Antimicrobial profiling of coral reef and sponge associated bacteria from southeast coast of India

Culturable bacteria associated with marine sponges and coral mucus (collected from Gulf of Mannar and Palk Bay) were screened for their prospective antimicrobial compounds against 9 bacterial pathogens (Bacillus megaterium, B. cereus, Salmonella typhimurium, Staphylococcus aureus, Proteus vulgaris, Klebsillla pneumoniae, Escherichia coli, Pseudomonas aeruginosa and Acinetobacter baumannii) and a fungal pathogen (Candida albicans). Of the 263 bacterial isolates obtained during this study, 52 isolates displayed antimicrobial activity against one or more pathogens. 16S rRNA gene sequencing revealed that these 52 strains affiliated to 14 genera from three phyla Proteobacteria, Firmicutes and Actinobacteria. Sponge associated bacterial strains F-04, I-23, I-33 and G-03 inhibited the growth of all the bacterial pathogens tested in this study and significantly the former 2 strains inhibited the growth of fungal pathogen also. Majority of the potential strains (88.4% out of 52 strains) inhibited the growth of Bacillus cereus. Interestingly, an actinomycete strain F-04 (isolated from sponge Orina sagittaria) inhibited the growth of methicillin resistant Staphylococcus aureus. In total, 10 volatile organic compounds were determined from the ethyl acetate and hexane extract of the strain F-04 using GC-MS. Overall, marine bacteria isolated during this study demonstrate the potential for the development of broad spectrum antibiotics.

Improved Sprouting and Growth of Mung Plants in Chromate Contaminated Soils Treated with Marine Strains of Staphylococcus Species

Marine bacteria possess a wide variety of bioremediation potential which is beneficial environmentally and economically. In this study, bacterial isolates from marine waters were screened for tolerance and growth in high concentrations of chromate (Cr⁶⁺). Two isolates, capable of tolerating Cr⁶⁺ concentrations 300 µg mL^-1 or higher, and found to completely reduce 20 µg mL^-1 Cr⁶⁺ were grown in Cr⁶⁺ (50 and 100 mg kg^-1) spiked garden soil. Notably, both facilitated normal germination and growth of mung (Vigna radiata) seeds, which could hardly germinate in Cr⁶⁺ spiked garden soil without either of these bacteria. In fact, large percent of mung seeds failed to sprout in the Cr⁶⁺ spiked garden soil and could not grow any further. Apparently, chromate detoxification by marine bacterial isolates and the ability of mung plants to deal with the reduced form appear to work complementarily. This study provides an insight into marine bacterial abilities with respect to chromium and potential applications in promoting growth of leguminous plants-similar to mung in particular-in Cr⁶⁺ contaminated soil.

Phylogenetic analyses and nitrate-reducing activity of fungal cultures isolated from the permanent, oceanic oxygen minimum zone of the Arabian Sea

Reports on the active role of fungi as denitrifiers in terrestrial ecosystems have stimulated an interest in the study of the role of fungi in oxygen-deficient marine systems. In this study, the culturable diversity of fungi was investigated from 4 stations within the permanent, oceanic, oxygen minimum zone of the Arabian Sea. The isolated cultures grouped within the 2 major fungal phyla Ascomycota and Basidiomycota; diversity estimates in the stations sampled indicated that the diversity of the oxygen-depleted environments is less than that of mangrove regions and deep-sea habitats. Phylogenetic analyses of 18S rRNA sequences revealed a few divergent isolates that clustered with environmental sequences previously obtained by others. This is significant, as these isolates represent phylotypes that so far were known only from metagenomic studies and are of phylogenetic importance. Nitrate reduction activity, the first step in the denitrification process, was recorded for isolates under simulated anoxic, deep-sea conditions showing ecological significance of fungi in the oxygen-depleted habitats. This report increases our understanding of fungal diversity in unique, poorly studied habitats and underlines the importance of fungi in the oxygen-depleted environments.

