Effects of prey abundance and light intensity on the mixotrophic chrysophyte Poterioochromonas malhamensis from a mesotrophic lake

Abstract

1. Previous studies of mixotrophy in the flagellate Poterioochromonas malhamensis (Chrysophyceae) were performed on strains that had been in culture for > 30 years. This study aims to compare mixotrophy in a cultured strain with one recently isolated from a mesotrophic lake (Lacawac) in Pennsylvania, U.S.A. 2. P. malhamensis from the lake exhibited a nutritional flexibility similar to that of the culture strain, growing phototrophically but inefficiently in comparison to other nutritional modes (growth rate (μ) = 0.015 h−1). Supplementing an inorganic salts medium with 1 mM glucose resulted in a doubling of μ to 0.035 h−1 and 0.033 h−1 in the light and the dark, respectively. Addition of an algal prey, Nannochloris, to the inorganic salts medium increased growth to rates similar to those observed with glucose. Maximum growth of the lake strain, 0.095 h−1, was achieved when bacteria was supplied as food. During growth on bacteria, cellular chlorophyll a (Chl a) decreased from 140 fg cell−1 to 10 fg cell−1 over 22 h when cultured either in the light or dark. In illuminated cultures, cell‐specific Chl a concentration recovered to 185 fg cell−1 after bacteria became limiting. 3. In contrast to the cultured strain, however, the lake isolate exhibited an inverse relationship between light intensity and ingestion rate. Calculated grazing rates, based upon the ingestion of fluorescently labeled bacteria, were 3.2, 5.2 and 9.4 bacteria flagellate−1 h−1, for P. malhamensis incubated in high light, low light and darkness, respectively. Phagotrophy is thus influenced by a light regime in this predominately heterotrophic mixotroph.

Importance of bacterivory by pigmented and heterotrophic nanoflagellates during the warm season in a subtropical western Pacific coastal ecosystem

“…To date, there are not enough data to support a clear explanation for PNF ingestion of bacteria at a given site. A range of environmental factors (nutrients, light, prey abundance) may all affect the abundance and feeding behavior of PNF (Bird & Kalff 1986, Salonen & Jokinen 1988, Caron et al 1993, Nygaard & Tobiesen 1993, Holen 1999, Sanders et al 2000, Moorthi & Berninger 2006, Unrein et al 2007). In most cases, photosynthesis would presumably be the primary energy source for these PNF, while phagotrophy would allow them to compete successfully with non-phagotrophic algae for growth-limiting nutrients.…”

“…However, a range of environmental factors, including light, prey abundance and nutrients, can affect the feeding behavior of PNF and it is unlikely that there is a single explanation or a universal stimulus for the ingestion of particles by PNF (Bird & Kalff 1986, Salonen & Jokinen 1988, Caron et al 1993, Nygaard & Tobiesen 1993, Holen 1999, Moorthi & Berninger 2006, Unrein et al 2007). In some studies, PNF feeding rates have been found to increase in low-light conditions or in darkness (Hall et al 1993, Holen 1999), but to decrease under limited light conditions in other studies (Caron et al 1993, Jones & Rees 1994. One analysis found that light had no effect at all on the feeding rates of PNF (Sanders et al 2001).…”

Mixotrophic nanoflagellates in coastal sediments in the western Baltic Sea

“…Light limitation, for instance, has been shown to have disparate effects on planktonic mixotrophs, depending on species identity and on environmental factors such as nutrient availability and prey abundances. Some laboratory studies demonstrated increasing feeding rates in bacterivorous MNF under light limitation (Veen 1991, Holen 1999, while others revealed lower ingestion rates under low light conditions or darkness (Caron et al 1993, Jones & Rees 1994 or no effects of light at all (Andersson et al 1989, Sanders et al 1990). In field studies of plankton, MNF abundances were related to low light intensities in some cases (Bird & Kalff 1986, Pålsson & Granéli 2004, while in others MNF abundances seemed to be more dependent on other factors, such as water temperature (Bird & Kalff 1987) and nutrient availability (Nygaard & Tobiesen 1993, Arenovski et al 1995.…”

“…The types of mixotrophy reported range along a gradient from nearly pure phototrophy to nearly pure heterotrophy (Jones 1994). In addition, changes in environmental parameters such as light level, nutrient concentration and prey abundance may cause shifts within a species in the relative importance of photosynthesis and phagotrophy (Nygaard & Tobiesen 1993, Jones 1997, Holen 1999. Therefore, a taxonomic characterization of the microbial community alone does not provide information concerning phagotrophic activity of mixotrophic algae because this activity can be induced or suppressed by a variety of conditions.…”

Exploring strategies for nanoflagellates living in a ‘wet desert’

“…For instance, in the case of Poterioochromonas malhamensis this argument was used in regard to Type Strain 933/1a (e.g. Holen 1999, Pålsson & Daniel 2004), but careful re-evaluation of the data showed that the findings on the different strains used in the laboratory studies were not contradictory at all (see subsection on the contribution of phototrophy; see also Pringsheim 1952) and that only the interpretation of the results differed. In effect, even a 60 yr old laboratory strain still responds in the same way as recently isolated strains.…”