Growing in Saltwater: Biotechnological Potential of Novel Methylotuvimicrobium- and Methylomarinum-like Methanotrophic Bacteria

Methanotrophic bacteria that possess a unique ability of using methane as a sole source of carbon and energy have attracted considerable attention as potential producers of a single-cell protein. So far, this biotechnology implied using freshwater methanotrophs, although many regions of the world have limited freshwater resources. This study aimed at searching for novel methanotrophs capable of fast growth in saltwater comparable in composition with seawater. A methane-oxidizing microbial consortium containing Methylomarinum- and Methylotuvimicrobium-like methanotrophs was enriched from sediment from the river Chernavka (water pH 7.5, total salt content 30 g L-1), a tributary river of the hypersaline Lake Elton, southern Russia. This microbial consortium, designated Ch1, demonstrated stable growth on natural gas in a bioreactor in media with a total salt content of 23 to 35.9 g L-1 at a dilution rate of 0.19-0.21 h(-1). The highest biomass yield of 5.8 g cell dry weight (CDW)/L with a protein content of 63% was obtained during continuous cultivation of the consortium Ch1 in a medium with a total salt content of 29 g L-1. Isolation attempts resulted in obtaining a pure culture of methanotrophic bacteria, strain Ch1(-1). The 16S rRNA gene sequence of strain Ch1(-1) displayed 97.09-97.24% similarity to the corresponding gene fragments of characterized representatives of Methylomarinum vadi, methanotrophs isolated from marine habitats. The genome of strain Ch1(-1) was 4.8 Mb in size and encoded 3 rRNA operons, and about 4400 proteins. The genome contained the gene cluster coding for ectoine biosynthesis, which explains the ability of strain Ch1(-1) to tolerate high salt concentration.

Automated summary

This study identified a novel methanotrophic bacteria capable of fast growth in saltwater, providing a new option for potential production of single-cell protein. The microbial consortium demonstrated stable growth in high salt concentration and achieved high biomass yield and protein content. Isolation attempts resulted in obtaining a pure culture of a salt-tolerant methanotrophic bacteria with a genome containing gene clusters explaining its ability to tolerate high salt concentration.