Chemoreceptors in Sinorhizobium meliloti require minimal pentapeptide tethers to provide adaptational assistance.

Sensory adaptation in bacterial chemotaxis is mediated by posttranslational modifications of methyl-accepting chemotaxis proteins (MCPs). In Escherichia coli, the adaptation proteins CheR and CheB tether to a conserved C-terminal receptor pentapeptide. Here,we investigated the function of the pentapeptide motif (N/D)WE(E/N)F in Sinorhizobium meliloti chemotaxis. Isothermal titration calorimetry revealed stronger affinity of the pentapeptides to CheR and activated CheB relative to unmodified CheB. Strains with mutations of the conserved tryptophan in one or all four MCP pentapeptides resulted in a significant decrease or loss of chemotaxis to glycine betaine, lysine, and acetate, chemoattractants sensed by pentapeptide-bearing McpX and pentapeptide-lacking McpU and McpV, respectively. Importantly, we discovered that the pentapeptide mediates chemotaxis when fused to the C-terminus of pentapeptide-lacking chemoreceptors via a flexible linker. We propose that adaptational assistance and a threshold number of available sites enable the efficient docking of adaptation proteins to the chemosensory array. Altogether, these results demonstrate that S. meliloti effectively utilizes a pentapeptide-dependent adaptation system with a minimal number of tethering units to assist pentapeptide-lacking chemoreceptors and hypothesize that the higher abundance of CheR and CheB in S. meliloti compared to E. coli allows for ample recruitment of adaptation proteins to the chemosensory array.

Detection of a novel putative phlebovirus and first isolation of Dugbe virus from ticks in Accra, Ghana.

Ticks are ectoparasites that transmit various types of human and animal pathogens. In particular, emerging and re-emerging diseases caused by tick-borne viruses are public health concerns around the world. However, in many countries of the sub-Saharan African region, epidemiological information on tick-borne viral infections is limited, and their prevalence and distribution remain largely unknown. In this study, we conducted surveillance on ticks to detect medically important tick-borne bunyaviruses in three study sites in and near to Accra, the capital city of Ghana, in 2015. Domestic dogs and cattle were surveyed and were found to be infested with various tick species belonging to the genera Rhipicephalus, Amblyomma and Haemaphysalis. Importantly, we detected a novel putative phlebovirus in Rhipicephalus ticks, and successfully isolated a new strain of Dugbe virus from Am. variegatum ticks. To our knowledge, this is the first report of tick-associated viruses in Ghana other than Crimean-Congo hemorrhagic fever virus.