Biocontrol of Toxin Producing Cyanobacterium Microcystis aeruginosa by Algicidal Bacterium Exiguobacterium acetylicum Strain TM2 Isolated from Mid-Altitudinal Himalayan Lake of Northern India

Microcystis aeruginosa is a hepatotoxin producing cyanobacteria, found globally in freshwaters. In the present study, an algicidal bacterium against M. aeruginosa was isolated from Bhimtal Lake (29°20’39”N; 79°33’32”E) of Himalayan region of Uttarakhand, India. The isolated bacterium Exiguobacterium acetylicum strainTM2was identified by morphological characteristics, biochemical characteristics and partial 16S ribosomal DNA (rDNA) gene amplification (GenBank accession number: KX155561). Efficacy of E. acetylicum TM2, and its mode of algicidal activity was evaluated against M. aeruginosa. E. acetylicum TM2 showed intense anti-cyanobacterial effect against M. aeruginosa, and approximately 90.0 % death of M. aeruginosa cells were observed after 10 days of incubation. The bacterium attacked the M. aeruginosa cells directly by physically coming in contact and caused damaged to its membrane and internal organelles. Cell free filtrate of E. acetylicum TM2 did not exhibited algicidal activity, which indicates that mode of algicidal mechanism, is cell to cell contact, and not chemically mediated damage by algicidal compounds released from E. acetylicum TM2. Furthermore, in vitro and in vivo pathogenicity test confirm the non-virulence of E. acetylicum TM2 and so it could be potentially useful in mitigation of M. aeruginosa blooms in water.

Elucidation of the Algicidal Mechanism of the Marine Bacterium Pseudoruegeria sp. M32A2M Against the Harmful Alga Alexandrium catenella Based on Time-Course Transcriptome Analysis

The marine dinoflagellate Alexandrium is associated with harmful algal blooms (HABs) worldwide, causing paralytic shellfish poisoning (PSP) in humans. We found that the marine bacterium Pseudoruegeria sp. M32A2M exhibits algicidal activity against Alexandrium catenella (Group I), inhibiting its motility and consequently inducing cell disruption after 24 h of co-culture. To understand the communication between the two organisms, we investigated the time-course cellular responses through genome-wide transcriptome analysis. Functional analysis of differentially expressed genes revealed that the core reactions of the photosystem in A. catenella were inhibited within 2 h, eventually downregulating the entire pathways of oxidative phosphorylation and carbon fixation, as well as associated metabolic pathways. Conversely, Pseudoruegeria upregulated its glycolysis, tricarboxylic acid cycle, and oxidative phosphorylation pathways. Also, the transporters for nutrients such as C3/C4 carbohydrates and peptides were highly upregulated, leading to the speculation that nutrients released by disrupted A. catenella cells affect the central metabolism of Pseudoruegeria. In addition, we analyzed the secondary metabolite-synthesizing clusters of Pseudoruegeria that were upregulated by co-culture, suggesting their potential roles in algicidal activity. Our time-course transcriptome analysis elucidates how A. catenella is affected by algicidal bacteria and how these bacteria obtain functional benefits through metabolic pathways.

Loading Effects of Aminoclays in Co-Culture of Two Cyanobacterial Microcystis and Anabaena Species as an Algicidal Role

In recent decades, harmful algal blooms (HABs) have been significantly affecting environments, aquatic ecosystems, and human health, as well as damaging economies, especially near rivers and lakes, and in coastal regions. Microcystis and Anabaena are two genera of harmful cyanobacteria that will often predominate during toxic microalgal blooms. In this study, we employ a method for control and mitigation of HABs by microalgal cell instability using different types of aminoclays (ACs). Allelopathic interactions between the two strains of algae are studied in mono-culture, co-culture, and filtrated cell-free medium in the presence of the ACs. The growth of the Anabaena strain is significantly reduced by the cyanobacterial strains in the co-culture media, and both are significantly affected by the Acs’-enhanced algicidal activity. Anabaena sp. KVSF7 shows higher sensitivity against the ACs than does Microcystis sp. KW. In this way, the algicidal activity of ACs is harnessed, the effects of which are in the order of aluminum aminoclay (AlAC) > magnesium aminoclay (MgAC) > calcium aminoclay (CaAC). The ammonium sites in the ACs carry positive charges to induce instability of HABs along with the electrostatic attraction between algal cells and AC. Therefore, the utilization of the algicidal activity of the ACs can effectively reduce HABs, especially on cyanobacterial blooms.

