Pink‐ and orange‐pigmented Planctomycetes produce saproxanthin‐type carotenoids including a rare C45 carotenoid

Planctomycetes, are ubiquitous and environmentally important Gram-negative aquatic bacteria with key roles in global carbon and nitrogen cycles. Many planctomycetal species have a pink or orange colour and have been suggested to produce carotenoids. Potential applications as food colorants or anti-oxidants have been proposed. Hitherto, the planctomycetal metabolism is largely unexplored and the strain pigmentation has not been identified. For a holistic view on the complex planctomycetal physiology we analyzed carotenoid profiles of the pink-pigmented strain Rhodopirellula rubra LF2T and of the orange strain Rubinisphaera brasiliensis Gr7. During LC-MS/MS analysis of culture extracts we were able to identify three saproxanthin-type carotenoids including a rare C45 carotenoid. These compounds, saproxanthin, dehydroflexixanthin and 2’-isopentenyldehydrosaproxanthin, derive from the common carotenoid precursor lycopene and are characterized by related end groups, namely a 3-hydroxylated β-carotene-like cyclohexene ring as one end group and simple hydration on the other end of the molecule. Based on the observed molecule structure we present putative pathways for their biosynthesis. Results support Planctomycetes as a promising, yet mostly untapped source of carotenoids

Remediation of salt-affected soil by the addition of organic matter: an investigation into improving glutinous rice productivity

Soil salinity may limit plant growth and development, and cause yield loss in crop species. This study aimed at remediating saline soil using organic matter (OM) treatment, before the cultivation of RD6 rice (Oryza sativa L. spp. indica). Physiological and morphological characters of rice plants, as well as crop yield, were evaluated from salt-affected soil with varying levels of salinity. The chlorophyll a and total chlorophyll pigments of rice plants grown in salt-affected soil (2% salt level) with the application of OM were maintained better than in plants grown without OM treatment. The degree of reduced photosynthetic pigments in rice plants was dependent on the level of salt contamination. Pigment content was positively related to maximum quantum yield of PSII (Fv/Fm) and quantum efficiency of PSII (ΦPSII), leading to reduced net photosynthetic rate (Pn) and reduced total grain weight (TGW). Photosynthetic abilities, including chlorophyll a and total chlorophyll pigments and ΦPSII, in rice plants grown with OM treatment were greater than in those cultivated in soil without the OM treatment, especially in high salt levels (1-2% salt). The remediation of salt-affected soil in paddy fields using OM should be applied further, as an effective way of enhancing food crop productivity