Bacillus mycoides are known to form rhizoidal colonies on solid medium. In this study, a new strain of B. mycoides, strain Ko01, was isolated from soil. Genetic and growth patterns indicated that this strain belongs to subgroup II of the B. cereus group. Strain Ko01 forms extensive rhizoidal colonies with predictable directions of rotation. The concentration of the agar, and not the chemical composition, altered the direction of the colony rotation, switching from counterclockwise to clockwise. Agar concentration-dependent switching of rotation direction was unique to strain Ko01 and was not seen in colonies of other B. mycoides strains that were tested. Factors affecting colony chirality patterns appeared to be variable among B. mycoides strains. This feature can be used for the classification of B. mycoides strains.
This paper presents a study of the magnitude and mechanism of impeding the emergent spore germination of Bacillus subtilis (non-hemolytic strain) and Bacillus licheniformis (hemolytic strain) under the action of soybean glycinin and its basic subunit (BS). Incubating B. licheniformis spores with 100 μg/ml of glycinin or BS at 35°C for 24 h totally prevented the hemolytic activity associated with the emergent vegetative cells on blood agar during 3–5 days of incubation at 35°C in contrast to the control. Glycinin and BS (100 μg/ml) also resulted in the leakage of 70 and 73% of the initially germinating spore contents of A260 absorbing materials of the two bacterial species after 2 h of incubation at 35°C, respectively. Increasing the concentration of glycinin and BS up to 400 μg/ml increased the germinating spore leakage to 83 and 88%, respectively. Spore germination in Muller Hinton Broth containing glycinin and BS (100 μg/ml) was practically nil after 4 days of incubation at 35°C. Supplementing milk preheated at 80°C/5 min with both glycinin and BS kept the final vegetative cell counts down to about 30 and 20% of the corresponding control, respectively, after 50 days of storage at 4°C. Both light, and transmission electron, microscopy images revealed significant morphological and structural distorting changes in BS-treated spores of B. licheniformis.
Quorum sensing (QS) is a cell-to-cell communication mechanism through which microbial cells communicate and regulate their wide variety of biological activities. N-acyl homoserine lactones (AHLs) are considered to be the most important QS signaling molecules produced by several Gram-negative bacteria. The present study aimed to screen the AHLs-producing bacteria from spoiled vacuum-packaged refrigerated turbot (Scophthalmus maximus) by biosensor assays, and the profiles of AHLs produced by these bacteria were determined using reversed-phase thin-layer chromatography (RP-TLC) and gas chromatography-mass spectrometry (GC-MS). Effects of exogenous AHLs and QS inhibitor (QSI) on the phenotypes (i.e., extracellular proteolytic activity and biofilm formation) of the AHLs-producing bacteria were also evaluated. Our results demonstrated that eight out of twenty-two isolates were found to produce AHLs. Three of the AHLs-producing isolates were identified as Serratia sp., and the other five were found to belong to the family of Aeromonas. Two isolates (i.e., S. liquefaciens A2 and A. sobria B1) with higher AHLs-producing activities were selected for further studies. Mainly, RP-TLC and GC-MS analysis revealed three AHLs, i.e., 3-oxo-C6-HSL, C8-HSL and C10-HSL were produced by S. liquefaciens A2, while five AHLs, i.e., C4-HSL, C6-HSL, C8-HSL, C10-HSL, and C12-HSL, were produced by A. sobria B1. Moreover, production of AHLs in both bacterial strains were found to be density-dependent, and the AHLs activity reached a maximum level in their middle logarithmic phase and decreased in the stationary phase. The addition of exogenous AHLs and QSI decreased the specific protease activity both of the Serratia A2 and Aeromonas B1. Exogenous AHLs inhibited the biofilm formation of Serratia A2 while it enhanced the biofilm formation in Aeromonas B1. QSI inhibited the specific protease activity and biofilm formation in both bacterial strains.
Z. mobilis cell immobilization has been proposed as an effective means of improving ethanol production. In this work, polystyrene and corn silk were used as biofilm developmental matrices for Z. mobilis ethanol production with rice straw hydrolysate as a substrate. Rice straw was hydrolyzed by dilute sulfuric acid (H2SO4) and enzymatic hydrolysis. The final hydrolysate contained furfural (271.95 ± 76.30 ppm), 5-hydroxymethyl furfural (0.07 ± 0.00 ppm), vanillin (1.81 ± 0.00 ppm), syringaldehyde (5.07 ± 0.83 ppm), 4-hydroxybenzaldehyde (4-HB) (2.39 ± 1.20 ppm) and acetic acid (0.26 ± 0.08%). Bacterial attachment or biofilm formation of Z. mobilis strain TISTR 551 on polystyrene and delignified corn silk carrier provided significant ethanol yields. Results showed up to 0.40 ± 0.15 g ethanol produced/g glucose consumed when Z. mobilis was immobilized on a polystyrene carrier and 0.51 ± 0.13 g ethanol produced/g glucose consumed when immobilized on delignified corn silk carrier under batch fermentation by Z. mobilis TISTR 551 biofilm. The higher ethanol yield from immobilized, rather than free living, Z. mobilis could possibly be explained by a higher cell density, better control of anaerobic conditions and higher toxic tolerance of Z. mobilis biofilms over free cells.
