Marine macroalga-associated heterotroph Bacillus velezensis as prospective therapeutic agent

A pan-genomic assessment: Delving into the genome of the marine epiphyte Bacillus altitudinis strain 19_A and other very close Bacillus strains from multiple environments

Marine macroalgae are the habitat of epiphytic bacteria and provide several conditions for a beneficial biological interaction to thrive. Although Bacillus is one of the most abundant epiphytic genera, genomic information on marine macroalgae-associated Bacillus species remains scarce. In this study, we further investigated our previously published genome of the epiphytic strain Bacillus altitudinis 19_A to find features that could be translated to potential metabolites produced by this microorganism, as well as genes that play a role in its interaction with its macroalgal host. To achieve this goal, we performed a pan-genome analysis of Bacillus sp. and a codon bias assessment, including the genome of the strain Bacillus altitudinis 19_A and 29 complete genome sequences of closely related Bacillus strains isolated from soil, marine environments, plants, extreme environments, air, and food. This genomic analysis revealed that Bacillus altitudinis 19_A possessed unique genes encoding proteins involved in horizontal gene transfer, DNA repair, transcriptional regulation, and bacteriocin biosynthesis. In this comparative analysis, codon bias was not associated with the habitat of the strains studied. Some accessory genes were identified in the Bacillus altitudinis 19_A genome that could be related to its epiphytic lifestyle, as well as gene clusters for the biosynthesis of a sporulation-killing factor and a bacteriocin, showing their potential as a source of antimicrobial peptides. Our results provide a comprehensive view of the Bacillus altitudinis 19_A genome to understand its adaptation to the marine environment and its potential as a producer of bioactive compounds.

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.

Seaweed-associated heterotrophic Bacillus altitudinis MTCC13046: a promising marine bacterium for use against human hepatocellular adenocarcinoma

Since the report of the antibiotic with anticancer properties, scientists have been focusing to isolate and characterize novel anti-microbial natural products possessing anticancer activities. The current study describes the production of seaweed-associated heterotrophic Bacillus altitudinis MTCC13046 with potential anticancer properties. The bacterium was screened for its capacity to diminish the cell proliferation of the human hepatocellular adenocarcinoma (HepG2) cell line, without upsetting the normal cells. The bacterial extract showed anticancer properties in a dose-reactive form against HepG2 (IC₅₀, half maximal inhibitory concentration ~ 29.5 µg/ml) on tetrazolium bromide analysis with less significant cytotoxicity on common fibroblast (HDF) cells (IC₅₀ ~ 77 µg/ml). The potential antioxidant ability of the organic extract of B. altitudinis MTCC13046 (IC₉₀ 133 µg/ml) could corroborate its capacity to attenuate the pathophysiology leading to carcinogenesis. The results of the apoptosis assay showed that the crude extracts of B. altitudinis maintained 68% viability in normal cells compared to 11% in the cancer cells (IC₅₀ 76.9 µg/ml). According to the findings, B. altitudinis MTCC13046 could be used to develop prospective anticancer agents.

Antimicrobial Biosynthetic Potential and Phylogenetic Analysis of Culturable Bacteria Associated with the Sponge Ophlitaspongia sp. from the Yellow Sea, China

Sponge-derived bacteria are considered to be a promising source of novel drugs, owing to their abundant secondary metabolites that have diverse biological activities. In this study, we explored the antimicrobial biosynthetic potential and phylogenetics of culturable bacteria associated with the sponge Ophlitaspongia sp. from the Yellow Sea, China. Using culture-dependent methods, we obtained 151 bacterial strains, which were then analysed for their antimicrobial activities against seven indicator strains. The results indicate that 94 (62.3%) of the 151 isolated strains exhibited antimicrobial activities and inhibited at least one of the indicator strains. Fifty-two strains were selected for further phylogenetic analysis using 16S rRNA gene sequencing, as well as for the presence of polyketide synthase (PKS) and non-ribosomal peptide synthetase (NRPS) genes. These 52 strains belonged to 20 genera from 18 families in 4 phyla, including Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria. Five strains with PKS genes and ten strains with NRPS genes were detected. Among them, two strains contained both PKS and NRPS genes. Notoacmeibacter sp. strain HMA008 (class Alphaproteobacteria) exhibited potent antimicrobial activity; thus, whole genome sequencing methods were used to analyse its secondary metabolite biosynthetic gene clusters. The genome of HMA008 contained 12 biosynthetic gene clusters that potentially encode secondary metabolites belonging to compound classes such as non-ribosomal peptides, prodigiosin, terpene, β-lactones, and siderophore, among others. This study indicates that the sponge Ophlitaspongia sp. harbours diverse bacterial strains with antimicrobial properties and may serve as a potential source of bioactive compounds.

