Antifouling activity of the methanolic extract of Syringodium isoetifolium, and its toxicity relative to tributyltin on the ovarian development of brown mussel Perna indica

Antifouling coating based on biopolymers (PCL/ PLA) and bioactive extract from the sea cucumber Stichopus herrmanni

An important challenge to decrease the toxic effects of the common biocides in marine environments and to achieve suitable ecofriendly natural antifouling coatings is to find effective natural antifoulants and efficient biodegradable coatings. In this study, antifouling activities of nine bioactive extracts (non-polar to polar) from different organs of the sea cucumber Stichopus herrmanni were tested against five bacterial strains, barnacle and brine shrimp larvae. The ethyl acetate extract of the body wall showed the highest in-vitro antifouling activity including high antibacterial and anti-barnacle activities and low toxicity against the brine shrimp as non-target organism. Based on these results, 10 phr of the ethyl acetate extract from S.herrmanni was added to different coatings consisting of polycaprolactone (PCL)/polylactic acid (PLA) blends containing various compositions of PLA (0, 10, and 20 wt.%). Polyvinyl chloride panels were coated with the prepared antifouling coatings and immersed in seawater for three months. Panel coated with PCL 80% /PLA 20% containing 10 phr of the antifoulant (panel-5), showed the highest resistance against fouling settlement with fouling coverage of 41.66% (P < 0.05). In addition, the lowest fouling weight was measured in panel-5 as well (81.00 ± 9.85 g) (P < 0.05). These findings indicate the antibacterial and antifouling potential of semi-polar bioactive extracts from the S. herrmanni body wall as natural antifoulants, as well as the enhanced antifouling performance of PCL/the natural antifoulant coatings by adding PLA.

Bioaccumulation of TBT and Its Cellular Toxic Effects on the Freshwater Prawn Macrobrachium rosenbergii

To test the toxic effects of tributyltin (TBT), Macrobrachium rosenbergii were exposed to three concentrations of TBT viz. 10 ng/L, 100 ng/L and 1000 ng/L for 90 days. The bioaccumulation of TBT level varied in hepatopancreas based upon dose dependent manner. Histopathological results revealed the reduction in basement membrane thickness, disruption of the hepatopancreatic tubules and abnormal lumen in hepatopancreas of TBT treated prawns. The ultrastructure of the control prawn showed normal architecture of cellular organelles with prominent nuclei in hepatocytes. On the other hand, many vacuoles, irregular arrangements of microvilli, swollen mitochondria, distorted rough endoplasmic reticulum cisternaes and abnormal nucleus were seen in the TBT treated group. Further, the biochemical and vitellogenin content were altered remarkably due to TBT exposure. It directly indicated that TBT had conspicuously inhibited the vitellogenesis. Therefore, it was inferred that the administration of TBT has considerably affected the hepatopancreatic functions in M. rosenbergii.

First study on lipid dynamics during the female reproductive cycle of Polybetes pythagoricus (Araneae: Sparassidae)

Spiders are valuable to humans, not only for their role in health but also as biologic pest controllers. In oviparous species, lipids are the main energy source for embryo development and the growth and survival of larvae. Using the spider Polybetes pythagoricus (Holmberg, 1875) as an experimental model, we studied the fluctuations in lipids and fatty acids occurring in tissues related to vitellogenesis. Different reproductive stages (previtellogenesis, early vitellogenesis, vitellogenesis, and postvitellogenesis) were determined histologically. Gonadosomatic and hepatosomatic indices were first used in spiders. The midgut diverticula proved to be the organ with the highest lipid concentration, with triacylglycerols as the major component. Phospholipids were the principal lipids transported. In vitellogenesis, a major accumulation of lipids occurred in the ovary, principally phosphatidylethanolamine (41%); it probably synthesized in the midgut diverticula before being released into the hemolymph for transport and accumulation in the ovary. Phosphatidylethanolamine is possibly involved in maintaining membrane fluidity and in the function of the electron transport chain. The principal fatty acids in the different organs were palmitic, stearic, oleic, and linoleic acids. During vitellogenesis, the ovaries become enriched in polyunsaturated fatty acids. The lipid patterns in the male midgut diverticula, muscle, and hemolymph were similar to those of the previtellogenic or postvitellogenic females.

Environmentally benign antifouling activity and toxic properties of bioactive metabolites from mangrove Excoecaria agallocha L

This study was aimed to investigate the antifouling (AF) potentials and toxic properties of methanol extract from leaves of mangrove Excoecaria agallocha. Antimicrofouling activity results inferred that this extract strongly inhibited fouling bacterial and microalgal growth. This extract had also inhibited the settlement of brown mussel Perna indica and larvae of barnacle Balanus amphitrite. Further, EC₅₀ < LC₅₀ and therapeutic ratio > 1 together propagated non-toxic nature of the extract. Mollusk foot adherence assay result showed complete inhibition of foot spreading and loss of attachment of common rocky fouler Patella vulgata to the substrata. Field assay results affirmed that this extract effectively deterred settlement of biofoulers. Purification and GC-MS analysis of bioassay-guided active spot evidenced presence of three major compounds (> 85%) responsible for the promising AF activity. The identified lead compounds subjected to an estimation (BIOWIN™) program developed by United States Environmental Protection Agency (USEPA) predicts that they are biodegradable in nature. Graphical abstract.

