterococcus faecalis and Pseudomonas aeruginosa strains. Moreover, synergistic activity with antibiotic action has been observed, most likely due to depolymerases’ facilitation of contact of antibiotic with bacterial cells. Methods: TTPB was overexpressed in E coli system, purified and tested towards the bacterial strains using agar overlay method. The hydrolytic activity of TTPB was performed using EPSs of K. pneumoniae PCM2713 and E. cloacae ATCC 13047 as the substrates. Next, we determined the reducing sugar (RS) levels in the TTPB/EPS mixtures, regarding the RS amount obtained after acidic hydrolysis. The antibiofilm activity of TTPB has been set down on bacterial biofilm using a biochemical method. Finally, we have demonstrated the synergistic activity of TTPB with kanamycin. Results: For the first time, the hydrolytic activity of TTPB towards bacterial EPSs has been shown. TTPB releases about a half of the whole RS amount of EPSs belonging to K. pneumoniae PCM 2713 and E. cloacae ATCC 13047 strains. 1.12 µM of the phage protein reduces biofilm of both strains by over 60%. Destroying the bacterial biofilm the phage protein improves the antibiotic action increasing kanamycin effectiveness up to four times.

Catalase can decompose hydrogen peroxide in plants under controlled and stressed condi-tions. In a stressed environment, the increase in hydrogen peroxide production makes catalase activity a major defense system for plant growth. The current study was conducted to evaluate the catalase activity of pre-isolated and identified bacterial strains Bacillus aryabhattai (AN30), Bacillus megaterium (AN24), Bacillus megaterium (AN31) and Bacillus megaterium (AN35) and their potential for rice seedlings growth promotion. These strains were characterized for quantita-tive catalase, urease, siderophores, and exopolysaccharides production using LB media. Sub-sequently, the effectiveness of these strains was checked by quantifying the catalase activity in the rhizosphere of rice seedlings. Furthermore, the catalase activity was quantified in the roots and shoots of rice seedlings. Plant growth parameters were also studied in a growth room trial. The strain AN24 showed the maximum catalase activity (1.36 mol cm-1), urease ac-tivity (1.35 mol cm 1), exopolysaccharides (4.20 µg mL-1), and siderophores (2.32%) production in LB media. All tested strains showed significantly higher catalase activity in soil compared to control. Among sole application, strain AN24 showed better results; however, consortium application of strains AN24+AN30+AN35+AN31 showed the maximum increase in catalase ac-tivity in the rhizosphere of rice seedlings. Moreover, consortium application of AN24+AN30+AN31+AN35 resulted in the highest increase in catalase activity, dry biomass of shoots and roots, shoot and root length of rice seedlings. The results showed that a consortium of these Bacillus strains with catalase activity has greater potential to enhance an antioxidant defense system and growth promotion of rice seedlings. However, further experimentation under natural conditions is required before using these strains as potential bioinoculants for improving the rice growth and yield.

Abstract: Rhizobia are soil proteobacteria able to engage in a nitrogen-fixing symbiotic interaction with legumes which involves root rhizobial infection and bacterial invasion of new organs formed by the plant in response to the presence of appropriate bacterial partners. This interaction relies on a complex molecular dialogue between both symbionts. Bacterial N-acetyl-glucosamine oligomers called Nod factors are indispensable in most cases for early steps of the symbiotic interaction. In addition, different rhizobial surface polysaccharides, such as exopolysaccharides (EPS), may also be symbiotically relevant. EPS are acidic polysaccharides located out of the cell with little or no cell association that carry out important roles both in free-life and in symbiosis. EPS production is very complexly modulated and, frequently, co-regulated with that of Nod factors, but the type of co-regulation varies depending on the rhizobial strain. Many studies point out a signalling role of EPS-derived oligosaccharides in root infection and nodule invasion but, in certain symbiotic couples, EPS can be dispensable for a successful interaction. In summary, the complex regulation of the production of rhizobial EPS varies in different rhizobia and the relevance of this polysaccharide in symbiosis with legumes depends on the specific interacting couple.