Candidatus “Thiodictyon syntrophicum”, sp. nov., a new purple sulfur bacterium isolated from the chemocline of Lake Cadagno forming aggregates and specific associations with Desulfocapsa sp.

Strain Cad16T is a small-celled purple sulfur bacterium (PSB) isolated from the chemocline of crenogenic meromictic Lake Cadagno, Switzerland. Long term in situ observations showed that Cad16T regularly grows in very compact clumps of cells in association with bacteria belonging to the genus Desulfocapsa in a cell-to-cell three dimensional structure. Previously assigned to the genus Lamprocystis, Cad16T, was here reclassified and assigned to the genus Thiodictyon. Based on comparative 16S rRNA gene sequences analysis, isolate Cad16T was closely related to Thiodictyon bacillosum DSM234T and Thiodictyon elegans DSM232T with sequence similarities of 99.2% and 98.9%, respectively. Moreover, matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS) analysis separated Cad16T from other PSB genera, Lamprocystis and Thiocystis. Major differences in cell morphology (oval-sphere compared to rod-shaped) and arrangement (no netlike cell aggregates), carotenoid group (presence of okenone instead of rhodopinal), chemolithotrophic growth as well as the ability to form syntrophic associations with a sulfate-reducing bacteria of the genus Desulfocapsa suggested a different species within the genus Thiodictyon.This isolate is therefore proposed and described as Candidatus “Thiodictyon syntrophicum” sp. nov., a provisionally novel species within the genus Thiodictyon.