Quantification of purple non-sulphur phototrophic bacteria and their photosynthetic structures by means of total reflection X-ray fluorescence spectrometry (TXRF)

Phototrophic bacteria are metabolically diverse microorganisms that attract substantial attention due to their growing potential in scientific and industrial applications. In the present study, total reflection X-ray fluorescence (TXRF) spectrometry was applied to perform a comprehensive analysis of the trace elements content of purple non-sulphur phototrophic bacteria, their chromatophores and selected photosynthetic structures in response to alterations in oxygen growth conditions. There is a lack of consistent information on the content of microelements, their distribution and in particular correlations between them. This analysis, carried out on the Rhodobacter sphaeroides species aims to rectify this. Qualitative examination revealed the presence of microelements generally not considered as basic in the bacterial ionome. Quantitative inspection pointed to Fe as the major trace element in this phototrophic species irrespective of growth conditions (sample type). The K/Rb and Ca/Sr ratios were determined for the first time for bacteria and their photosynthetic membranes. Finally, the ionomic approach to elemental accumulation followed by statistical analysis revealed intriguing relationships between the elements within cells and phototrophic membranes. The vast potential and usefulness of the TXRF technique in a wide range of biological and environmental applications is underlined.