Melanin is a photo-protective polymer found in many organisms. Our research shows that the bacteria associated with darkly pigmented sponges (Haliclona pigmentifera, Sigmadocia pumila, Fasciospongia cavernosa, Spongia officinalis, and Callyspongia diffusa) secrete non-cytotoxic melanin, with antioxidant activity that protects animal cells from photo-toxicity. Out of 156 bacterial strains screened, 22 produced melanin and these melanin-producing bacteria (MPB) were identified as Vibrio spp., Providencia sp., Bacillus sp., Shewanella sp., Staphylococcus sp., Planococcus sp., Salinococcus sp., and Glutamicibacter sp. Maximum melanin production was exhibited by Vibrio alginolyticus Marine Microbial Reference Facility (MMRF) 534 (50 mg ml), followed by two isolates of Vibrio harveyi MMRF 535 (40 mg ml) and MMRF 546 (30 mg ml). Using pathway inhibition assay and FT-IR spectral analysis, we identified the melanin secreted into the culture medium of MPB as 1,8-dihydroxynaphthalene-melanin. The bacterial melanin was non-cytotoxic to mouse fibroblast L929 cells and brine shrimps up to a concentration of 200 and 500 ppm, respectively. Bacterial melanin showed antioxidant activity at very low concentration (IC-9.0 ppm) and at 50 ppm, melanin protected L929 cells from UV-induced intracellular reactive oxygen stress. Our study proposes sponge-associated bacteria as a potential source of non-cytotoxic melanin with antioxidant potentials.

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Cholera outbreaks are prevalent in countries with a low Human Development Index (HDI) where people have limited access to safe drinking water, sanitation and hygiene (WASH). Intriguingly, the state of Kerala which records the highest HDI in India is endemic to cholera. We discuss the epidemiology of a cholera outbreak reported among migrant workers of Kerala in 2017. Virulence genes of Vibrio cholerae, toxR and ctxA, were detected in the river and ground water samples collected from the outbreaks sites which indicates need of enhanced awareness on WASH practices among migrant workers. The pathogenic Vibrio cholerae isolated from four patients in two districts had a similar DNA band pattern when analysed using repetitive extragenic palindromic-PCR (BOX), which indicates their single clonal origin. The four isolates were serotyped as O1 Ogawa. These isolates were resistant to multiple antibiotics including the carbapenem like imipenem. Nevertheless, isolates of these pathogenic bacteria were susceptible to tetracycline, identical to clinical isolates of Vibrio cholera reported earlier from this region. The current study highlights the importance of generating awareness on WASH protocols among migrant workers to prevent the outbreaks and considers community-based data as socioeconomic variable to predict the incidence of cholera.