TlpC, a novel chemotaxis protein in Rhodobacter sphaeroides, localizes to a discrete region in the cytoplasm.

TlpC is encoded in the second chemotaxis operon of Rhodobacter sphaeroides. This protein shows some homology to membrane-spanning chemoreceptors of many bacterial species but, unlike these, is essential for R. sphaeroides chemotaxis to all compounds tested. Genomic replacement of tlpC with a C-terminal gfp fusion demonstrated that TlpC localized to a discrete cluster within the cytoplasm. Immunogold electron microscopy also showed that TlpC localized to a cytoplasmic electron-dense region. Correct TlpC-GFP localization depended on the downstream signalling proteins, CheW3, CheW4 and CheA2, and was tightly linked to cell division. Newly divided cells contained a single cluster but, as the cell cycle progressed, a second cluster appeared close to the initial cluster. As elongation continued, these clusters moved apart so that, on septation, each daughter cell contained a single TlpC cluster. The data presented suggest that TlpC is either a cytoplasmic chemoreceptor responding to or integrating global signals of metabolic state or a novel and essential component of the chemotaxis signalling pathway. These data also suggest that clustering is essential for signalling and that a mechanism may exist for targeting and localizing proteins within the bacterial cytoplasm.

Apparent bioaccumulation of Mn derived from paper-mill effluent by the freshwater crayfish Cherax destructor--the role of Mn oxidising bacteria.

Bioaccumulation studies of wastewater from a thermo-mechanical paper mill using the freshwater crayfish (Cherax destructor) consistently demonstrated elevated levels of manganese. Most of the Mn appeared to be associated with the carapace of the animals. It is suggested that the elevated Mn levels are the result of Mn-oxidising bacteria forming biofilms on the carapace of the crayfish followed by Mn oxide precipitation rather than active uptake of Mn by the crayfish.