Draft Genome Sequence of Leptolyngbya sp. KIOST-1, a Filamentous Cyanobacterium with Biotechnological Potential for Alimentary Purposes

C058 and Other Functional Microorganisms Promote the Synthesis of Extracellular Polymer Substances in Mycelium Biofloc

The mycelium biofloc bioaugmented by Cordyceps strain C058 effectively purifies water, which may be related to the synthesis of extracellular polymer substances. To verify this conjecture, we analyzed the changes in extracellular polymer substances content in the mycelium biofloc under various hydraulic retention times (36 h, 18 h, and 11 h). The microstructure and microflora composition were analyzed using a scanning electron microscope and high-throughput sequencing. The ordinary biofloc without bioaugmentation was taken as a control. The results showed that under the above hydraulic retention time, the extracellular polymer substances contents of the mycelium biofloc were 51.20, 55.89, and 33.84 mg/g, respectively, higher than that of the ordinary biofloc (14.58, 15.72, and 18.19 mg/g). The protein content or the polysaccharide content also followed the same trend. Meanwhile, the sedimentation performance of the mycelium biofloc was better than that of the ordinary biofloc, attributed to the content of the extracellular polymer substances. It is worth noting that C058 is the main biofloc content, which promotes the synthesis of extracellular polymer substances in the mycelium biofloc. Other functional microorganisms in the mycelium biofloc were Janthinobacterium, Phormidium, Leptolyngbya, Hymenobacter, and Spirotrichea, which also promote the synthesis of extracellular polymer substances.

The First Report to Evaluate Safety of Cyanobacterium Leptolyngbya sp. KIOST-1 for Use as a Food Ingredient: Oral Acute Toxicity and Genotoxicity Study

Leptolyngbya sp. KIOST-1 (LK1) is a newly isolated cyanobacterium that shows no obvious cytotoxicity and contains high protein content for both human and animal diets. However, only limited information is available on its toxic effects. The purpose of this study was to validate the safety of LK1 powder. Following Organisation for Economic Co-operation and Development (OECD) guidelines, a single-dose oral toxicity test in Sprague Dawley rats was performed. Genotoxicity was assessed using a bacterial reverse mutation test with Salmonella typhimurium (strains TA98, TA100, TA1535, and TA1537) and Escherichia coli WP2 uvrA, an in vitro mammalian chromosome aberration test using Chinese hamster lung cells, and an in vivo mammalian erythrocyte micronucleus test using Hsd:ICR (CD-1) SPF mouse bone marrow. After LK1 administration (2,500 mg/kg), there were no LK1-related body weight changes or necropsy findings. The reverse mutation test showed no increased reverse mutation upon exposure to 5,000 μg/plate of the LK1 powder, the maximum tested amount. The chromosome aberration test and micronucleus assay demonstrated no chromosomal abnormalities and genotoxicity, respectively, in the presence of the LK1 powder. The absence of physiological findings and genetic abnormalities suggests that LK1 powder is appropriate as a candidate biomass to be used as a safe food ingredient.

Comparative analysis of the total and active bacterial communities in the surface sediment of Lake Taihu

Bacterial communities play crucial roles in the biogeochemical cycle of the surface sediments of freshwater lakes, but previous studies on bacterial community changes in this habitat have mostly been based on the total bacterial community (DNA level), while an exploration of the active microbiota at the RNA level has been lacking. Herein, we analysed the bacterial communities in the surface sediments of Lake Taihu at the DNA and RNA levels. Using MiSeq sequencing and real-time quantification, we found that the sequencing and quantitative results obtained at the RNA level compared with the DNA level were more accurate in responding to the spatiotemporal dynamic changes of the bacterial community. Although both sequencing methods indicated that Proteobacteria, Chloroflexi, Acidobacteria, Nitrospirae, Bacteroidetes and Actinobacteria were the dominant phyla, the co-occurrence network at the RNA level could better reflect the close relationship between microorganisms in the surface sediment. Additionally, further analysis showed that Prochlorococcus and Microcystis were the most relevant and dominant genera of Cyanobacteria in the total and active bacterial communities, respectively; our results also demonstrated that the analysis of Cyanobacteria-related groups at the RNA level was more 'informative'.

Characterization of an Oleaginous Unicellular Green Microalga, Lobosphaera incisa (Reisigl, 1964) Strain K-1, Isolated From a Tidal Flat in the Yellow Sea, Republic of Korea

Microalgae are considered as sustainable resources for biofuel production. However, recently the focus on microalgal research has shifted toward the investigation of high-value metabolites for potential pharmaceutical and nutritional applications. Herein, we report the identification of a novel oleaginous green microalga isolated from the Yellow Sea in Korea. We also describe the morphological, molecular, and biochemical characteristics of this microalga. On the basis of microscopic and genetic analyses, the isolate was classified as Lobosphaera incisa (the strain was designated as K-1), and molecular phylogeny revealed that the isolate distinctly differed from the other known L. incisa strains. The microalga could be cultivated in various commercial culture media under a relatively broad range of pH and temperature conditions. We also did a rough and detailed estimation of the different cellular components in the microalga. The composition of arachidonic acid (C20:4ω6) in the lipids of L. incisa strain K-1 was relatively high, similar to that in other strains, however, the K-1 strain had higher proportions of the ω3 series of fatty acids (FAs), including α-linolenic acid (C18:3ω3) and eicosapentaenoic acid (C20:5ω3), highlighting its uniqueness and strong potential for biotechnological application. To the best of our knowledge, this is the first report on the isolation of L. incisa from Korea as well as from a marine environment; this novel strain might be useful for the production of high-value ω3 and ω6 polyunsaturated fatty acids (PUFAs).

Nitrogen Fixation Genes and Nitrogenase Activity of the Non-Heterocystous Cyanobacterium Thermoleptolyngbya sp. O-77

Cyanobacteria are widely distributed in marine, aquatic, and terrestrial ecosystems, and play an important role in the global nitrogen cycle. In the present study, we examined the genome sequence of the thermophilic non-heterocystous N₂-fixing cyanobacterium, Thermoleptolyngbya sp. O-77 (formerly known as Leptolyngbya sp. O-77) and characterized its nitrogenase activity. The genome of this cyanobacterial strain O-77 consists of a single chromosome containing a nitrogen fixation gene cluster. A phylogenetic analysis indicated that the NifH amino acid sequence from strain O-77 was clustered with those from a group of mesophilic species: the highest identity was found in Leptolyngbya sp. KIOST-1 (97.9% sequence identity). The nitrogenase activity of O-77 cells was dependent on illumination, whereas a high intensity of light of 40 μmol m⁻² s⁻¹ suppressed the effects of illumination.