Marine macroalga-associated heterotrophic Bacillus velezensis: a novel antimicrobial agent with siderophore mode of action against drug-resistant nosocomial pathogens

Glutamicibacter sp. ZY1 antagonizes pathogenic Vibrio parahaemolyticus via iron competition

Probiotics are prior agents for treating bacterial infection with advantages of inhibiting pathogenic bacteria and improving immune responses of hosts, thus increasing the survival rate of cultured animals. In this study, one Vibrio parahaemolyticus YDE17 pathogenic to shrimp and its antagonist Glutamicibacter sp. ZY1 were screened, and ZY1 showed stable inhibitory effects on diverse Vibrio spp., especially V. parahaemolyticus. ZY1 secreted inhibitory substances into supernatant, and the activity of inhibitory substances did not change after being treated under different temperatures, proteinase K, and pH (6-10), which indicated that the inhibitory substances might be small molecules, which led us to trace the siderophore production. The siderophore production of YDE17 co-incubated with the cell-free supernatant of ZY1 was greater than that of YDE17 alone, which indicated that the cell-free supernatant of ZY1 created iron-limiting conditions for YDE17. This finding was confirmed by iron supplementation assays, in which the inhibitory activity of the cell-free supernatant of ZY1 on YDE17 as well as the siderophore production of YDE17 decreased in the presence of FeCl3. The effect of iron on inhibition was further confirmed by in vivo infection. The relative percent survival of ZY1 to shrimp challenged by YDE17 was 83.3%, but the survival rates of shrimp challenged with YDE17/ZY1/FeCl3 were similar to that of YDE17, both of which were significantly lower than the 70% survival rate of shrimps simultaneously challenged by ZY1/YDE17. Our study offers a new probiotic resource to control vibriosis, which works through iron competition with the opportunistic pathogens of Vibrio spp.IMPORTANCEBacteria belonging to Vibrio spp., especially Vibrio parahaemolyticus, are important opportunistic pathogens infecting a wide range of hosts including fish, shrimp, shellfish, and crab. Antibiotics are effective but show the disadvantages of antibiotic generation, microecology destruction, and biological toxicology; thus, new treatments of Vibrio infection are urgently recommended. In our present study, Glutamicibacter sp. ZY1, belonging to the phylum Actinomycetes, was selected and showed high inhibitory activity to inhibit V. parahaemolyticus pathogenic to shrimp. Glutamicibacter sp. ZY1 antagonized V. parahaemolyticus YDE17 through producing siderophore to compete for iron, based on the results of both in vitro and in vivo experiments under different iron levels. This study offers a new strategy to control Vibrio infection in aquaculture.

Antimicrobial Potential of Marine Sponge-Associated Bacillus velezensis and Stutzerimonas stutzeri from the Indian Coast: A Genome Mining and Metabolite Profiling Approach

Antimicrobial resistance (AMR) is one of the leading health crises worldwide that demands new antimicrobials to enter the clinical pipeline. Marine sponges are a rich source of promising bioactive compounds. Due to their sessile nature and filter-feeding lifestyle, sponges are prone to attack by competitors, predators, and pathogens. To combat these threats, they produce a diverse array of bioactive compounds. Notably, the microbial communities residing within the sponges make many of these beneficial compounds. Twenty-one bacterial isolates from various marine sponges from the Indian coast were selected for this study. The bacterial isolates were fermented to obtain crude extracts, which were then screened against critical bacterial pathogens. Based on the MIC (minimum inhibitory concentration) results, two isolates, Bacillus velezensis NIO_002 and Stutzerimonas stutzeri NIO_003 showing good activity, were characterized by morphological, biochemical, and molecular methods. Genome mining predicted multiple antibiotic biosynthetic gene clusters, most of which showed a high degree of similarity to known gene clusters, and some with low or no similarity which may be indicative of novel gene clusters. LC-MS (liquid chromatography-mass spectrometry) data revealed the putative presence of certain antibacterial compounds previously reported in the literature. To our knowledge, this is the first study to report the antimicrobial activity of marine sponge-associated Bacillus velezensis and Stutzerimonas stutzeri strains characterized by whole genome sequencing, thereby indicating the novelty of our strains. This study emphasizes the potential of our bacterial isolates for further development as a source of promising antibiotics to address the escalating challenge of drug-resistant pathogens.

