Variation in composition and relative content of accumulated photopigments in a newly isolated Rhodobacter capsulatus strain XJ-1 in response to arsenic

Abstract

This study aimed to isolate and characterize a new arsenic (As)-tolerant bacterial strain (XJ-1) from the Halosol soil, to evaluate its As tolerance, and to examine the variation in composition and relative content of accumulated photosynthetic pigments in response to As. The experiments were performed with high-performance liquid chromatography (HPLC), inductively-coupled plasma mass spectrometry (ICP-MS), liquid chromatography/mass spectrometry (LC/MS), thin-layer chromatography (TLC) and grayscale intensity image analysis using Gel-Pro analyzer software. Strain XJ-1 was identified as Rhodobacter (R.) capsulatus based on 16S rRNA gene sequencing and physiological characteristics. Strain XJ-1 was able to grow when exposed to arsenite [As(III)] and arsenate [As(V)] under anaerobic-light conditions. The median effective concentrations (EC₅₀) of As(III) and As(V) were 0.61 mM and 2.03 mM, respectively. Strain XJ-1 could reduce As(V) to As(III), but As(III) could not be transformed back to As(V) or other organic As compounds. Accumulation of bacteriochlorophylls and carotenoids in strain XJ-1 varied in the presence of 0.2–1.2 mM As(III) and 0–2.5 mM As(V). As exposure resulted in pronounced variation in compositions and contents of photosynthetic pigments, especially hydroxyspheroidene, bacteriophaeophytin, the ratio of tetrahydrogeranylgeranyl to phytylated BChl a, and the ratio of spheroidene to spheroidenone. This research highlights the adaptative response of R. capsulatus strain XJ-1 photosystems to environmental As, and demonstrates the potential of utilizing the sensitivity of its photosynthetic pigments to As(III) and As(V) for the biodetection of As in the environment.

Keywords:

• Arsenic
• bacteriochlorophyll
• carotenoids
• Rhodobacter capsulatus

Additional information

Funding

This work was supported by the National Natural Science Foundation of China (Grant 31270106, 31070054), by National Natural Science Foundation of Fujian Province (Grant 2012J01136), by the Foundation of Key Laboratory of Urban Environment and Health, Institute of Urban Environment of Chinese Academy of Sciences (KLUEH201005).