Protozoans bacterivory in a subtropical environment during a dry/cold and a rainy/warm season

Abstract

In aquatic ecosystems, bacteria are controlled by several organisms in the food chain, such as protozoa, that use them as food source. This study aimed to quantify the ingestion and clearance rates of bacteria by ciliates and heterotrophic nanoflagellates (HNF) in a subtropical freshwater reservoir (Monjolinho reservoir - São Carlos - Brazil) during one year period, in order to verify their importance as consumers and controllers of bacteria in two seasons, a dry/cold and a rainy/warm one. For this purpose, in situ bacterivory experiments were carried out bimonthly using fluorescently labeled bacteria with 5-(4,6 diclorotriazin-2yl) aminofluorescein (DTAF). Although ciliates have shown the highest individual ingestion and clearance rates, bacterivory was dominated by HNF, who showed higher population ingestion rates (mean of 9,140 bacteria h−1 mL−1) when compared to ciliates (mean of 492 bacteria h−1 mL−1). The greater predation impact on bacterial communities was caused mainly by the small HNF (< 5 μm) population, especially in the rainy season, probably due to the abundances of these organisms, the precipitation, trophic index state and water temperature that were higher in this period. Thus, the protozoan densities together with environmental variables were extremely relevant in determining the seasonal pattern of bacterivory in Monjolinho reservoir.

Pro- and eukaryotic keystone taxa as potential bio-indicators for the water quality of subtropical Lake Dongqian

“…For instance, it has been shown that Microcystis, which accumulates in spring, is critical for the microbial community structure in aquatic ecosystems ( Zuo et al, 2021 ). The eukaryotic taxon Tintinnidium, which feeds on most bacteria, is an important biotic factor in regulating the bacterial community in aquatic ecosystems ( Hisatugo et al, 2014 ). The prokaryotic taxon HgcI clade that was found in summer could improve water quality due to its participation in N fixation and denitrification ( Ruprecht et al, 2021 ).…”

Molecular characterization of waterborne protozoa in surface water and sediment in Brazil: a taxonomic survey of ciliated protozoa and their correlation with Giardia duodenalis and Cryptosporidium spp.

“…The existence of a correlation between class 1 and 2 ciliates and temperature and dissolved oxygen highlights the presence of organic contamination in these sites, as high bacterial population densities are found in organically polluted environments, which contributes to an increase in temperature and a decrease in dissolved oxygen from the water, and the stimulation of the growth of the populations of bacterivorous ciliates. Recent studies (Hisatugo et al, 2014;Mansano et al, 2014) have demonstrated that heterototrophic ciliated protozoa and nano agellates present high rates of bacterial ingestion, representing an important bacterial control in the environment.…”

Combating Parasitic Nematode Infections, Newly Discovered Antinematode Compounds from Marine Epiphytic Bacteria

“…In addition, predation by heterotrophic protozoa and bacterivorous nematodes represents another biotic stress resulting in major mortality for both planktonic and surface-associated bacteria in the marine habitat ( Figure 1 ) [ 85 , 97 ]. Protozoans, for example Rhynchomonas nasuta and Cafeteria roenbergensis , are among the most abundant ubiquitous species in the ocean and are the major controllers of the food web in the marine environment through their function as bacterial predators [ 98 , 99 , 100 ]. Nematodes such as Pareudiplogaster pararmatus are among the natural consumers of organic biomass in benthic habitats actively grazing bacterial mats and the biofilms of biotic surfaces [ 101 , 102 ].…”