An Analysis of Biosynthesis Gene Clusters and Bioactivity of Marine Bacterial Symbionts

Chengkuizengella axinellae sp. nov., a symbiotic bacterium isolated from a marine sponge of the genus Axinella

A Gram-stain-positive, strictly aerobic, creamy-white colored, endospore-forming and non-motile rods strain, designated as strain 2205SS18-9T, was isolated from a marine sponge, Axinella sp. collected from Seopseom Island, Republic of Korea. Optimal growth of strain 2205SS18-9T was observed at 25-30 °C, pH 6.5-7.0, and in the presence of 3.0% (w/v) NaCl. Cells were oxidase-positive and catalase-negative. Negative for nitrate reduction and indole production. Phylogenetic analyses based on the 16S rRNA gene and whole-genome sequences revealed that strain 2205SS18-9T formed a distinct phyletic lineage in the genus Chengkuizengella, and it was most closely related to Chengkuizengella marina YPA3-1-1T and Chengkuizengella sediminis J15A17T with 97.1 and 96.6% 16S rRNA gene sequence similarities, respectively. The average nucleotide identity and digital DNA-DNA hybridization values between strain 2205SS18-9T and Chengkuizengella marina YPA3-1-1T were 79.0 and 21.6%, respectively. The genomic DNA G + C content was 34.1%. The genome harbors a number of host-adhesion and transporter genes, suggested that strain 2205SS18-9T may interact with its sponge host as a symbiont. Menaquinone-7 was the sole isoprenoid quinone and antieiso-C15:0 (28.5%), iso-C16:0 (25.8%), C16:1 ω7c alcohol (15.0%), and iso-C15:0 (11.2%) were detected as the major fatty acids. Polar lipids included diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, two unidentified aminophospholipids, and an unidentified lipid. The cell-wall peptidoglycan contained lysine, alanine, glutamate, and aspartate. Based on these analyses, strain 2205SS18-9T represents a novel species of the genus Chengkuizengella, for which the name Chengkuizengella axinellae sp. nov. is proposed. The type strain is 2205SS18-9T (= KACC 23238T = LMG 33063T).

Diversity and Functionality of Bacteria Associated with Different Tissues of Spider Heteropoda venatoria Revealed through Integration of High-Throughput Sequencing and Culturomics Approaches

Spiders host a diverse range of bacteria in their guts and other tissues, which have been found to play a significant role in their fitness. This study aimed to investigate the community diversity and functional characteristics of spider-associated bacteria in four tissues of Heteropoda venatoria using HTS of the 16S rRNA gene and culturomics technologies, as well as the functional verification of the isolated strains. The results of HTS showed that the spider-associated bacteria in different tissues belonged to 34 phyla, 72 classes, 170 orders, 277 families, and 458 genera. Bacillus was found to be the most abundant bacteria in the venom gland, silk gland, and ovary, while Stenotrophomonas, Acinetobacter, and Sphingomonas were dominant in the gut microbiota. Based on the amplicon sequencing results, 21 distinct cultivation conditions were developed using culturomics to isolate bacteria from the ovary, gut, venom gland, and silk gland. A total of 119 bacterial strains, representing 4 phyla and 25 genera, with Bacillus and Serratia as the dominant genera, were isolated. Five strains exhibited high efficiency in degrading pesticides in the in vitro experiments. Out of the 119 isolates, 28 exhibited antibacterial activity against at least one of the tested bacterial strains, including the pathogenic bacteria Staphylococcus aureus, Acinetobacter baumanii, and Enterococcus faecalis. The study also identified three strains, GL312, PL211, and PL316, which exhibited significant cytotoxicity against MGC-803. The crude extract from the fermentation broth of strain PL316 was found to effectively induce apoptosis in MGC-803 cells. Overall, this study offers a comprehensive understanding of the bacterial community structure associated with H. venatoria. It also provides valuable insights into discovering novel antitumor natural products for gastric cancer and xenobiotic-degrading bacteria of spiders.

Natural Products and Pharmacological Properties of Symbiotic Bacillota (Firmicutes) of Marine Macroalgae

The shift from the terrestrial to the marine environment to discover natural products has given rise to novel bioactive compounds, some of which have been approved for human medicine. However, the ocean, which makes up nearly three-quarters of the Earth's surface, contains macro- and microorganisms whose natural products are yet to be explored. Among these underexplored marine organisms are macroalgae and their symbiotic microbes, such as Bacillota, a phylum of mostly Gram-positive bacteria previously known as Firmicutes. Macroalgae-associated Bacillota often produce chemical compounds that protect them and their hosts from competitive and harmful rivals. Here, we summarised the natural products made by macroalgae-associated Bacillota and their pharmacological properties. We discovered that these Bacillota are efficient producers of novel biologically active molecules. However, only a few macroalgae had been investigated for chemical constituents of their Bacillota: nine brown, five red and one green algae. Thus, Bacillota, especially from the marine habitat, should be investigated for potential pharmaceutical leads. Moreover, additional diverse biological assays for the isolated molecules of macroalgae Bacillota should be implemented to expand their bioactivity profiles, as only antibacterial properties were tested for most compounds.

Marine Bacterial Secondary Metabolites: A Treasure House for Structurally Unique and Effective Antimicrobial Compounds

The prevalence of antimicrobial resistance reduces the effectiveness of antimicrobial drugs in preventing and treating infectious diseases caused by pathogenic organisms, such as bacteria, fungi, and viruses. Because of the burgeoning growth of microbes with antimicrobial-resistant traits, there is a dire need to identify and develop novel and effective antimicrobial agents to treat infections from antimicrobial-resistant strains. The marine environment is rich in ecological biodiversity and can be regarded as an untapped resource for prospecting novel bioactive compounds. Therefore, exploring the marine environment for antimicrobial agents plays a significant role in drug development and biomedical research. Several earlier scientific investigations have proven that bacterial diversity in the marine environment represents an emerging source of structurally unique and novel antimicrobial agents. There are several reports on marine bacterial secondary metabolites, and many are pharmacologically significant and have enormous promise for developing effective antimicrobial drugs to combat microbial infections in drug-resistant pathogens. In this review, we attempt to summarize published articles from the last twenty-five years (1996–2020) on antimicrobial secondary metabolites from marine bacteria evolved in marine environments, such as marine sediment, water, fauna, and flora.