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The production of a stable foam on the surfaces of reactors is a global operating problem in activated sludge plants. In many cases, these foams are stabilized by hydrophobic members of the Mycolata, a group of Actinobacteria whose outer membranes contain long-chain hydroxylated mycolic acids. There is currently no single strategy which works for all foams. One attractive approach is to use lytic bacteriophages specific for the foam stabilizing Mycolata population. Such phages are present in activated sludge mixed liquor and can be recovered readily from it. However, no phage has been recovered which lyses Gordonia amarae and Gordonia pseudoamarae, probably the most common foaming Mycolata members. Whole genome sequencing revealed that both G. amarae and G. pseudoamarae from plants around the world are particularly well endowed with genes encoding antiviral defence mechanisms. However, both these populations were lysed rapidly by a parasitic nanobacterium isolated from a plant in Australia. This organism, a member of the Saccharibacteria, was also effective against many other Mycolata, thus providing a potential agent for control of foams stabilized by them., (© 2022 The Society for Applied Microbiology.)

We describe here the isolation and characterization of the bacteriophage, NTR1 from activated sludge. This phage is lytic for Nocardia transvalensis, Nocardia brasiliensis and Nocardia farcinica. NTR1 phage has a genome sequence of 65,275 bp in length, and its closest match is to the Skermania piniformis phage SPI1 sharing over 36% of its genome. The phage belongs to the Siphoviridae family, possessing a long non-contractile tail and icosahedral head. Annotation of the genome reveals 97 putative open reading frames arranged in the characteristic modular organization of Siphoviridae phages and contains a single tRNA-Met gene.

Foaming in activated sludge plants is a worldwide problem commonly caused by proliferation of bacteria of the order Corynebacteriales. These include Skermania piniformis, a filamentous bacterium that has been documented to be a major cause of foaming globally, and particularly in Australian treatment plants. Phage SPI1 is the first phage that was isolated and shown to infect this organism. It targets seven of the nine strains of S. piniformis held in our culture collection, but none of the other 73 mycolata strains of different genera, mostly isolated from wastewater, against which it was tested. Phage SPI1 is a member of the family Siphoviridae and has a circularly permuted dsDNA genome of 55,748 bp with a G+C content of 67.8 mol %. It appears to be obligatorily lytic, with no evidence of genes related to a lysogenic mode of existence.

Three Tsukamurella phages, TIN2, TIN3, and TIN4, were isolated from activated sludge treatment plants located in Victoria, Australia, using conventional enrichment techniques. Illumina and 454 whole-genome sequencing of these Siphoviridae viruses revealed that they had similar genome sequences, ranging in size between 76,268 bp and 76,964 bp. All three phages shared 74% nucleotide sequence identity to the previously described Gordonia phage GTE7. Genome sequencing suggested that phage TIN3 had suffered a mutation in one of its lysis genes compared to the sequence of phage TIN4, to which it is genetically very similar. Mass spectroscopy data showed the unusual presence of a virion structural gene in the DNA replication module of phage TIN4, disrupting the characteristic modular genome architecture of Siphoviridae phages. All three phages appeared highly virulent on strains of Tsukamurella inchonensis and Tsukamurella paurometabola., (Copyright © 2015, American Society for Microbiology. All Rights Reserved.)

We here characterize a novel bacteriophage (NBR1) that is lytic for Nocardia otitidiscaviarum and N. brasiliensis. NBR1 is a member of the family Siphoviridae and appears to have a structurally more complex tail than previously reported Siphoviridae phages. NBR1 has a linear genome of 46,140 bp and a sequence that appears novel when compared to those of other phage sequences in GenBank. Annotation of the genome reveals 68 putative open reading frames. The phage genome organization appears to be similar to other Siphoviridae phage genomes in that it has a modular arrangement.

Rhodococcus equi is a pathogenic member of the Actinobacteria responsible for causing serious infections in equines. A novel Siphoviridae bacteriophage (REQ1) lytic in R. equi was isolated and characterized. The genome size of REQ1 is 51,342 bp, and its sequence shares 7 % similarity to other DNA sequence in GenBank. Putative open reading frames were identified, and their functions were identified based on their predicted amino acid similarities. REQ1 phage has a modular genome, a feature common in double-stranded DNA phages.

The Nosticoida limicola filamentous morphotype is held responsible for incidents of bulking and foaming in activated sludge. Members of the actinobacterial N. limicola II have been isolated and grown in pure culture and shown to belong to the genus Tetrasphaera, and play an important role in phosphorus removal. This article describes the isolation and genomic characterization of a phage able to lyse Tetrasphaera jenkinsii, TJE1. This lytic phage is a member of the Caudovirales specific for T. jenkinsii. The complete DNA sequence of TJE1 phage revealed it to have a circularly permuted genome (49,219 bp) with 66 putative open reading frames, a single transcriptional terminator, and 6 pairs of inverted repeats within the genome sequence. The TJE1 phage genome is organised into a modular gene structure, but shares only limited sequence identity with other phages so far described.

Bacteriophages are considered to be the most abundant biological entities on the planet. The Siphoviridae are the most commonly encountered tailed phages and contain double-stranded DNA with an average genome size of ∼50 kb. This paper describes the isolation from four different activated sludge plants of the phage RRH1, which is polyvalent, lysing five Rhodococcus species. It has a capsid diameter of only ∼43 nm. Whole-genome sequencing of RRH1 revealed a novel circularly permuted DNA sequence (14,270 bp) carrying 20 putative open reading frames. The genome has a modular arrangement, as reported for those of most Siphoviridae phages, but appears to encode only structural proteins and carry a single lysis gene. All genes are transcribed in the same direction. RRH1 has the smallest genome yet of any described functional Siphoviridae phage. We demonstrate that lytic phage can be recovered from transforming naked DNA into its host bacterium, thus making it a potentially useful model for studying gene function in phages.

Most activated sludge treatment plants suffer from the presence of foams on the surfaces of their aeration reactors. These are often stabilized by hydrophobic mycolic acid-synthesizing actinobacterial species. A polyvalent Siphoviridae phage, GTE7, which lysed several Gordonia and Nocardia species, is described here. Its genome has a modular structure similar to that described for Rhodococcus phage ReqiDocB7. In laboratory-scale experiments, we showed that GTE7 prevents stabilization of foams by these Gordonia and Nocardia species.

Hydrophobic Actinobacteria are commonly associated with the stabilization of foams in activated sludge systems. One possible attractive approach to control these foam-stabilizing organisms is the use of specific bacteriophages. We describe the genome characterization of a novel polyvalent DNA phage, GTE2, isolated from activated sludge. This phage is lytic for Gordonia terrae, Rhodococcus globerulus, Rhodococcus erythropolis, Rhodococcus erythropolis, Nocardia otitidiscaviarum, and Nocardia brasiliensis. Phage GTE2 belongs to the family Siphoviridae, possessing a characteristic icosahedral head encapsulating a double-stranded DNA linear genome (45,530 bp) having 10-bp 3'-protruding cohesive ends. The genome sequence is 98% unique at the DNA level and contains 57 putative genes. The genome can be divided into two components, where the first is modular and encodes phage structural proteins and lysis genes. The second is not modular, and the genes harbored there are involved in DNA replication, repair, and metabolism. Some have no known function. GTE2 shows promising results in controlling stable foam production by its host bacteria under laboratory conditions, suggesting that it may prove useful in the field as a biocontrol agent.