Retention and release of Cryptosporidium parvum oocysts by experimental biofilms composed of a natural stream microbial community

Abstract

Cryptosporidium parvum oocysts accumulate on biofilm surfaces. The percentage of oocysts attached to biofilms remained nearly constant while oocysts were supplied to the system but decreased to a new steady-state level once oocysts were removed from the feed. More oocysts attached to summer biofilm cultures than winter biofilm cultures.

FIG. 1.

Top-down projection (A) and cross-sectional view (B) of a summer biofilm culture, with C. parvum oocysts attached at the biofilm surface. Biofilm cells are stained green with SYTO 9; oocysts are stained red with Cy3. The white line in panel A indicates the location of the cross section shown in panel B. Direction of water flow is from right to left. The biofilm is approximately 24-μm thick; oocysts are located 16 μm above the biofilm base.

FIG. 2.

Cumulative percentage of oocysts (±SE; n = 2) associated with the biofilm. The cumulative number of oocysts in the biofilm each day was calculated by adding the daily differences between the number of oocysts in the effluent and influent. This number was converted to a percentage by dividing by the cumulative number of influent oocysts. The biofilm accumulation on the last day was determined from the oocysts collected and counted directly from the biofilm, which agreed with the number calculated using the above-described method. Time zero indicates when the flow began; biofilm growth began 24 h earlier by seeding with microbial concentrate at zero flow. The solid black line on the x axis indicates the period of oocyst addition to the inflow. Error bars are smaller than symbols where not visible.