The Mitochondrial Genome of the Sea Anemone Stichodactyla haddoni Reveals Catalytic Introns, Insertion-Like Element, and Unexpected Phylogeny

A hallmark of sea anemone mitochondrial genomes (mitogenomes) is the presence of complex catalytic group I introns. Here, we report the complete mitogenome and corresponding transcriptome of the carpet sea anemone Stichodactyla haddoni (family Stichodactylidae). The mitogenome is vertebrate-like in size, organization, and gene content. Two mitochondrial genes encoding NADH dehydrogenase subunit 5 (ND5) and cytochrome c oxidase subunit I (COI) are interrupted with complex group I introns, and one of the introns (ND5-717) harbors two conventional mitochondrial genes (ND1 and ND3) within its sequence. All the mitochondrial genes, including the group I introns, are expressed at the RNA level. Nonconventional and optional mitochondrial genes are present in the mitogenome of S. haddoni. One of these gene codes for a COI-884 intron homing endonuclease and is organized in-frame with the upstream COI exon. The insertion-like orfA is expressed as RNA and translocated in the mitogenome as compared with other sea anemones. Phylogenetic analyses based on complete nucleotide and derived protein sequences indicate that S. haddoni is embedded within the family Actiniidae, a finding that challenges current taxonomy.

Antibacterial and Antibiofilm Potential of Sea Anemone (Stichodactyla haddoni)-Isolated Vibrio (V. parahaemolyticus and V. alginolyticus), and Pseudoalteromonas (P. gelatinilytica and P. piscicida) Against Staphylococcus aureus and Pseudomonas aeruginosa

Background: Staphylococcus aureus and Pseudomonas aeruginosa are important human bacterial pathogens, which are resistant to several antibiotics. One of the main causes of their resistance is the ability of biofilm formation. Objectives: The present study aimed to evaluate the antibacterial and antibiofilm activity of the extracts of Vibrio parahaemolyticus, V. alginolyticus, Pseudoalteromonas gelatinilytica, and Pseudoalteromonas piscicida isolated from sea anemone (Stichodactyla haddoni) against S. aureus and P. aeruginosa. Methods: Four isolated bacteria were identified using biochemical and molecular identification methods, and their extracts were obtained by mixing the cell-free supernatants from their old broth culture using ethyl acetate and methanol as the solvents. The agar well-diffusion and micro-dilution methods were also applied to determine the antibacterial activity, minimum bactericidal concentration (MBC), and minimum inhibitory concentration (MIC) of the extracts. The ability of the extracts to inhibit biofilm formation and disrupt the preformed biofilm of the pathogens was attained through crystal violet staining in 96-well microtiter plates. To determine the nature of the extracts, they were exposed to protease enzyme, and the antibiofilm activity was compared with the untreated extracts. Results: The extracts of the four isolated bacteria inhibited bacterial growth and biofilm formation and disrupted the preformed biofilm of S. aureus (MIC = BIC = 600 µg/mL) and P. aeruginosa (MIC = BIC = 300 µg/mL). In addition, the active compounds of the extracts with antibiofilm activities were mainly proteases. Conclusions: According to the results, V. parahaemolyticus, V. alginolyticus, P. gelatinilytica, and P. piscicida had antibacterial and antibiofilm potential against S. aureus and P. aeruginosa, and their extract could also be further analyzed as an alternative to antibiotics.

Reproduction in Urbanised Coastal Waters: Shallow-Water Sea Anemones (Entacmaea quadricolor and Stichodactyla haddoni) Maintain High Genetic Diversity and Panmixia

Sea anemones are sedentary marine animals that tend to disperse via planktonic larvae and are predicted to have high population connectivity in undisturbed habitats. We test whether two sea anemone species living in two different tidal zones of a highly disturbed marine environment can maintain high genetic connectivity. More than 1000 loci with single-nucleotide polymorphisms (SNPs) were obtained with double-digest RADseq for 81 Stichodactyla haddoni and 99 Entacmaea quadricolor individuals to test for population genetic structure. We find evidence that both species predominantly propagate via sexual reproduction, and asexual reproduction is limited. We observe panmixia that indicates the absence of effective dispersal barriers for these species living in a highly anthropogenically disturbed environment. This is positive news for both species that are also found in the aquarium trade. More fundamentally, our results suggest that inhabiting different parts of a shallow reef may not affect a species’ population connectivity nor favour asexual reproduction.