Validation of droplet digital PCR for the detection and absolute quantification of Borrelia DNA in Ixodes scapularis ticks.

We evaluated the QX200 Droplet Digital PCR (ddPCR™, Bio-Rad) system and protocols for the detection of the tick-borne pathogens Borrelia burgdorferi and Borrelia miyamotoi in Ixodes scapularis nymphs and adults collected from North Truro, Massachusetts. Preliminary screening by nested PCR determined positive infection levels of 60% for B. burgdorferi in these ticks. To investigate the utility of ddPCR as a screening tool and to calculate the absolute number of bacterial genome copies in an infected tick, we adapted previously reported TaqMan®-based qPCR assays for ddPCR. ddPCR proved to be a reliable means for detection and absolute quantification of control bacterial DNA with precision as low as ten spirochetes in an individual sample. Application of this method revealed the average carriage level of B. burgdorferi in infected I. scapularis nymphs to be 2291 spirochetes per nymph (range: 230-5268 spirochetes) and 51 179 spirochetes on average in infected adults (range: 5647-115 797). No ticks naturally infected with B. miyamotoi were detected. The ddPCR protocols were at least as sensitive to conventional qPCR assays but required fewer overall reactions and are potentially less subject to inhibition. Moreover, the approach can provide insight on carriage levels of parasites within vectors.

The efficiency of the CO2-concentrating mechanism during single-cell C4 photosynthesis.

The photosynthetic efficiency of the CO(2)-concentrating mechanism in two forms of single-cell C(4) photosynthesis in the family Chenopodiaceae was characterized. The Bienertioid-type single-cell C(4) uses peripheral and central cytoplasmic compartments (Bienertia sinuspersici), while the Borszczowioid single-cell C(4) uses distal and proximal compartments of the cell (Suaeda aralocaspica). C(4) photosynthesis within a single-cell raises questions about the efficiency of this type of CO(2) -concentrating mechanism compared with the Kranz-type. We used measurements of leaf CO(2) isotope exchange (Δ(13) C) to compare the efficiency of the single-cell and Kranz-type forms of C(4) photosynthesis under various temperature and light conditions. Comparisons were made between the single-cell C(4) and a sister Kranz form, S. eltonica[NAD malic enzyme (NAD ME) type], and with Flaveria bidentis[NADP malic enzyme (NADP-ME) type with Kranz Atriplicoid anatomy]. There were similar levels of Δ(13) C discrimination and CO(2) leakiness (Φ) in the single-cell species compared with the Kranz-type. Increasing leaf temperature (25 to 30 °C) and light intensity caused a decrease in Δ(13) C and Φ across all C(4) types. Notably, B. sinuspersici had higher Δ(13) C and Φ than S. aralocaspica under lower light. These results demonstrate that rates of photosynthesis and efficiency of the CO(2) -concentrating mechanisms in single-cell C(4) plants are similar to those in Kranz-type.