Review on Molecular Mechanisms of Antifouling Compounds: An Update since 2012

Better understanding of the mechanisms of antifouling compounds is recognized to be of high value in establishing sensitive biomarkers, allowing the targeted optimization of antifouling compounds and guaranteeing environmental safety. Despite vigorous efforts to find new antifouling compounds, information about the mechanisms of antifouling is still scarce. This review summarizes the progress into understanding the molecular mechanisms underlying antifouling activity since 2012. Non-toxic mechanisms aimed at specific targets, including inhibitors of transmembrane transport, quorum sensing inhibitors, neurotransmission blockers, adhesive production/release inhibitors and enzyme/protein inhibitors, are put forward for natural antifouling products or shelf-stable chemicals. Several molecular targets show good potential for use as biomarkers in future mechanistic screening, such as acetylcholine esterase for neurotransmission, phenoloxidase/tyrosinase for the formation of adhesive plaques, N-acyl homoserine lactone for quorum sensing and intracellular Ca²⁺ levels as second messenger. The studies on overall responses to challenges by antifoulants can be categorized as general targets, including protein expression/metabolic activity regulators, oxidative stress inducers, neurotransmission blockers, surface modifiers, biofilm inhibitors, adhesive production/release inhibitors and toxic killing. Given the current situation and the knowledge gaps regarding the development of alternative antifoulants, a basic workflow is proposed that covers the indispensable steps, including preliminary mechanism- or bioassay-guided screening, evaluation of environmental risks, field antifouling performance, clarification of antifouling mechanisms and the establishment of sensitive biomarkers, which are combined to construct a positive feedback loop.

Antifouling Activity of Lipidic Metabolites Derived from Padina tetrastromatica

An attempt has been made to identify the potential seaweed for antifouling property due to the growing need for environmentally safe antifouling systems. The antibacterial, antimicroalgal, and antimussel foot adherence potentials of methanol, dichloromethane, and hexane extracts of the chosen seaweeds such as Padina tetrastromatica, Caulerpa taxifolia, and Amphiroa fragilissima have been compared against copper sulfate. Among the extracts, the maximum antibacterial activities were exhibited by the methanol extract of P. tetrastromatica. The minimum inhibitory concentration (MIC) of the methanolic extract of P. tetrastromatica was found to be 10 and 1 μg/ml against test biofilm bacteria and diatoms, respectively. The antimussel foot adherence assay indicated that the extract had inhibited the foot adherence of the green mussels Perna viridis with the effective concentration (EC50) of 25.51 ± 0.03 μg/ml, and lethal concentration for 50 % mortality (LC50) was recorded at 280.22 ± 0.12 μg/ml. Based on the prolific results, the crude methanolic extract of P. tetrastromatica was subjected to purification using silica gel column and thin-layer chromatography (TLC). Then, the active compounds of the bioassay-guided fraction (F13) were identified using gas chromatography coupled with mass spectroscopy (GC-MS), and it was observed that fatty acids were the major components, which may be responsible for the antifouling properties.

TBT effects on the development of intersex (ovotestis) in female fresh water prawn Macrobrachium rosenbergii

The impact of tributyltin (TBT) on the female gonad and the endocrine system in Macrobrachium rosenbergii was studied. Prawns were exposed to environmentally realistic concentrations of 10, 100, and 1000 ng/L of TBT for 6 months. Dose dependent effects were noticed in TBT exposed prawns. At 1000 ng/L TBT caused ovotestis formation (formation of male germ cells in ovary). Presence immature oocytes, fusion of developing oocytes, increase in interstitial connective tissues, and its modification into tubular like structure and abundance of spermatogonia in the ovary of TBT treated prawns. The control prawn ovary showed normal architecture of cellular organelles such as mature oocytes with type 2 yolk globules, lipid droplets, normal appearance of yolk envelop, and uniformly arranged microvilli. On the other hand, type 1 yolk globules, reduced size of microvilli, spermatogonial cells in ovary, spermatogonia with centrally located nucleus, and chromatin distribution throughout the nucleoplasm were present in the TBT treated group. Immunofluorescence staining indicated a reduction in vitellin content in ovary of TBT treated prawn. Moreover, TBT had inhibited the vitellogenesis by causing hormonal imbalance in M. rosenbergii. Thus, the present investigation demonstrates that TBT substantially affects sexual differentiation and gonadal development in M. rosenbergii.

Antifouling and toxic properties of the bioactive metabolites from the seagrasses Syringodium isoetifolium and Cymodocea serrulata

The present study documents the antifouling and toxic properties of seagrasses Syringodium isoetifolium and Cymodocea serrulata. For that, the seagrasses S. isoetifolium and C. serrulata were extracted individually using organic solvents viz. dichloromethane, acetone and methanol. Amongst the extracts, the maximum antimicrofouling and antimacrofouling activities were exhibited by methanol extracts of both the seagrasses. The Minimal Inhibitory Concentration (MIC) of methanolic extracts of seagrasses was ranged from 1.0 to 10µg/ml against test biofilm bacteria and microalgal strains. Similarly, 100% fouling inhibition of limpet Patella vulgata was found at 6.0mg/ml of methanolic extracts of seagrasses. The mussel Perna indica showed 50% of byssal production and attachment inhibition at 21.51±2.03, 17.82±1.07µg/ml and the anticrustaecean activity for 50% mortality of Artemia salina was recorded at 732.14±9.21 and 394.16±5.16µg/ml respectively for methanolic extracts of S. isoetifolium and C. serrulata. The minimal inhibitory and higher lethal concentrations of active methanol extracts shows it׳s less toxic nature. Based on the prolific results, methanol extracts of S. isoetifolium and C. serrulata were subjected to purification using silica gel column and thin layer chromatography. Then the active compounds of the bioassay guided fractions were partially characterized using gas chromatography coupled with mass spectroscopy (GC-MS) and keyed out that fatty acids (C16 to C24) were the major components which responsible for the antifouling properties of the candidate seagrasses.