Exopolysaccharides directed embellishment of diatoms triggered on plastics and other marine litter

www.nature.com/scientificreports OPEN Exopolysaccharides directed embellishment of diatoms triggered on plastics and other marine litter Mohd Jahir Khan1, Ramesh Singh2, Kunal Shewani3, Prashant Shukla3,5, P. V. Bhaskar4, Khashti Ballabh Joshi2,5 & Vandana Vinayak1* In the present study, embellishment or beautification of diatoms on substrates like plastics, polydimethylsiloxane, graphite, glass plate, and titanium dioxide, triggered by exopolysaccharides was examined under laboratory conditions. Exopolysaccharides are secreted mainly by primary colonisers, bacteria, which is succeeded by secondary colonisers i.e. diatoms. Both diatom (Nitzschia sp.4) and bacteria (Bacillus subtilis) were exposed with substrates separately for 30 days. Diatoms adhere on substrates strongly, not only because of surface roughness of different substrates but also the nanoporous architecture of diatoms which enhanced their embellishment. This study attempted to identify the substrates that adhere to diatoms strongly and was mainly analyzed by scanning electron microscope and further the observations are well supported by math work software (MATLAB). The variation of diatom’s binding on different substrates is due to the influence of marine litters on diatom population in ocean beds where they undergo slow degradation releasing macro, micro and nanoparticles besides radicals and ions causing cell death. Therefore a proof-of-concept model is developed to successfully deliver a message concerning benefit of using different diatom species. With the widespread use of plastics, the current era is known as Plasticene e ra1. Plastics are more common in human inhabited regions2–4 and it is estimated that about 5.25 trillions of plastics as small as 10 mm in size contaminate the oceans5.The process of plastic degradation is slow, takes around 300–400 years6. It degrades into microplastics and nanoplastics on exposure to UV radiations, waves and mechanical a brasion7,8. In addition, many other persistent materials including rubber, metals and glasses are disposed or abandoned in the marine and coastal environments to form marine litter (ML)9. These litters tend to sink in water and remain there for long time. Although they break into smaller fragments but are not degraded completely10. The litter sinking capability is enhanced by biofilms formed on their surfaces that increases the weight and let them sink in the ocean b eds11. These biofilms are exopolysaccharides (EPS) produced mainly by bacteria, microalgae and cyanobacteria12,13, protists14,15, fungi16,17and yeasts18. The first approachable colonizers on ML are generally bacteria followed by microalgae of which diatoms play a very important r ole19,20. The deposition or adhesion properties of diatoms on the ML is because of EPS produced by diatoms just like in bacteria21,22. EPS play important roles in maintaining the structural integrity of biofilms23. However, distribution of EPS in different microorganisms may show heterogeneity24. Cooksey reported that diatoms embellish themselves on steel and glass after few hours of exposure which follows increased growth due to photosynthetic activity25,26. Furthermore, colonization on Update 03 February 2021 The version of this Article previously published quoted an incorrect email address for Vandana Vinayak. Correspondence and requests for materials should also be addressed to kapilvinayak@gmail. com. This has now been corrected in the HTML and PDF versions of the Article. 1 Diatom Nanoengineering and Metabolism Laboratory (DNM), School of Applied Sciences, Dr. Harisingh Gour Central University, Sagar, Madhya Pradesh 470003, India. 2Department of Chemistry, School of Chemical Science and Technology, Dr. Harisingh Gour Central University, Sagar, Madhya Pradesh 470003, India. 3Department of Physics, School of Physical and Mathematical Sciences, Dr. Harisingh Gour Central University, Sagar, Madhya Pradesh 470003, India. 4National Centre for Polar and Oceanic Research, Vasco Da Gama, Goa 403804, India. 5These authors contributed equally: Prashant Shukla and Khashti Ballabh Joshi. *email: kapilvinayak@ gmail.com Scientific Reports | (2020) 10:18448 | https://doi.org/10.1038/s41598-020-74801-7 1 Vol.:(0123456789) www.nature.com/scientificreports/ hydrophobic surfaces is more rapid than the hydrophilic ones. The degree of anchorage depends upon the surface roughness of ML and EPS produced by diatoms and b acteria27–29. Biofilming on ML brings diverse changes not only in the ecological niches of marine flora and fauna but also in the e nvironment30,31. Diatoms besides biofilming the ML that enhances the sinking of pollutants in the water bodies fix almost 25% of global CO232. They meet 30% of world’s needs for crude oil, due to lipid rich bodies in their cells33. Furthermore, diatoms are nature’s freely available silica which has wide applications in forensics, and material science34–36. Thus, any change in the diversity of diatoms by ML not only alters both the atmospheric as well as benthic carbon c ycle37,38 but also change natural reservoir for many high and low value m etabolites39. Marine environment is aggressive towards plastics, polymers, glass and metals which are hazardous for marine life40,41. Earlier we reported how morphology of diatom, Gomphonema augur, showed valve deformation due to presence of trace metal analytes in water42. It is well established that different types of environmental pollutants influence diatom cell density, lipid composition and morphology43. This study showed that EPS of diatoms and bacteria play an important role in the adherence on ML. The diatom embellishes in different patterns onto ML due to its varied surface roughness and EPS secreted by diatoms either alone or in association with b acteria44. In shallow coastal waters, this may result in photochemical hydrolysis of plastics burgeoning into micro and nanoplastics thus disturbing marine ecology including distribution of bacteria and important phytoplanktons like diatoms45–48. Materials and methods Screening of diatom and bacteria for EPS content by FT‑IR. Diatoms and bacteria with maximum EPS were selected for adhesion on plastics and other substrates. In order to examine EPS released by different diatom taxon, surface functional groups of closely related species of Nitzschia sp. 1(NS1), Nitzschia sp. 3(NS3), Nitzschia sp. 4 (NS4), Pinnularia borealis (PB) and Gomphonema parvulum(GP) were studied. This was firstly done by FT-IR of these diatoms grown at day 1 and 30 in a modified f/2 media49,50. In order to grow bacteria environmental water samples was cultured on Luria Bertani agar m edium51 and different bacteria were identified 52,53 morphologically and b iochemically . To select the bacteria with highest EPS, FT-IR of all the bacterial samples was done after 24 h of growth. The method was based on a systematic treatment of FT-IR spectra obtained from dried bacterial and diatom samples54. The sel (...truncated)