High turnover rates of aerobic anoxygenic phototrophs in European freshwater lakes

Abstract

Aerobic Anoxygenic Phototrophic (AAP) bacteria are bacteriochlorophyll (BChl) a -containing organisms which use light energy to supplement their predominantly heterotrophic metabolism. Here, we investigated mortality and growth rates of AAP bacteria in three different freshwater lakes in Central Europe: the mountain lake Plešné, the oligo-mesotrophic Lake Stechlin and the forest pond Huntov. The mortality of AAP bacteria was estimated from diel changes of BChl a fluorescence. Net and gross growth rates were calculated from the increases in AAP cell numbers. The gross growth rates of AAP bacteria ranged from 0.38 to 5.6 d , with the highest values observed during summer months. Simultaneously, the rapidly growing AAP cells have to cope with an intense grazing pressure by both zooplankton and protists. The presented results document that during the day, gross growth usually surpased mortality. Our results indicate that AAP bacteria utilize light energy under natural conditions to maintain rapid growth rates, which are balanced by a generally intense grazing pressure.

Multiple Strategies for Light-Harvesting, Photoprotection, and Carbon Flow in High Latitude Microbial Mats

“…In this northern lake, the microbial mats face continuous light exposure in summer but a lower UV index due to the lower incidence angle of the light compared to the low Arctic mat. The larger proportion of phototrophic genes and pigments is consistent with the positive correlation between anoxygenic phototroph abundance and day length in freshwater environments (Cepáková et al, 2016; Garcia-Chaves et al, 2016) and suggests that the total duration of light exposure rather than maximum UV irradiance may shape community structure and pigmentation. The metabolic potential for photoprotective pigment synthesis was common to both microbial mat communities, suggesting that most cells in the consortia are protected from at least part of the damage from the long daily exposure to solar radiation (Figure 3).…”

Diel changes and diversity of pufM expression in freshwater communities of anoxygenic phototrophic bacteria

“…In previous studies, it was suggested that the decline of BChl a concentration was caused by the inhibition of de novo BChl a synthesis by light 34,35 . This has been documented under laboratory conditions 36 , however, it cannot be assumed that the same mechanism is present in a whole community of APB.…”

Light enhances the growth rates of natural populations of aerobic anoxygenic phototrophic bacteria

“…In addition, Kirchman and Hanson (2013) used theoretical calculations of the contribution of phototrophy to the organisms' energy requirements to conclude that even though AAP bacteria harvest more light energy than PR-bacteria, the net yield of phototrophy is only modest. Nevertheless, a positive correlation between AAP abundance and day length was found in seasonal studies in Mediterranean coastal waters and a lagoon (Lamy et al, 2011;Ferrera et al, 2014), and, recently, Cepáková et al (2016) observed that the GRs of AAP bacteria in lakes were higher than their mortality rates during the day, an indication that light may directly stimulate AAP growth. Contrarily, no clear effect was found in the activity of AAPs in short-term experiments neither in marine nor in freshwater environments (Stegman et al, 2014;Garcia-Chaves et al, 2016).…”