Sulfur is one of the common and essential elements of all life. Sulfate, which is a major source of sulfur, plays an important role in synthesizing sulfur-containing amino acids, such as cysteine and methionine, organic compounds essential to all living organisms. Some investigations reported that the assimilatory sulfate reduction pathway (ASRP) involved in cysteine synthesis is crucial to entering bacterial dormancy in pathogens. Our previous investigation reported that the halophilic marine bacterium, Microbulbifer aggregans CCB-MM1T , possesses an ASRP and the dissimilatory sulfate reduction pathway (DSRP). The bacterium might use DSRP to generate energy required for entering its dormant. However, the role of the ASRP in the dormancy of M. aggregans CCB-MM1T was so far unknown. In this study, we found that genes involved in ASRP were downregulated in the dormancy. The disruption of the gene encoding an assimilatory sulfite reductase, cysI, suppressed a completely dormant state under low nutrient conditions. In addition, the cysI mutant showed cell aggregation at the middle-exponential phase under high nutrient conditions, indicating that the mutation might be stimulated to enter the dormancy. The wild-type phenotype of the bacterium was recovered by the addition of cysteine. These results suggested that cysteine concentration may play an important role in inducing the dormancy of M. aggregans.
A novel, rod-shaped, Gram-stain-negative, halophilic and non-motile bacterium, designated CCB-MM1T, was isolated from a sample of estuarine sediment collected from Matang Mangrove Forest, Malaysia. The cells possessed a rod-coccus cell cycle in association with growth phase and formed aggregates. Strain CCB-MM1T was both catalase and oxidase positive, and able to degrade starch. Optimum growth occurred at 30 °C and pH 7.0 in the presence of 2-3 % (w/v) NaCl. The 16S rRNA gene sequence of strain CCB-MM1T showed 98.12, 97.46 and 97.33 % sequence similarity with Microbulbifer rhizosphaerae Cs16bT, Microbulbifer maritimus TF-17T and Microbulbifergwangyangensis GY2T respectively. Strain CCB-MM1T and M. rhizosphaerae Cs16bT formed a cluster in the phylogenetic tree. The major cellular fatty acids were iso-C17 : 1 ω9c and iso-C15 : 0, and the total polar lipid profile consisted of phosphatidylglycerol, phosphatidylethanolamine, phosphoaminolipid, two unidentified lipids, an unidentified glycolipid and an unidentified aminolipid. The major respiratory quinone was ubiquinone Q-8 and the genomic DNA G+C content of the strain was 58.9 mol%. On the basis of the phylogenetic, phenotypic and genotypic data presented here, strain CCB-MM1T represents a novel species of the genus Microbulbifer, for which the name Microbulbiferaggregans sp. nov. is proposed. The type strain is CCB-MM1T (=LMG 29920T=JCM 31875T).
A novel rod-shaped, Gram-stain-negative, strictly aerobic and alginate-degrading marine bacterium, designated CCB-QB4T, was isolated from a surface of algal turf collected from a coastal area of Penang, Malaysia. The cells showed motility by a lateral flagellum. The rod-shaped cells formed long chains end-to-end. Phylogenetic analysis based on the 16S rRNA gene sequence of strain CCB-QB4T showed 94.07, 92.69, 91.52 and 90.90 % sequence similarity to Algibacillus agarilyticus RQJ05T, Catenovulum maritimum Q1T, Catenovulum agarivorans YM01T and Catenovulum sediminis D2T, respectively. Strain CCB-QB4T formed a cluster with A. agarilyticus RQJ05T. Strain CCB-QB4T was catalase-negative, oxidase-positive, and degraded agar, alginate, and starch. Cell growth was observed at 15-40 °C, at pH 7.0-10.0 and in the presence of 1-6 % (w/v) NaCl and glucose. The major fatty acids were summed feature 3 (C16 : 1 ω7c/iso-C15 : 0 2-OH), C16 : 0 and C18 : 1 ω7c. The polar lipids were phosphatidylethanolamine, two unidentified aminolipids, two unidentified glycolipids, an unidentified phospholipid and unidentified lipid. The major respiratory quinone was ubiquinone-8. The genomic DNA G+C content was 46.7 mol%. Based on the phenotypic, chemotaxonomic and phylogenetic data, strain CCB-BQ4T represents a novel species in a new genus, for which the name Saccharobesus litoralis gen. nov., sp. nov. is proposed. The type strain is CCB-QB4T (=JCM 33513T=CCB-MBL 5008T).
Information on the abiotic stress tolerance and ice-ice disease resistance properties of tissue-cultured Kappaphycus alvarezii is scarce and can pose a big hurdle to a wider use of tissue-cultured seaweed in the industry. Here, we reported on a study of seaweed-associated bacteria diversity in farmed and tissue-cultured K. alvarezii, and ice-ice disease resistance and elevated growth temperature tolerance of tissue-cultured K. alvarezii in laboratory conditions. A total of 40 endophytic seaweed-associated bacteria strains were isolated from 4 types of K. alvarezii samples based on their colony morphologies, Gram staining properties and 16S rRNA gene sequences. Bacteria strains isolated were found to belong to Alteromonas sp., Aestuariibacter sp., Idiomarina sp., Jejuia sp., Halomonas sp., Primorskyibacter sp., Pseudoalteromonas sp., Ruegeria sp., Terasakiella sp., Thalassospira sp. and Vibrio sp. Vibrio alginolyticus strain ABI-TU15 isolated in this study showed agar-degrading property when analyzed using agar depression assay. Disease resistance assay was performed by infecting healthy K. alvarezii with 105 cells/mL Vibrio sp. ABI-TU15. Severe ice-ice disease symptoms were detected in farmed seaweeds compared to the tissue-cultured K. alvarezii. Besides disease resistance, tissue-cultured K. alvarezii showed better tolerance to the elevated growth temperatures of 30 and 35 °C. In conclusion, our overall data suggests that tissue-cultured K. alvarezii exhibited better growth performance than farmed seaweeds when exposed to elevated growth temperature and ice-ice disease-causing agent.
Type A chitinases (EC 3.2.1.14), GH family 18, attack chitin ((1 → 4)-2-acetamido-2-deoxy-β-D-glucan) and chito-oligosaccharides from the reducing end to catalyze release of chitobiose (N,N'-diacetylchitobiose) via hydrolytic cleavage of N-acetyl-β-D-glucosaminide (1 → 4)-β-linkages and are thus "exo-chitobiose hydrolases." In this study, the chitinase type A from Serratia marcescens (SmaChiA) was used as a template for identifying two novel exo-chitobiose hydrolase type A enzymes, FbalChi18A and MvarChi18A, originating from the marine organisms Ferrimonas balearica and Microbulbifer variabilis, respectively. Both FbalChi18A and MvarChi18A were recombinantly expressed in Escherichia coli and were confirmed to exert exo-chitobiose hydrolase activity on chito-oligosaccharides, but differed in temperature and pH activity response profiles. Amino acid sequence comparison of the catalytic β/α barrel domain of each of the new enzymes showed individual differences, but ~69% identity of each to that of SmaChiA and highly conserved active site residues. Superposition of a model substrate on 3D structural models of the catalytic domain of the enzymes corroborated exo-chitobiose hydrolase type A activity for FbalChi18A and MvarChi18A, i.e., substrate attack from the reducing end. A main feature of both of the new enzymes was the presence of C-terminal 5/12 type carbohydrate-binding modules (SmaChiA has no C-terminal carbohydrate binding module). These new enzymes may be useful tools for utilization of chitin as an N-acetylglucosamine donor substrate via chitobiose.