Full-length cloning and phylogenetic analyses of translationally controlled tumour protein and ferritin genes from the Indian white prawn, Fenneropenaeus indicus (H. Milne Edwards)

Elucidation, through molecular analyses, of bacterial afflictions in commercially important aquaculture-reared shrimps is pivotal for the prevention and/or control of disease outbreaks. In this study, we examined the phylogenetic relatedness and compared the possible immune-related functional roles of both translationally controlled tumour protein (TCTP) and ferritin genes with previous studies. Both TCTP and ferritin genes were substantially upregulated in the Indian white prawn, Fenneropenaeus indicus (H. Milne Edwards), post-larvae following bath challenge with the virulent strain of bacteria, Vibrio harveyi D3. Full-length cloning of these genes by rapid amplification of complementary DNA ends -polymerase chain reaction (RACE-PCR) yielded 727-base pair (bp)-long TCTP and 1212-bp-long ferritin gene sequences. Their open reading frames (ORFs) were 507 and 510 bp, respectively. The TCTP-ORF coded for 168 amino acids with three substitutions at positions 37, 141, 155, and the ferritin ORF coded for 170 amino acids with no species-specific substitutions. Phylogenetic analysis suggested the closest relatedness of both TCTP and ferritin from F. indicus to Chinese white prawn, Fenneropenaeus chinensis (Osbeck). In addition to reporting the full-length sequences of these immune-relevant genes, this study highlighted their conserved natures, which perhaps make them important defence-related proteins in the innate immune system of F. indicus.

Mobilization of manganese by basalt associated Mn(II)-oxidizing bacteria from the Indian Ridge System

The Indian Ridge System basalt bearing Mn-oxide coatings had todorokite as the major and birnesite as the minor mineral. We posit that microorganisms associated with these basalts participate in the oxidation of Mn and contribute to mineral deposition. We also hypothesized that, the Mn-oxidizing microbes may respond reversibly to pulses of fresh organic carbon introduced into the water column by mobilizing the Mn in Mn-oxides. To test these two hypotheses, we enumerated the number of Mn-oxidizers and -reducers and carried out studies on the mobilization of Mn by microbial communities associated with basalt. In medium containing 100 μM Mn(2+), 10(3) colony forming units (CFU) were recovered with undetectable number of reducers on Mn-oxide amended medium, suggesting that the community was more oxidative. Experiments were then conducted with basalt fragments at 4±2 °C in the presence 'G(+)' and absence 'G(-)' of glucose (0.1%). Controls included set-ups, some of which were poisoned with 15 mM azide and the others of which were heat-killed. The mobilization of Mn in the presence of glucose was 1.76 μg g(-1) d(-1) and in the absence, it was 0.17 μg g(-1) d(-1) after 150 d. Mn mobilization with and without added glucose was 13 and 4 times greater than the corresponding azide treated controls. However, rates in 'G(+)' were 16 times and 'G(-)' 24 times more than the respective heat killed controls. The corresponding total counts in the presence of added glucose increased from 1.63×10(6) to 6.71×10(7) cells g(-1) and from 1.41×10(7) to 3.52×10(7) cells g(-1) in its absence. Thus, the addition of glucose as a proxy for organic carbon changed the community's response from Mn(II)-oxidizing to Mn(IV)-reducing activity. The results confirm the participation of Mn oxidizing bacteria in the mobilization of Mn. Identification of culturable bacteria by 16S rRNA gene analysis showed taxonomic affiliations to Bacillus, Exiguobacterium, Staphylococcus, Brevibacterium and Alcanivorax sp.

Attenuation of Pseudomonas aeruginosa virulence by marine invertebrate-derived Streptomyces sp

The study aimed to discover quorum sensing (QS) inhibitors from marine sponge-derived actinomycetes and analyse its inhibitory activities against QS-mediated virulence factors in Pseudomonas aeruginosa. Seventy-two actinomycetes isolated from marine invertebrates collected from the western coast of India were screened against the QS indicator strain Chromobacterium violaceum CV12472. Methanol extracts of 12 actinomycetes showing inhibition of violacein production were accessed for downregulation of QS-mediated virulence factors like swarming, biofilm formation, pyocyanin, rhamnolipid and LasA production in Ps. aeruginosa ATCC 27853. The isolates NIO 10068, NIO 10058 and NIO 10090 exhibited very good anti-QS activity, with NIO 10068 being the most promising one. Mass spectrometric analysis of NIO 10068 methanol extract revealed the presence of cinnamic acid and linear dipeptides proline-glycine and N-amido-α-proline in the active extract. Detailed investigation suggested that although linear dipeptide Pro-Gly is to some extent responsible for the observed biological activity, cinnamic acid seems to be the main compound responsible for it. Marine-derived actinomycetes are a potential storehouse for QS inhibitors.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report not only on marine sponge-associated Streptomyces for anti-QS in Ps. aeruginosa but also on cinnamic acid and proline-derived linear dipeptides proline-glycine as QS inhibitors. The results reveal that marine-derived actinomycetes may not only play a role in the defensive mechanism of their host but also lead to new molecules useful in the development of novel antivirulence drugs.

