Acetate Degradation at Low pH by the Moderately Acidophilic Sulfate Reducer Acididesulfobacillus acetoxydans gen. nov. sp. nov.

In acid drainage environments, biosulfidogenesis by sulfate-reducing bacteria (SRB) attenuates the extreme conditions by enabling the precipitation of metals as their sulfides, and the neutralization of acidity through proton consumption. So far, only a handful of moderately acidophilic SRB species have been described, most of which are merely acidotolerant. Here, a novel species within a novel genus of moderately acidophilic SRB is described, Acididesulfobacillus acetoxydans gen. nov. sp. nov. strain INE, able to grow at pH 3.8. Bioreactor studies with strain INE at optimum (5.0) and low (3.9) pH for growth showed that strain INE alkalinized its environment, and that this was more pronounced at lower pH. These studies also showed the capacity of strain INE to completely oxidize organic acids to CO2, which is uncommon among acidophilic SRB. Since organic acids are mainly in their protonated form at low pH, which increases their toxicity, their complete oxidation may be an acid stress resistance mechanism. Comparative proteogenomic and membrane lipid analysis further indicated that the presence of saturated ether-bound lipids in the membrane, and their relative increase at lower pH, was a protection mechanism against acid stress. Interestingly, other canonical acid stress resistance mechanisms, such as a Donnan potential and increased active charge transport, did not appear to be active.

Isolation and characterization of Sphingomonadaceae from fouled membranes.

Membrane filtration systems are widely applied for the production of clean drinking water. However, the accumulation of particles on synthetic membranes leads to fouling. Biological fouling (i.e., biofouling) of reverse osmosis and nanofiltration membranes is difficult to control by existing cleaning procedures. Improved strategies are therefore needed. The bacterial diversity on fouled membranes has been studied, especially to identify bacteria with specialized functions and to develop targeted approaches against these microbes. Previous studies have shown that Sphingomonadaceae are initial membrane colonizers that remain dominant while the biofilm develops. Here, we characterized 21 Sphingomonadaceae isolates, obtained from six different fouled membranes, to determine which physiological traits could contribute to colonization of membrane surfaces. Their growth conditions ranged from temperatures between 8 and 42 oC, salinity between 0.0 and 5.0% w/v NaCl, pH from 4 and 10, and all isolates were able to metabolize a wide range of substrates. The results presented here show that Sphingomonadaceae membrane isolates share many features that are uncommon for other members of the Sphingomonadaceae family: all membrane isolates are motile and their tolerance for different temperatures, salt concentrations, and pH is high. Although relative abundance is an indicator of fitness for a whole group, for the Sphingomonadaceae it does not reveal the specific physiological traits that are required for membrane colonization. This study, therefore, adds to more fundamental insights in membrane biofouling.

Lachnotalea glycerini gen. nov., sp. nov., an anaerobe isolated from a nanofiltration unit treating anoxic groundwater.

A strictly anaerobic bacterium, strain DLD10T, was isolated from a biofilm that developed on a nanofiltration membrane treating anoxic groundwater using glycerol as substrate. Cells were straight to slightly curved rods 0.2-0.5 µm in diameter and 1-3 µm in length, non-motile and non-spore-forming. The optimum temperature and pH for growth were 30 °C and pH 7.0. Strain DLD10T was able to grow in the presence of 0.03-4.5 % (w/v) NaCl. Substrates utilized by strain DLD10T included glycerol and various carbohydrates (glucose, sucrose, fructose, mannose, arabinose, pectin, starch, xylan), which were mainly converted to ethanol, acetate, H2 and formate. Thiosulphate, sulphur and Fe(III) were used as electron acceptors, but sulphate, fumarate and nitrate were not. The predominant membrane fatty acids were C16 : 0, iso-C17 : 1 and C17 : 1ω8c. The DNA G+C content was 36.4 mol%. Strain DLD10T belongs to the family Lachnospiraceae and is distantly related to Clostridium populeti DSM 5832T, Hespellia porcina DSM 15481T and Robinsoniella peoriensis CCUG 48729T (93 % 16S rRNA gene sequence similarity). Physiological characteristics and phylogenetic analysis indicated that strain DLD10T is a representative of a novel species of a new genus, for which the name Lachnotalea glycerini gen. nov., sp. nov. is proposed. The type strain of Lachnotalea glycerini is DLD10T ( = DSM 28816T = JCM 30818T).