Metabolic models based on genomic sequence data from metagenomic libraries and axenic strains of the lipid accumulating filamentous bacterium Candidatus ‘Microthrix parvicella’. Candidatus Neomicrothrix parvicella RN1

Candidatus ‘Microthrix parvicella’ is a lipid accumulating, microaerophilic, psychrotolerant, filamentous bacteria so far found only in activated sludge wastewater treatment plants where it is a common causative agent of sludge separation problems. Despite attracting considerable interest, its detailed physiology are still unclear. When the genome of the RN1 strain was sequenced and annotated it facilitated construction of a theoretical metabolic model based on available in situ and axenic experimental data. This model proposes that under anaerobic conditions this organism accumulates preferentially long chain fatty acids as triacylglycerols which are respired when electron acceptors become available. Utilisation of trehalose and/or polyphosphate stores, or partial oxidation of long chain fatty acids may supply the energy required for anaerobic lipid uptake and storage. Comparing the genome sequence of this isolate with metagenomes from two full-scale wastewater treatment plants reveals high levels of shared sequence similarities, and few metabolic differences. Of those genes assigned a function, such differences are restricted largely to those involved in exopolysaccharide biosynthesis or mobile genetic elements. They also include genes for fructose metabolism and mercury resistance. The genomic information obtained here will provide the basis for future research into in situ gene expression and regulation, and give unparalleled insight into the ecophysiology of this unusual and biotechnologically important filamentous bacterium.