Publications

4420

Abstract Candidatus Accumulibacter phosphatis is an important microorganism for enhanced biological phosphorus removal (EBPR). In a previous study, we found a remarkable flexibility regarding salinity, since this same microorganism could thrive in both freshwater- and seawater-based environments, but the mechanism for the tolerance to saline conditions remained unknown. Here, we identified and described the role of trehalose as an osmolyte in Ca. Accumulibacter phosphatis. A freshwater-adapted culture was exposed to a single batch cycle of hyperosmotic and hypo-osmotic shock, which led to the release of trehalose up to 5.34 mg trehalose/g volatile suspended solids (VSS). Long-term adaptation to 30% seawater-based medium in a sequencing batch reactor (SBR) gave a stable operation with complete anaerobic uptake of acetate and propionate along with phosphate release of 0.73 Pmol/Cmol, and complete aerobic uptake of phosphate. Microbial analysis showed Ca. Accumulibacter phosphatis clade I as the dominant organism in both the freshwater- and seawater-adapted cultures (> 90% presence). Exposure of the seawater-adapted culture to a single batch cycle of hyperosmotic incubation and hypo-osmotic shock led to an increase in trehalose release upon hypo-osmotic shock when higher salinity is used for the hyperosmotic incubation. Maximum trehalose release upon hypo-osmotic shock was achieved after hyperosmotic incubation with 3× salinity increase relative to the salinity in the SBR adaptation reactor, resulting in the release of 11.9 mg trehalose/g VSS. Genome analysis shows the possibility of Ca. Accumulibacter phosphatis to convert glycogen into trehalose by the presence of treX, treY, and treZ genes. Addition of trehalose to the reactor led to its consumption, both during anaerobic and aerobic phases. These results indicate the flexibility of the metabolism of Ca. Accumulibacter phosphatis towards variations in salinity. Key points • Trehalose is identified as an osmolyte in Candidatus Accumulibacter phosphatis. • Ca. Accumulibacter phosphatis can convert glycogen into trehalose. • Ca. Accumulibacter phosphatis clade I is present and active in both seawater and freshwater.

"Candidatus Liberibacter solanacearum" is a gram-negative, fastidious bacterium that inhabits and multiplies in the phloem of host plants. The bacterium causes economically important diseases of solanaceous crops such as "zebra chips" of potatoes, and chlorotic weakening of cultivated plants of the Apiaceae family. Beside potatotes, this pathogen causes significant economic losses in tobacco, peper and tomato production. Insect vectors classified in the family Triozidae play an important role in the epidemiology of this bacterium. Insects transfer bacterial cells from infected to healthy plants by feeding on the plant juice from the phloem tissue. This pathogenic bacterium could be transmitted by infected seeds which result in long-distance spread. Based on the analysis of single nucleotide polymorphism (SNP), nine haplotypes (A, B, C, D, E, F, G, H, U) from different geographical regions, host plants and insect vectors have been described. Considering to impossibility of isolation of this bacterium on a nutrient medium, detection and identification are based on the application of molecular methods (conventional PCR, real-time PCR, multiplex PCR, nested PCR and LAMP PCR). Taking into consideration the increasing spread of "Candidatus Liberibacter solanacearum" in Europe, as well as its recent detection in Serbia, the aim of this paper was to raise an awareness about importance of this bacterium and summarize the protocols and molecular methods for its detection and identification.