Bioactivity of allelochemicals isolated from the roots of Echinacea purpurea L. Moench on Amaranthus viridis L., Portulaca oleracea L. and Microcystis aeruginosa

Based on the bioassay-guided strategy, we isolated 6-six allelochemicals [cichoric acid (I), 1,3-dicaffeoylquinic acid (II), 4,5-dicaffeoylquinic acid (III), chlorogenic acid (IV), 1-hydroxy-2-phthoic acid (V), echinacoside (VI)] from the roots of Echinacea purpurea (L.) Moench. Their structures were identified by nuclear magnetic resonance (NMR) and electrospray ionization mass spectrometry (ESI-MS) spectroscopic data. The bioassays studies included allelopathic and algicidal activities to test the effects of extracts and isolated fractions against the test weeds (Amaranthus viridis L., Portulaca oleracea L. and Microcystis aeruginosa Kutzing). At 100 µg/mL, compound (II) inhibited the shoot length and germination of A. viridis and P. oleracea weeds with the germination RI of -0.95±0.04 and -0.95±0.02, respectively. Furthermore, compound (III) showed the strongest inhibition of root length of P. oleracea L. We also found that compounds I-VI have algicidal activity. The compound (I) at low inoculum (5.0×102 cells mL-1) and high inoculum (1.0×104 cells mL-1), showed the highest algicidal activity of 78 % and 87.67 % 6 h after the treatment at 5 µg mL-1 respectively.

In vitro algicidal effect of polypyrrole on Prototheca species isolates from bovine mastitisAlgicidal activity of polypyrrole on Prototheca spp.

Algae of the genus Prototheca are microorganisms involved in the occurrence of diseases in humans and animals. In bovine species, Prototheca spp. cause environmental mastitis, productive losses in dairy herds, mainly leading to the discard of infected cows. Currently, there are no effective anti-Prototheca spp. drugs to combat this infection. Thus, the search for an efficacious therapy for Prototheca spp. infections have become essential. Highly soluble polypyrrole (Ppy) is a molecule with known antimicrobial activity. This study aimed to characterize Prototheca spp. isolates from bovine mastitis as well as to evaluate the susceptibility profile and to verify the morphological alterations on Prototheca spp. isolates treated with Ppy. In this research, 36 Brazilian isolates of Prototheca spp. were characterized by restriction fragment length polymorphism polymerase chain reaction (RFLP-PCR) assay for the mitochondrial cytB gene. Additionally, Ppy algicidal activity against these isolates of Prototheca spp. was assessed by minimal microbicidal concentration method in microplates. Further, scanning electron microscopy (SEM) was performed in order to verify the morphological alterations on Prototheca spp. isolates in response to Ppy. The isolates were characterized as belonging to Prototheca zopfii genotype 2 (35/36) and Prototheca blaschkeae (1/36). Ppy had an algicidal effect on all isolates tested at concentrations ranging from 15.625 μg ml−1 to 62.5 μg ml−1. SEM showed changes on planktonic and sessile P. zopfii, including a decrease of the number of cells with the presence of an amorphous substance involving the cells. The algicidal activity of Ppy suggests the therapeutic potential of this molecule in the prevention and treatment of Prototheca spp. in bovine mastitis.

Draft Genome Sequence of Pseudoalteromonas sp. Strain A25, a Bacterium with Algicidal Activity against Diatoms

Pseudoalteromonas sp. strain A25 is a marine bacterium that reveals strong algicidal activity against diatoms. We report the draft genome sequence for this strain, which consists of two contigs (3,887,303 bp and 850,536 bp). Further genomic analysis might facilitate an understanding of the algicidal mechanisms of this strain.