Comparative assessment of bacterial diversity associated with co-occurring eukaryotic hosts of Palk Bay origin.

Epibacterial communities of co-occurring eukaryotic hosts of Palk Bay origin (five seaweed species (Gracilaria sp, Padina sp, Enteromorpha sp, Sargassum sp, and Turbinaria sp) and one seagrass [Cymodaceae sp]) were analyzed for diversity and compared using 16S rRNA based Denaturant Gradient Gel Electrophoresis analysis. Diversity index revealed that Turbinaria sp hosts highest bacterial diversity while it was least in Gracilaria sp. The DGGE band profile showed that the epibacterial community differed considerably among the studied species. Statistical assessment using cluster analysis and Non-metric multidimensional scale analysis also authenticated the observed variability. Despite huge overlap, the composition of bacterial community structure differed significantly among the three closely related species namely Sargassum, Turbinaria and Padina. In addition, Enteromorpha and Sargassum, one being chlorophyta and the other phaeophyta showed about 80% similarity in bacterial composition. This differs from the general notion that epibacterial community composition will vary widely depending on the host phyla. The results extended the phenomenon of host specific epibacterial community irrespective of phylogeny and similarity in geographical location.

Epiphytic marine pigmented bacteria: A prospective source of natural antioxidants

Awareness on antioxidants and its significance in human healthcare has increased many folds in recent time. Increased demand requisite on welcoming newer and alternative resources for natural antioxidants. Seaweed associated pigmented bacteria screened for its antioxidant potentials reveals 55.5% of the organisms were able to synthesize antioxidant compounds. DPPH assay showed 20% of the organisms to reach a antioxidant zone of 1 cm and 8.3% of the strains more than 3 cm. Pseudomonas koreensis (JX915782) a Sargassum associated yellowish brown pigmented bacteria have better activity than known commercial antioxidant butylated hydroxytoluene (BHT) against DPPH scavenging. Serratia rubidaea (JX915783), an associate of Ulva sp. and Pseudomonas argentinensis (JX915781) an epiphyte of Chaetomorpha media, were also contributed significantly towards ABTS (7.2% ± 0.03 to 15.2 ± 0.09%; 1.8% ± 0.01 to 15.7 ± 0.22%) and FRAP (1.81 ± 0.01 to 9.35 ± 0.98; 7.97 ± 0.12 to 18.70 ± 1.84 μg/mL of AsA Eq.) respectively. 16S rRNA gene sequence analysis revealed bacteria that have higher antioxidant activity belongs to a bacterial class Gammaproteobacteria. Statistical analysis of phenolic contents in relation with other parameters like DPPH, ABTS, reducing power and FRAP are well correlated (p < 0.05). Results obtained from the current study inferred that the seaweed associated pigmented bacteria have enormous potential on antioxidant compounds and need to be extracted in a larger way for clinical applications.

Antimicrobial Activity of Bacteria Associated with Seaweeds against Plant Pathogens on Par with Bacteria Found in Seawater and Sediments.

Aim: We report antimicrobial activities of bacteria associated with 10 native and one invasive species of seaweeds on par with bacteria found in the seawater and sediment. Bacteria exhibiting antimicrobial activity were phylogenetically analysed using 16S rRNA gene. Place and Duration of Study: Samples of seaweeds, seawater and sediments collected at 6 localities of south east coast of India between December 2009 and January 2010 during monsoon season. Methodology: Culturable bacteria in seaweeds (epibiotics and endobiotics), seawater and sediments were isolated through serial dilutions using 1.5% ZoBell marine agar (HiMedia, India). Bacterial isolates producing antibiotics were identified by screening against commercial antibiotics and they were subjected to morphological, Gram’s staining and biochemical studies. Chemical property and stability of antimicrobial substances obtained from the promising bacteria active against plant pathogens were studied. Phylogenetic analysis of antibiotics-producing marine bacteria was made using 16S rRNA gene sequencing technique. Results: A number of673 isolates obtained through the isolation process were found to be the member of 27 bacterial genera, with species of Bacillus recording a maximum of 40.2%. Generally species of bacterial isolates in the association (seaweeds: epibiotics, 39.54% and endobiotics, 40.74%, seawater 8.61% and sediments 11.11%) produced antibiotics and active against plant pathogens (Xanthomonas axonopodis pv. citri, X. oryzaepv. oryzae and Ustilaginoidea virens) were associated with seaweeds (epibiotics 33.46% and endobiotics 43.11%) and sediments (23.43%). Extracellular components of active bacteria are proteins and retaining bioactivity at pH 7.0, up to 40°C and antifungal property up to 60°C. Extracts obtained from the active bacteria are nonpolar lipophilic substances exhibited only antifungal activity. Conclusion: Bacterial population were considerably higher in seaweeds as compared to seawater and sediments, and at the same time higher bacterial population was recorded in Gulf samples than the open coast samples. Most of the bacterial isolates associated with seaweeds were found to produce antibiotics.

Inhibition of attachment of some fouling diatoms and settlement of Ulva lactuca zoospores by film-forming bacterium and their extracellular products isolated from biofouled substrata in Northern Chile

The biofouling of surfaces submerged in the marine environment includes primary colonization of the substrate by microorganisms including bacteria, microalgae, and microscopic reproductive propagules of macroorganisms such as algal zoospores. The present study reports the evaluation of the inhibitory potential of biofilms and extracellular products (EP) of the indigenous bacterium Alteromonas sp strain Ni1-LEM on the settlement of marine biofouling such as: (i) eight marine benthic diatoms and (ii) zoospores of the alga Ulva lactuca, as well as the germination of these zoospores and was compared with reference strains with proven antifouling properties, Halomonas marina (ATCC 25374) and Pseudoalteromonas tunicata. Highest antifouling activity was found for the indigenous strain. In attempts to better define the chemical nature of the antifouling substance in the EP of the Alteromonas sp strain Ni1-LEM, the culture filtrates were tested for activity after heat treatment, enzymatic treatments, dialysis through semipermeable membranes, and separation into polar (aqueous) and non-polar (organic) fractions. The results suggested that the antifouling substance in the culture filtrates to be protein or peptide in nature, thermostable, hydrophilic, and equal to or greater than 3500 daltons in molecular size. Antifouling substances from bacteria may lead to the development of novel antifouling agents in the future.