To obtain lactic acid bacteria that scavenge environmental hydrogen peroxide, we developed a specialized enrichment medium and successfully isolated Pediococcus pentosaceus Be1 strain from a fermented food. This strain showed vigorous environmental hydrogen peroxide scavenging activity over a wide range of hydrogen peroxide concentrations. High Mn-catalase and NADH peroxidase activities were found in the cell-free extract of the P. pentosaceus Be1 strain, and these two hydrogen peroxide scavenging enzymes were purified from the cell-free extract of the strain. Mn-catalase has been purified from several microorganisms by several researchers, and the NADH peroxidase was first purified from the original strain in this report. After cloning the genes of the Mn-catalase and the NADH peroxidase, the deduced amino acid sequences were compared with those of known related enzymes.
To improve the thermostability of xylanase XynZF-2 from Aspergillus niger XZ-3S, a disulfide bridge was introduced in the N-terminal domains by site-directed mutagenesis (V1C and E27C). Simultaneously, the active sites of XynZF-2 were predicted by bioinformatics software and verified by site-directed mutagenesis (E103D and E194D). The mutated active sites xynED- and the mutated disulfide bridge xynDC-encoding genes were constructed and expressed in Escherichia coli BL21 (DE3). Compared to the native xylanase, it was found that the residual activity of the mutated XynED was 0.17%. The optimum temperature of the variant XynDC was increased to 45°C from 40°C of XynZF-2. After treatment at 40°C for 60 min, the variant XynDC retained 66.77% of their original activity, while the XynZF-2 retained about 44.36% residual activity. t1/245°C of the variant XynDC also increased from 7 min to 14 min. The results of the mutated xylanases indicated that the active center of XynZF-2 mainly consisted of two catalytic residues (Glu103 and Glu194), and the introduction of a disulfide bridge in the N-terminal domains can improve the thermostability of XynZF-2.
Acyl transfer activity (ATA) of amidase transfers an acyl group of different amides to hydroxylamine to form the corresponding hydroxamic acid. Bacterial isolate BR-1 was isolated from cyanogenic plant Cirsium vulgare rhizosphere and identified as Pseudomonas putida BR-1 by 16S rDNA sequencing. This organism exhibited high ATA for the biotransformation of N-substituted aromatic amide to the corresponding hydroxamic acid. Optimization of media, tryptone (0.6%), inducer, pH 8.5, and a growth temperature 25°C for 56 h, resulted in a 7-fold increase in ATA. Further, Response Surface Methodology (RSM) and multiple feeding approach (20 mM after 14 h) of inducer led to a 29% enhancement of ATA from this organism. The half life (t1/2) of this enzyme at 50°C and 60°C was 3 h and 1 h, respectively. The ATA of amidase of Pseudomonas putida BR-1 makes it a potential candidate for the production of a variety of N-substituted aromatic hydroxamic acid.
Sirtuin is a protein with an enzymatic activity of NAD+-dependent protein deacetylation. It was first identified in yeast and its homologous genes have been widely found in various organisms. In bacteria, sirtuin gene was first described as cobB, encoding a cobalamin processing enzyme; and later its potential involvement in regulating acetylation levels of metabolic enzymes, transcription factors, chemotactic proteins and others have been reported. In order to study its physiological relevance in probiotic lactic acid bacteria, we analyzed the whole genome of three L. paracasei strains. All strains tested had sirtuin homolog genes designated hereby as sirA, and one of them had an additional gene designated as sirB. Following confirmation of their coding sequences by individual gene cloning, corresponding recombinant proteins have been generated and purified. The enzymatic characterization revealed that the intrinsic NAD+-dependent deacetylation activity of LpSirA (protein encoded by sirA) is comparable to human SIRT1. Furthermore, by blocking sirtuin activity using nicotinamide in vivo, together with an in vitro deacetylation reaction using recombinant LpSirA, we identified one of the target proteins in the lactic acid bacteria as the 30S ribosomal protein S4 (rpsD product).