A role for antioxidants in acclimation of marine derived pathogenic fungus (NIOCC 1) to salt stress

Salinity tolerance a key factor helps in understanding the ionic homeostasis in general, which is a fundamental cellular phenomenon in all living cells. Here, a marine derived pathogenic fungus was examined for its adaptation under salt stress using antioxidant properties. The aqueous extracts of halophilic fungus exhibited different levels of antioxidant activity in all the in vitro tests such as α,α-diphenyl-β-picrylhydrazyl (DPPH(·)), Hydroxyl Radical Scavenging Assay (HRSA), Metal chelating assay and β-carotene-linoleic acid model system. The antioxidant capacity of marine fungus exposed to high salt condition showed an increase in activity. In addition, the production of intra and extracellular antioxidant enzymes of the fungus at various salt stresses were analyzed and discussed for their possible role in the stress mechanism. The marine derived fungus was identified as Phialosimplex genus, which is associated with infections in dogs. Thus the present study elucidates that the scavenging activity is one of the protective mechanisms developed in the fungus to avoid the deleterious effect of salt stress. In addition, the study also helps in understanding how the pathogenic fungus tackles the oxidative burst i.e. hypersensitivity reaction performed by host to kill the pathogens.

Distribution of butyltins in the waters and sediments along the coast of India

Water and surface sediment samples were analyzed for butyltins (TBT, DBT, MBT) from various ports along the east and west coast of India. The total butyltin (TB) in water samples varied between ~1.7 and 342 ng S nl⁻¹, whereas for sediments it varied between below detection limit to 14861 ng S ng⁻¹ dry weight of sediment. On an average Chennai port recorded the highest level of butyltins in the sediments while Paradip recorded the highest level of butylins in the waters. A fairly good relationship between the TB in the sediment and overlying water samples, as well as between organic carbon and TB, implicates the importance of adsorption/desorption process in controlling the levels of TBT in these port areas. In India the data on organotin pollution is very sparse; most of the port areas have been surveyed for butyltins for the first time during this study.

Distribution of butyltins in waters and sediments of the Mandovi and Zuari estuaries, west coast of India

Butyltins (TBT, DBT, MBT) were measured in water and sediment samples collected from various locations in the Mandovi (ten stations) and Zuari (nine stations) estuaries during November 2007. The total butyltin (TB) in water samples varied between approximately 12 and 73 and from 0.5 to 77 ng Sn l(-1), whereas for the sediments, it varied from approximately 15 to 118 and 6 to 119 ng Sn g(-1) dry weight for the Mandovi and the Zuari estuaries, respectively. The average TB concentration in the sediments from the Zuari estuary was higher as compared to the Mandovi estuary, whereas for the water samples, it was vice versa. For both the water and sediment samples, MBT was generally the most predominant butyltin in these two estuaries. This suggests that the butyltin contamination was not freshly derived. Fairly good relationships between the concentrations of TB and organic carbon in water and sediment samples of these estuaries implicate the importance of adsorption/desorption processes in controlling the levels of TB in these estuaries.

Seasonal variation in organotins in the waters of the Dona Paula Bay, west coast of India

Surface seawaters from the Dona Paula Bay, were collected at weekly intervals during March 2007 to March 2008, and analyzed for butyltins (BT) such as tributyltin (TBT), dibutyltin (DBT), monobutyltin (MBT) using a GC-MS system. The mean concentrations of TBT, DBT, MBT and total BT varied from <1-37, 4-19, 6-28 and 21-84 ng Sn L(-1), respectively. Highest levels of BTs were recorded during May followed by April 2007 and March 2007 probably because the shipping and tourism activities are very high during these months.