# Wastewater Treatment with Bacterial Representatives of the _Thiothrix_ Morphotype
## 3 Methods for Identification of _Thiothrix_ in Wastewater Treatment Plants
### Enhanced Biological Removal of Phosphorus
coli_, the synthesis of all types of menaquinones increases under anaerobic conditions and exceeds the total amount of ubiquinone three-fold [102; 103], which makes menaquinone a more likely electron acceptor from MQO under anaerobic conditions. Another notable change in the profile of biosynthesis products induced by anaerbiosis in the six _Thiothrix_ species studied is a 2.4-6.5-fold increase in the expression of the _narG_ gene [104; 105] encoding the catalytic subunit of the dissimilatory nitrate reductase NarGHI anchored in the cytoplasmic membrane. It has been shown that the induction of expression by anaerbiosis is accompanied by an increase in the total activity of nitrate reductase in the cells. Experimental observations on different bacterial species possessing MQO demonstrate good growth rates on acetate and organics at high MQO activity and a significant decrease in growth in MQO deletion mutants in _Corynebacterium glutamicum_[106] and _Pseudomonas aeruginosa_[107], slow growth on fermentable carbon sources and no growth on non-fermentable carbon sources in _Micobacterium stegmatis_[108]. The deletion of _mqo_ in _Mycobacterium tuberculosis_ leads to stress and impairs the survival of the bacterium [109]; in _Pseudomonas fluorescens_, disruptions in the _mqo_ gene led to the loss of the ability to colonize on the root system of tomato [110]. All of the above facts point to an important energetic role of MQO in coupling with nitrate respiration. Although the respiratory chain with Nar enzyme complex as a terminal oxidase and nitrate as an electron acceptor are characterized by lower energetic efficiency as compared to oxygen respiration, the energetic capacity of respiration involving nitrate is comparable to that of the aerobic respiration process (nitrate respiration allows bacteria to transform the energy of substrates into universal energy form with electric potential on the membrane, comparable in magnitude to oxygen respiration). The change in free energy during the oxidation of one molecule of glucose by molecular oxygen (\(\Delta G^{\circ f}=-2870\) kJ/mol) is of the same order as the oxidation of the same substrate under anaerobic conditions by nitrate reduced to nitrite (\(\Delta G^{\circ f}=-1770\) kJ/mol). As shown in a pangenomic study, almost all members of the genus _Thiothrix_, with the exception of '_Ca_. Thiothrix anitrata' A52 and '_Ca_. Thiothrix sulfafinftis' KT, possess the capacity for anaerobic respiration using nitrogen-containing compounds [94], which indicates the high potential of _Thiothrix_ representatives to persist in bioreactors in the anaerobic phase. According to [PERSON] et al., during the long-term operation of the EBPR system with glutamate as the sole source of carbon and nitrogen, the content of members of the genus _Thiothrix_ could be 37%, with _Thiothrix_ members able to participate in phosphorus removal by accumulating poly-P [99]. However, another study showed that although _Thiothrix_ was one of the dominant PAOs at different stages of EBPR bioreactor operation, it was more abundant with propionic acid as the carbon source than when glutamate was used [112]. The use of glycine as a carbon source had an adverse effect on _Thiothrix_ and other PAOs in the EBPR system [96]. It should be noted that the explosive growth of members of the genus _Thiothrix_ leading to unfavorable sludge bulking can be observed in EBPR systems under changes in cultivation conditions, such as stopping the use of the nitrification inhibitor allythiouurea, which is used to stimulate the growth of _Tetrasphaera_-related PAOs [113]. The intensive study of _Thiothrix_ metagenomes in the last decade has revealed the significant potential of the species of this genus to address the challenge of phosphate removal from the environment. In the two genomes of '_Ca_. Thiothrix moscovensis' and  
Figure 6: The role of malate: quinone oxidoreductase (MQO) in _Thiothrix_ metabolism as determined from experimental and genomic data.