ISA 2016 Matera 29 Maggio – 1 Giugno 2016 Purple photosynthetic bacteria and sea urchin coelomocytes examination by X‐ray photoelectron spectroscopy as a non‐conventional analytical technique for bio‐organic materials , Livia Giotta , Patrizia Pagliara1, Daniela Chirizzi2, Simona Rella1, Disma Mastrogiacomo1, F. Milano3 1,2*
Maria Rachele Guascito
1
1
Dipartimento di Scienze e Tecnologie Biologiche e Ambientali, Università del Salento, 73100 Lecce, Italy 2
Istituto di Scienze dell'Atmosfera e del Clima, ISAC‐CNR, 73100 Lecce, Italy 3
Istituto per i Processi Chimico Fisici, UOS Bari, Via Orabona 4, 70126 Bari, Italy In this study, we report some preliminary results on the X‐ray photoelectron spectroscopy (XPS) characterization of photosynthetic bacteria and sea urchins coelomocytes. XPS spectroscopy is a surface technique that allows to analyze, in terms of chemical speciation, all elements, with the exception of H and He, present in different typologies of solid samples (inorganic and organic), as long as their atomic percent concentrations (At.%) are not below 0.01‐0.1%, depending on the specific element. This technique potentially can also allow to obtain chemical imaging of surfaces with lateral resolution of 3m. However, at the state of the art, the employment of this analytical technique as a non‐conventional tool for the investigation of bio‐organic materials (i.e. microorganisms and their related systems such as biofilms, extracellular polymeric substances (EPS) and bio‐adhesions), has been reported only in a limited number of papers[1]. The XPS characterization of purple photosynthetic bacteria (Rhodobacter sphaeroides), able to interact with detrimental heavy metal ions, such as nickel and chromium has been performed, leading to the successful detection of both metal immobilization and surface modifications induced by the environmental stress. Measurements revealed that treatment with Ni2+ results in full displacement of K+ ions from R. sphaeroidesbacterial surfaces, indicating high affinity between nickel ions and surface functional groups. Moreover the detection of chromium(III) onto R. sphaeroidescells (Figure 1) incubated with chromate ions allowed to confirm the potential of this phototrophic bacterium as bio‐catalyst for the reduction of chromate to the less toxic trivalent form Furthermore, the sea urchin Arbacia lixula coelomocyte population is characterized by the presence of red cells, which number may increase in response to different stress. As red spherula cells accumulate around injuries and sites of infection, this analysis may help to understand what is the role of cell surface interacting with bacteria in addition to the action of echinochrome A present inside the cells. In particular, here we compare the red cells coelomocytes surface with the white ones, highlighting a quite different surface chemical composition. ISA 2016 Matera 29 Maggio – 1 Giugno 2016 (C)
HR Cr 2p3/2 _ Rodobacter sphaeroides _ Cr(III) cell
Intensity (a.u.)
Cr(III)
588
583
578
Binding Energy (eV)
573
568
Figure 1. Cr 2p XPS peaks from R. sphaeroides cells after Cr(VI) exposure and attributed to Cr(III)[2]. References 1. Rouxhet and Genet, Surf. Innterface Anal. 2011, 43,1453. 2. Biesinget et al., Surf. Interface Anal. 2004, 36, 1550.