Inhibition of pathogenic Vibrio harveyi using calamenene, derived from the Indian gorgonian Subergorgia reticulata, and its synthetic analog.

We report the synthesis and antimicrobial properties of a partially reduced dihydronathphthoquinone analogue of 2-methoxy, 5-acetoxy calamenene, extracted from Subergorgia reticulata. The growth of a pathogenic Vibrio harveyi strain was effectively controlled by the calamenene derivative 1 (Cala1) and its synthetic analog 2 (Cala2). Complete mortality of V. harveyi was observed with 2.5 and 0.5 µg mL-1 concentrations of Cala1 and Cala2, respectively. The metabolic assays demonstrated that Cala1 is a bacteriostatic agent while Cala2 showed bactericidal properties. It was confirmed that translocation of Cala2 into the cytoplasm does not induce any change to the integrity of the bacterial cell wall. The Cala2 induced damage to the genetic material of 70% of cells while genetic material of 91% of cells treated with Cala1 remained intact. The Cala2 is, therefore, proposed as a potential bactericidal compound against the aquaculture pathogen V. harveyi. The fact that the Cala2 exhibited minimal cytotoxicity to Artemia nauplii indicates its potential use as an antimicrobial agent for aquaculture operations.

Influence of environmental factors on macrofoulant assemblages on moored buoys in the eastern Arabian Sea.

Factors governing the distribution of organisms in the pelagic ocean are understudied. In this paper we describe environmental parameters and macrofouling assemblages on 11 buoys deployed in the Arabian Sea for an average duration of 322 days. Macrofoulants on all the mooring components extending from the sea-surface to a depth of 1800-4300 m were documented. Role of temperature, salinity, dissolved oxygen, biological productivity and zooplankton community in governing the macrofoulant distribution are described. Species composition, vertical zonation and wet biomass exhibited significant spatial variations. Lepas anatifera constituted more than 90% of foulant wet biomass on all moorings. Assemblages in the southeastern (SEAS), east-central (ECAS) and northeast (NEAS) regions were distinct. Density of L. anatifera on surface buoys were low in SEAS (0.2±0.09 no./cm2), high in ECAS (0.32±0.11 no./cm2) and moderate in NEAS (0.23±0.04no./cm2). Macrofoulants were observed up to a depth of 75 m in SEAS, 130 m in ECAS and 120 m in NEAS. The depth profile of macrofoulant assemblages on moorings could be related to the prevalent hypoxic condition. Vertical profiles of wet biomass on all moorings exhibited subsurface maxima at depth ranging from 10 to 20 m, consequent to the abundance of L. anatifera in a thermally stable depth of water column, wherein diurnal and semidiurnal temperature variability was minimal. We attribute the observed variation in fouling assemblages to dissolved oxygen levels, salinity and diurnal variability in temperature and salinity.

Sediment Oxygen Demand in Cochin backwaters, a tropical estuarine system in the south-west coast of India.

Eutrophication has often been one of the major problems encountered in estuaries and coastal waters. The oxic/anoxic status of an estuary can be effectively determined by measurement of the Sediment Oxygen Demand (SOD). The present study forms a pioneering attempt to evaluate the SOD of the Cochin Backwater System (CBS), a tropical eutrophic estuary in the south-west coast of India. The CBS exhibited significant spatio-temporal variations in SOD. The mean net SOD during the dry season (2569.73 µmol O(2) m(-2) h(-1)) was almost twice that of the wet season (1431.28 µmol O(2) m(-2) h(-1)), presumably due to higher discharge during the latter season. The observed pockets of net oxygen release indicate that the CBS still retains certain autotrophic regions in spite of heavy organic drains. The low oxygen flux in light chambers points towards the role of microphytobenthos in maintaining the oxygen reservoir of the estuarine system.

Calamenenes--aromatic bicyclic sesquiterpenes--from the Indian gorgonian Subergorgia reticulata (Ellis and Solander, 1786).

Three aromatic sesquiterpene derivatives, (+)-(7R, 10S)-2-methoxy calamenene (1), (+)-(7R, 10S)-2,5-dimethoxy calamenene (2) and (+)-(7R, 10S)-2-methoxy-5-acetoxy calamenene (3) were isolated from the methanol extract of the Indian gorgonian Subergorgia reticulata. Compound 2 has not been previously described in the literature. Compound 3 has not been isolated previously from a natural source. Compounds 1, 2 and 3 showed settlement inhibition activity against cyprids of Balanus amphitrite with EC(50) values of 4.4, 7.8 and 0.03 µg mL(-1), respectively. These compounds also exhibited considerable activity against Artemia nauplii at 50 µg mL(-1), indicative of their potential use as cytotoxic agents.