Antibiotic-active heterotrophic Firmicutes sheltered in seaweeds: can they add new dimensions to future antimicrobial agents?

Appearance of drug-resistant microorganisms prompted researchers to unravel new environments for development of novel antimicrobial agents. Culture-supported analysis of heterotrophic bacteria associated with seaweeds yielded 152 strains, in that larger share of the isolates was embodied by Bacillus atrophaeus SHB2097 (54%), B. velezensis SHB2098 (24%), B. subtilis SHB2099 (12%), and B. amyloliquefaciens SHB20910 (10%). One of the most active strains characterized as B. atrophaeus SHB2097 (MW821482) with an inhibition zone more than 30 mm on spot-over-lawn experiment, was isolated from a seaweed Sargassum wightii, was selected for bioprospecting studies. Significant antibacterial potential was displayed by bacterial organic extract against vancomycin-resistant Enterococcus faecalis, Pseudomonas aeruginosa, methicillin-resistant Staphylococcus aureus, and Klebsiella pneumonia with minimum inhibitory concentration 6.25 µg/mL and comparable to the antibiotics ampicillin and chloramphenicol. The genes of type 1 pks (MZ222383, 700 bp) and hybrid nrps/pks (MZ222389, 1000-1400 bp) of B. atrophaeus MW821482 could be amplified. The bacterium displayed susceptibility to the commercially available antibiotic agents, and was negative for the pore-forming non-hemolytic hemolysin BL (hbl) and enterotoxin (nhe) genes, and therefore, was not pathogenic. The bacterium was found to possess genes (1000-1400 bp) involved in the biosynthesis of siderophore-class of compounds (MZ222387 and MZ222388) that showed 99% of similarity in BLAST search, and showed production of siderophore. Noteworthy antibacterial activities against clinically important pathogenic bacteria in conjunction with occurrence of genes coding for antimicrobial metabolites inferred that the marine heterotrophic bacterium B. atrophaeus SHB2097 could be used for the development of antibacterial agents against the emerging antibiotic resistance.

Bio-prospecting the future in perspective of amidohydrolase L-glutaminase from marine habitats

In the current scenario, considerable attention is being given to the enzyme L-glutaminase (EC 3.5.1.2). It belongs to the amidohydrolase class adherent to the family of serine-reliant β-lactamases and the penicillin-binding proteins due to its higher affinity to polymerize and modify peptidoglycan synthesis. However, based on the catalytic proficiency, L-glutaminase is characterized as a proteolytic endopeptidase that cleaves peptide linkage and emancipates various byproducts, viz. ammonia along with glutamate. L-glutamine is considered the key amino acid reportedly involved in multiple metabolic pathways such as nitrogen metabolism. The present review is focused on the recent development and aspects concomitant to the biotechnological applicability of L-glutaminase predominantly from the marine habitat. Additionally, a majority of L-glutaminases finds application in cancer therapy as therapeutic agents, especially for acute lymphocytic leukaemia. The in vitro studies have been effective against various human cancer cell lines. L-glutaminase enhances the growth of probiotic bacteria. Apart from all these applications, it is suitably applicable in fermented foods as a flavour enhancer especially the umami flavour and content. Marine habitats have largely been exploited for their bio-catalytic potential but very scarcely for therapeutic enzymes. Some of the reports of such marine bacterial isolates from Bacillus sp., Pseudomonas sp. and Vibrio sp. are in the domain, but none highlights the therapeutic applications predominantly as anticancer and anti-proliferative agents. KEY POINTS: The exploration of marine habitats along the Gujarat coasts mainly for bacteria secreting L-glutaminase is scarcely reported, and even more scarce are the amidohydrolases from these marine niches as compared to their terrestrial counterparts. Microbial sourced amidohydrolase has wide bio-applicability that includes food, cosmetics and therapeutics especially as anticancer/anti-proliferative agent making it of immense biotechnological significance.