The effects of N:P ratio and nitrogen form on four major freshwater bacterial taxa in biofilms

Abstract

Bacteria in freshwater systems play an important role in nutrient cycling through both assimilatory and dissimilatory processes. Biotic and abiotic components of the environment affect these transformations as does the stoichiometry of the nutrients. We examined responses of four major taxa of bacteria in biofilms subjected to various N:P molar ratios using either nitrate or ammonium as a nitrogen source. Fluorescent in situ hybridization was used to enumerate the Domain bacteria as well as the alpha-, beta-, and gamma-proteobacteria, and the Cytophaga-Flavobacteria cluster. Generally, bacterial responses to the treatments were limited. However, the Cytophaga-Flavobacteria and beta-proteobacteria both responded more to the ammonium additions than nitrate, whereas, the alpha-proteobacteria responded more to nitrate additions. The beta-proteobacteria also exhibited peak relative abundance at the highest N:P ratio. Nutrient concentrations were significantly different after the incubation period, and there were distinct changes in the stoichiometry of the microcosms with ammonium. We demonstrated that bacteria may play an important role in nutrient uptake, and transformation, and can have a dramatic effect on the nutrient stoichiometry of the surrounding water. However, although some taxa exhibited differences in response to ammonium and nitrate, the impact of nutrient stoichiometry on the abundance of the taxa examined was limited.

Planktonic Bacterial Responses to Nutrient Amendments in Wetland Mesocosms

“…The lack of response by any bacterial taxa examined to the nutrient amendments was unexpected, since bacterial growth has been shown to be stimulated by nutrients (Brett et al 1999). The 6-day incubation period should have been sufficient for bacterial community changes, as similar changes to nutrient amendments in our lab and others have been observed within 3-6 days (Burns and Schallenberg 1998;Fisher et al 2000;Olapade and Leff 2006;Barlett and Leff 2010). However, there are many other factors that can affect bacterial communities, including the availability and recalcitrance of carbon (Carlson et al 2002;Olapade and Leff 2005).…”

“…Our previous work suggests that there are interactions between bacteria, nutrient stoichiometry, and form (Rubin and Leff 2007;Barlett and Leff 2010). Although correlative relationships were observed in our field survey (Rubin and Leff 2007) and other similar studies (Olapade and Leff 2004;Gao 2005), the cause and effect relationships cannot be proven.…”

“…The 6 day duration was chosen as a time period in which bacterial community changes have been seen while minimizing enclosure effects (Pace and Funke 1991;Fisher et al 2000;Lebaron et al 2001). Also, this time period allowed us to compare directly with previous experiments from our lab Leff 2006, Barlett andLeff 2010). Experiments (following this same design) were repeated on different dates with varying types of N and P (e.g., organic versus inorganic) as detailed in Table 2.…”

Bacterial and Phytoplankton Responses to Nutrient Amendments in a Boreal Lake Differ According to Season and to Taxonomic Resolution

“…Still there is a wide variation in nutrient requirements between organisms and although functional differentiation within bacterial taxa has been recognized [18]–[20], available techniques have not previously enabled detailed resolution of potentially ecologically coherent groups. Hence conclusions regarding nutrient limitation have been drawn for rather broad and diverse groups; for example, that Actinobacteria do not respond to carbon [21] and that Betaproteobacteria respond to ammonium but not to nitrate [22]. However, while the total community or even broad phyla might be experiencing co-limitation by N and P, the individual community members or populations could be limited by only one element [10], since taxa within a phylum are not necessarily functionally or metabolically coherent.…”

Bacterial degradation of dissolved organic matter released by Planktothrix agardhii (Cyanobacteria)

“…Organisms of the class Alphaproteobacteria, order Rhizobiales (represented by the genera Caulobacter, Shinella, and possibly Novosphingobium) were found mainly during the slower phase of degradation, when nutrient availability consisted only in more refractory compounds at limiting amounts, reflecting the group usual dominance in oligotrophic systems (Barlett and Leff, 2010). Bagatini et al (2014) also found increasing proportions of Alphaproteobacteria associated with two Cyanobacteria along cultivation time and the genus Novosphingobium has already been associated with high concentrations of recalcitrant compounds .…”