Cochlodiniinecator piscidefendens gen. nov., sp. nov., an algicidal bacterium against the ichthyotoxic dinoflagellate Cochlodinium polykrikoides

Algicidal activity of a novel bacterium, Qipengyuania sp. 3-20A1M, against harmful Margalefidinium polykrikoides: Effects of its active compound

Margalefidinium polykrikoides causes significant economic losses in the aquaculture industry by red tide formation. Algicidal bacteria have attracted research interests as a potential bloom control approach without secondary pollution. Qipengyuania sp. 3-20A1M, isolated from surface seawater, exerted an algicidal effect on M. polykrikoides. However, it exhibited a significantly lower algicidal activity toward other microalgae. It reduced photosynthetic efficiency of M. polykrikoides and induced lipid peroxidation and cell disruption. The growth inhibition of M. polykrikoides reached 64.9 % after 24 h of co-culturing, and expression of photosynthesis-related genes was suppressed. It killed M. polykrikoides indirectly by secreting algicidal compounds. The algicide was purified and identified as pyrrole-2-carboxylic acid. After 24 h of treatment with pyrrole-2-carboxylic acid (20 μg/mL), 60.8 % of the M. polykrikoides cells were destroyed. Overall, our results demonstrated the potential utility of Qipengyuania sp. 3-20A1M and its algicidal compound in controlling M. polykrikoides blooms in the marine ecosystem.

Mucilaginibacter aquariorum sp. nov., Isolated from Fresh Water

A Gram-stain-negative, rod-shaped bacterial strain, JC4^T, was isolated from a freshwater sample and determined the taxonomic position. Initial identification based on 16S rRNA gene sequences revealed that strain JC4^T is affiliated to the genus Mucilaginibacter with a sequence similarity of 97.97% to Mucilaginibacter rigui WPCB133^T. The average nucleotide identity and digital DNA-DNA hybridization values between strain JC4^T and Mucilaginibacter species were estimated below 80.92% and 23.9%, respectively. Strain JC4^T contained summed feature 3 (C_16:1 ω7c and/or C_16:1 ω6c) and iso-C_15:0 as predominant cellular fatty acids. The dominant polar lipids were identified as phosphatidylethanolamine, one unidentified aminophospholipid, one unidentified phospholipid, and two unidentified lipids. The respiratory quinone was MK-7. The genomic DNA G+C content of strain JC4^T was determined to be 42.44%. The above polyphasic evidences support that strain JC4^T represents a novel species of the genus Mucilaginibacter, for which the name Mucilaginibacter aquariorum sp. nov. is proposed. The type strain is JC4^T (= KCTC 92230^T = LMG 32715^T).