Kunihiro Okano

Detection and sequencing of the microcystin LR-degrading gene, mlrA, from new bacteria isolated from Japanese lakes

mlrA is the only microcystin-degrading gene detected in Sphingomonas sp. MJ-PV. The gene has an extremely rare nucleotide sequence and homologous genes have not yet been discovered in the DNA database. We discovered the existence of a gene homologous to mlrA in new microcystin-degrading bacteria, MD-1 and Y2. These strains possessed mlrA homologues, and the identities of the genes of MD-1 and Y2 with the corresponding MJ-PV exceeded 98% and 84%, respectively. On the other hand, the mlrA gene was not detected in laboratory strains of the closely related Sphingomonas spp. strains employing hemi-nested polymerase chain reaction detection using two primer sets. Although the microcystin-degrading bacteria were closely related strains, they did not cluster together as the same species. We can conclude that the mlrA gene is conserved in three different bacterial species, and it is unique to microcystin degraders but not to the genus Sphingomonas.

Characteristics of a Microcystin-Degrading Bacterium under Alkaline Environmental Conditions

The pH of the water associated with toxic blooms of cyanobacteria is typically in the alkaline range; however, previously only microcystin-degrading bacteria growing in neutral pH conditions have been isolated. Therefore, we sought to isolate and characterize an alkali-tolerant microcystin-degrading bacterium from a water bloom using microcystin-LR. Analysis of the 16S rRNA gene sequence revealed that the isolated bacterium belonged to the genus Sphingopyxis, and the strain was named C-1. Sphingopyxis sp. C-1 can grow; at pH 11.0; however, the optimum pH for growth was pH 7.0. The microcystin degradation activity of the bacterium was the greatest between pH 6.52 and pH 8.45 but was also detected at pH 10.0. The mlrA homolog encoding the microcystin-degrading enzyme in the C-1 strain was conserved. We concluded that alkali-tolerant microcystin-degrading bacterium played a key role in triggering the rapid degradation of microcystin, leading to the disappearance of toxic water blooms in aquatic environments.

Enzymatic pathway for biodegrading microcystin LR in Sphingopyxis sp. C-1

The mlr gene cluster consisting of mlrA, mlrB, mlrC, and mlrD is involved in the degradation of the cyanobacterial toxin microcystin. However, it is unclear which degradation intermediates are metabolized by MlrB and MlrC. To address these questions, we constructed recombinant Escherichia coli to overproduce MlrB and MlrC from Sphingopyxis sp. C-1, and determined which intermediates were degraded in cell-free extracts. The cell-free extract containing MlrB degraded linearized microcystin-LR, giving rise to a tetrapeptide. The cell-free extract of MlrC degraded linearized microcystin-LR and also degraded the tetrapeptide to the amino acid Adda. These results indicate that linearized microcystin-LR is degraded by both MlrB and MlrC, and tetrapeptide is degraded by specifically by MlrC in Sphingopyxis sp. C-1.

Whole Genome Sequence of the Non-Microcystin-Producing Microcystis aeruginosa Strain NIES-44

ABSTRACT Microcystis aeruginosa is a typical algal bloom-forming cyanobacterium. This report describes the whole-genome sequence of a non-microcystin-producing strain of Microcystis aeruginosa, NIES-44, which was isolated from a Japanese lake.

Whole-Genome Sequence of the Microcystin-Degrading Bacterium Sphingopyxis sp. Strain C-1

ABSTRACT This report describes the whole-genome sequence of an alkalitolerant microcystin-degrading bacterium, Sphingopyxis sp. strain C-1, isolated from a lake in China.

Complete Genome Sequence of the Unclassified Iron-Oxidizing, Chemolithoautotrophic Burkholderiales Bacterium GJ-E10, Isolated from an Acidic River

ABSTRACT Burkholderiales bacterium GJ-E10, isolated from the Tamagawa River in Akita Prefecture, Japan, is an unclassified, iron-oxidizing chemolithoautotrophic bacterium. Its single circular genome, consisting of 3,276,549 bp, was sequenced by using three types of next-generation sequencers and the sequences were then confirmed by PCR-based Sanger sequencing.

Adsorption and Biodegradation Characteristics of Musty Odorous Compounds, 2-Methylisoborneol and Geosmin

Adsorption and biodegradation characteristics of musty odorous compounds, methylisoborneol (MIB) and geosmin were examined using activated carbon and nonadsorbing cellulose material as biofi lm carriers. Pseudomonas sp. capable of MIB degradation was used as a biofi lm-forming bacterium for the carriers. In the isotherm tests for MIB and geosmin, MIB was effi ciently removed by two types of carbon, and the carbon with wider surface area showed higher removal effi ciency. However, there was no removal effi ciency in the two types of cellulose with diff erent pore size of μm and μm. In the removal eff ects of MIB by carbon and cellulose carriers with Pseudomonas sp., the carbon formed biofi lm viz. biological activated carbon (BAC) could highly degrade MIB by . %, while cellulose-carrier showed MIB removal with . % within hrs, comparing with obvious less removal of . % by the planktonic degrader in water solution. It was found that Pseudomonas sp. aggregated on the carrier could considerably enhance MIB degradation whether the biofi lm carrier was adsorption or not.

Transfer of cyanobacterial carbon to a higher trophic-level fish community in a eutrophic lake food web: fatty acid and stable isotope analyses

The dietary utilization of cyanobacterial carbon by fish communities is poorly understood. We examined the transfer of cyanobacterial carbon to fish in a eutrophic lake using fatty acid biomarkers and measuring the stable carbon isotope ratios of fatty acid and bulk nitrogen. We collected five species of fish (Hypomesus nipponensis, Carassius sp., Cyprinus carpio, Tridentiger brevispinis, and Gymnogobius castaneus) as well as the seston from June to November 2016 from Lake Hachiro, Japan. Cyanobacterial blooms were observed from August to October. From June to August, cyanobacterial fatty acid biomarkers (18:2ω6 and 18:3ω3) accounted for only 1.4–4.3% of total fatty acids in these fish species, indicating a low contribution of cyanobacteria to fish diets during this period. However, the contribution of the cyanobacterial fatty acid biomarkers in these fish species increased sharply in September (10.5–17.1%), except in second-year H. nipponensis. In September, the stable carbon isotope ratios of 18:3ω3 in these fish species were almost equivalent to those in the seston, which was primarily composed of cyanobacteria. The trophic positions of the collected fish species ranged from 1.6 to 3.4, based on their stable nitrogen isotope values, indicating that some fish ingested cyanobacteria directly, while others acquired cyanobacteria indirectly, through the food chain. These findings indicate that cyanobacterial carbon is transferred up the food chain in eutrophic lake ecosystems with cyanobacterial blooms.

Whole-Genome Sequences of Two Manganese(II)-Oxidizing Bacteria, Bosea sp. Strain BIWAKO-01 and Alphaproteobacterium Strain U9-1i

ABSTRACT This report describes the whole-genome sequences of two Mn(II)-oxidizing bacteria, filamentous Mn oxide microparticle-forming Bosea sp. strain BIWAKO-01 and alphaproteobacterium strain U9-1i.