Rotifers weaken the efficiency of the cyanobacterium defence against ciliate grazers

ABSTRACT Cyanobacteria can protect themselves through limited dispersion and by increasing the compactness of the mucilage-covered cyanobacterial mat as well as by producing sheaths covering their trichomes. These features have been used in research to measure their degree of inducible defence. The influence of the presence of the rotifers Lecane inermis on the effectiveness of Phormidium sp. (Ph2) cyanobacterium defence was investigated. Experiments were conducted on the ciliates Pseudomicrothorax dubius and Furgasonia blochmanni, specialised in the ingestion of filamentous cyanobacteria. The most compact were cyanobacterial mats that were subjected exclusively to ciliates and the most dispersed were mats in the presence of rotifers alone. The presence of rotifers feeding on cyanobacterial mucilage led to the decreased effectiveness of the defence in two ways, by increasing the dispersion of cyanobacterial trichomes, thus loosening the cyanobacterial mat, and through the ingestion of the exopolysaccharide material covering the trichomes. As a result, in the presence of rotifers and the high density of ciliates, almost all the trichomes were removed. Moreover, in comparison with other treatments, a higher number of ciliates and rotifers remained active until the end of the experiments. This is the first report to show how rotifers can weaken the defence of cyanobacteria.

The use of rotifers for limiting filamentous bacteria Type 021N, a bacteria causing activated sludge bulking

The excessive growth of filamentous bacteria and the resultant bulking of activated sludge constitute a serious problem in numerous wastewater treatment plants. Lecane inermis rotifers were previously shown to be capable of reducing the abundance of Microthrix parvicella and Nostocoida limicola in activated sludge. In the present study, the effectiveness of four Lecane clones in reducing the abundance of Type 021N filamentous bacteria was investigated. Three independent experiments were carried out on activated sludge from three different treatment plants. We found that Lecane rotifers are efficient consumers of Type 021N filaments.

Clonal variation in reproductive response to temperature by a potential bulking control agent, Lecane inermis (Rotifera)

The novel idea of using rotifers Lecane inermis (Rotifera, Monogononta) as a tool to overcome activated sludge bulking generates an on-going need to study rotifer biology. The results of biological research on rotifers can serve to improve the method so that it can be most effective when applied in treatment plants. The aim of this study was to test the effect of temperature on four selected rotifer clones originating from different treatment plants. The rate of population development from a single individual (parthenogenetic female) during a 10-day experiment was measured at three temperatures: 8, 15 and 20 °C. The temperatures used reflect the annual temperature distribution in the majority of municipal wastewater treatment plants in the temperate zone. The growth rate coefficient (r) and doubling time (tD) were calculated for each clone. Under the most favourable conditions (20 °C), r values varied between 0.41 and 0.47 d and doubling time between 1.5 and 1.7 d. At a temperature of 15 °C, the doubling time was approximately two times longer (2.5–3.4 d). The strongest intraspecific variations were observed at the lowest temperature of 8 °C. At this temperature, one of the clones almost failed to proliferate, and another exhibited a doubling time of 7.9 d. The doubling times were a few times greater for the remaining two clones (60 d for Lk1, 33.3 d for Lk4). These results could be very useful in predicting the chances that the rotifers would survive in a biological reactor in a wastewater treatment plant at the temperatures used in these reactors.

The effect of medium on selected life-history traits in three clones of Lecane inermis (Rotifera) from activated sludge

We tested the effect of various culture media on life-history traits in three clones of the rotifer Lecane inermis, a potential bulking control agent. Four types of media were tested: a filtrate of activated sludge, mineral water, and each of these media enriched with molasses. The number of live and dead individuals and the number of amictic eggs were counted during the 14-day experiment, and the egg ratio (ER) and mortality rate were calculated. We found that the rotifers were well adapted to the changes in chemical composition of the medium and that the addition of molasses resulted in a significant increase in rotifer abundance. The highest ER was noted after two days, reaching a maximum of 4 eggs per female in treatments with filtrate and molassesenriched filtrate. The life-history traits varied depending on the clone and the medium, but all of the clones were able to survive and proliferate, even after 14 days of starvation.