β-(1 → 3) Linked Sulfated Polygalactan from a Seaweed-associated Bacillus velezensis MTCC 13097: A Potential Lead Against Human Hepatocellular Adenocarcinoma

Among tumors, liver cancer has an inferior prognosis. Therefore, exploring alternative strategies to improve the effectiveness of treatment for this ailment is of utmost urgency. In this study, we focused on analyzing the anti-cancer properties of bacterial exopolysaccharide from Bacillus velezensis associated with the seaweed Sargassum wightii against hepatocellular adenocarcinoma. A culture-dependent method was used to isolate heterotrophic B. velezensis, which was then evaluated for its antioxidant and anti-cancer properties. A β-(1 → 3) linked sulfated polygalactan exopolysaccharide (BVEP-2) was isolated from the bacterial extract and characterized by spectroscopic analysis. The anti-cancer property was analyzed through assays involving 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), neutral red uptake (NRU), and apoptosis (by annexin V-FITC/PI staining) against the human hepatocellular adenocarcinoma cell line (HepG2). BVEP-2 demonstrated potential cytotoxicity in the MTT assay (IC50 65.05 μg/mL) and 23.02% cell viability in the NRU assay at a 100 µg/mL concentration of BVEP-2 against HepG2, compared to the standard doxorubicin. Potential antioxidant properties of BVEP-2 (IC50 112-117 µg/mL) corroborated the anti-cancer activities, and the attenuation of free radicals could play a significant role in its anti-cancer potential. BVEP-2 induced approximately 9% early apoptosis and 39% late apoptosis in the HepG2 cell line, whereas the standard drug resulted in around 38% early apoptosis and 37% late apoptosis, along with 6% necrotic cells. The β-(1 → 3) linked sulfated polygalactan exopolysaccharide (BVEP-2) of B. velezensis MTCC13097 showed potential antioxidant and anti-cancer activities, and thus, could be developed as a promising pharmacophore lead against human hepatocellular adenocarcinoma.

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.

Pharmacological potential of seaweed-associated heterotrophic Firmicutes

Seaweed-associated bacterial symbionts are sources of potential pharmacological properties. The present study resulted in the culture-dependent isolation of bioactive heterotrophs belonging to the bacterial phylum Firmicutes, which were dominated more than 30% of the 127 cultivable isolates, among which 23 of them showed potential antimicrobial activities against a wide range of pathogens. The symbionts isolated from the seaweed Sargassum wightii showed significant bioactivity. Those were characterised as Bacillus safensis MTCC13040, B. valismortis MTCC13041, B. velezensis MTCC13044, B. methylotrophicus MTCC13042, Oceanobacillus profundus MTCC13045, B. tequilensis MTCC13043, and B. altitudinis MTCC13046. The organic extracts of the studied isolates showed potential antimicrobial properties against methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococci (minimum inhibitory concentration 6.25-12.5 μg ml^-1 ). The organic extract of B. altitudinis MTCC13046 displayed significantly greater radical quenching ability (IC₉₀ 133 μg ml^-1 , p < 0.05) other than attenuating hydroxymethyl glutaryl coenzyme A reductase (IC₉₀ 10.21 μg ml^-1 , p < 0.05) and angiotensin converting enzyme-1 (IC₉₀ 498 μg ml^-1 , p < 0.05) relative to other studied heterotrophs. The organic extract of B. tequilensis MTCC13043 displayed significantly greater attenuation potential against pro-inflammatory 5-lipooxygenase (IC₉₀ 5.94 μg ml^-1 , p < 0.05) and dipeptidyl peptidase-4 (IC₉₀ 271 μg ml^-1 , p < 0.05). The seaweed-associated B. altitudinis MTCC13046 and B. tequilensis MTCC13043 could be used to develop promising pharmacological leads.

Seaweed-associated heterotrophic bacteria: are they future novel sources of antimicrobial agents against drug-resistant pathogens?

Emergence of multidrug-resistant microorganisms and requirements for novel antimicrobial compounds necessitate exploring newer habitats to develop potential bioactive leads. Culture-contingent analysis of heterotrophic bacterial flora from the seaweeds led to the isolation of bioactive strains possessing potential antibacterial properties against wide-ranging clinical pathogens viz., methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus faecalis (VREfs). Seven of the most active strains belonging to the phylum Firmicutes isolated from a brown seaweed (Phaeophyceae) Sargassum wightii exhibited spot-over-lawn assay guided inhibition zone of larger than 30 mm. Integrated phenotypic and genotypic studies have led to the characterization of the seaweed-associated bacteria particularly belonging to the phylum Firmicutes. The organic extracts of the studied bacteria exhibited promising antibacterial properties against MRSA and VREfs with minimum inhibitory concentration ranging between 6.25 and 12.50 μg/mL. Time-kill kinetic profiles of those bacteria displayed rapid bactericidal activity against both E. coli and MRSA, showing a ≥ 3log₁₀ reduction in viable cell count than the initial. Among the studied bioactive Bacillus spp, B. tequilensis MTCC13043 and B. altiitudinis MTCC13046 were found to possess functional polyketide synthase (pks) gene (MW027664 and MW027660) that could be amplified. The outcome of amplified genes encrypting for polyketide synthase in conjunction with antibacterial activities unveiled the broad-spectrum antimicrobial activities of the marine heterotrophic Firmicutes, which could be further used against the emergent problem of antibiotic-resistant bacterial pathogens.

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.