Amoebic grazing of freshwater Synechococcus strains rich in phycocyanin

Abstract

Fifteen strains of naked amoebae were presented with 19 strains of Synechococcus on an agar surface. After 14 days of incubation, each of the 285 combinations yielded one of three responses. 42.1% of combinations showed clearing (digestion) of the Synechococcus (C), 56.5% of combinations showed no clearing of the Synechococcus (N) while 1.4% of combinations showed partial clearing of the Synechococcus (P). In general, the Synechococcus strains showed variability in their susceptibility to digestion by the amoebae and the amoebae showed variability in their ability to digest the Synechococcus strains. There was no evidence for amoebae actively selecting profitable prey and equivalent-sized Synechococcus strains were ingested at the same rate, irrespective of their fate. There was some evidence of 'size-selective' grazing in that amoebae ingested the smaller Synechococcus strains at higher rates than the larger strains. However, there was no correlation between prey size and their ultimate fate. These data suggest that amoebae are not selective with regard to the ingestion of synechococci, but that 'selection' occurs at the digestion stage, i.e. whether the synechococci are digested or not.

Digestion of bacteria by the freshwater ciliate Tetrahymena pyriformis

“…Only 1 Gram positive bacterium was included in this study (Staphylococcus aureus), but we could speculate that reduced digestion, compared to Gram negative strains, is attributed to differences in cell wall structure as suggested by Nilsson (1987), González et al (1990) and Iriberri et al (1994), with Gram positive cell walls being thicker than those of Gram negative cells. Synechoccocus cells, although Gram negative, have even thicker cell walls (Golecki 1977) and this may have contributed to their resistance to digestion, not only in T. pyriformis, but also in amoebae (Pickup et al 2007, Dillon & Parry 2009). Vacuoles containing < 6 Synechococcus sp.…”

“…However, this predator-prey relationship is complex as some bacteria can prevent normal digestive processes within protozoan food vacuoles (Abu Kwaik et al 1998, Strahl et al 2001, whilst others can undergo the full digestive process and emerge apparently unharmed (Schlimme et al 1995, Pickup et al 2007, Dillon & Parry 2009). This latter phenomenon is poorly understood and may be a result of an active response by bacteria, as it is for pathogens (Abu Kwaik et al 1998), or selective or inefficient digestion by protozoa (González et al 1990).…”

Impairment of O-antigen production confers resistance to grazing in a model amoeba–cyanobacterium predator–prey system

“…Grazing affects both mortality and population structure (8), as has recently been observed in the rapid decline of biomass of Microcystis in a natural pond and in the restructuring of the bloom with a shift from a susceptible Microcystis species to a resistant one upon amoebal grazing (9). Whereas it is known that amoebae graze on cyanobacteria (10)(11)(12), these predators have not received much attention. Van Wichelen et al (2010) attribute this omission to the fact that population densities of amoebae peak for short periods of time and, hence, may be overlooked during monthly or even biweekly samplings of freshwater environments (9).…”

Heavy metal tolerance genes alter cellular thermodynamics inPseudomonas putidaand riverPseudomonas spp. and influence amebal predation

“…As the metal concentration increased to 1 and 10 μM cadmium, the wild type was consumed faster than both KT1 and KT4. This feeding behavior may be explained by the fact that ameba have been observed to consume smaller bacteria faster than larger bacteria (Dillon & Parry, ). Also, nanoflagellates, which can feed similarly to ameba (Xinyao et al ., ), were shown to preferentially graze smaller P. putida cells faster than larger cells (Fu et al ., ).…”