Global public health faces a desperate situation, due to the lack of effective antibiotics. Coordinated steps need to be taken, worldwide, to rectify this situation and protect the advances in modern medicine made over the last 100 years. Work at Japan’s Kitasato Institute has been in the vanguard of many such advances, and work is being proactively tailored to promote the discovery of urgently needed antimicrobials. Efforts are being concentrated on actinomycetes, the proven source of most modern antibiotics. We devised a novel physicochemical screening mechanism, whereby simple physico-chemical properties, in conjunction with related detection methods, such as LC/MS, LC/UV, and polarity, could be used to identify or predict new compounds in a culture broth, simply by comparing results with existing databases. New compounds are isolated, purified, and their structure determined before being tested for any bioactivity. We used lyophilized actinomycete strains from the Kitasato Microbial Library, most more than 35 years old, and found 330 strains were producers of useful bioactive substances. We also tested organisms found in fresh samples collected in the complex environments from around plant roots, as well as from sediments of mangrove forests and oceans, resulting in the discovery of 36 novel compounds from 11 actinomycete strains. A compound, designated iminimycin, containing an iminium ion in the structure was discovered from the culture broth of Streptomyces griseus OS-3601, which had been stored for a long time as a streptomycin-producing strain. This represented the first iminium ion discovery in actinomycetes. Compounds with a cyclopentadecane skeleton containing 5,6-dihydro-4-hydroxyl-2-pyrone ring and tetrahydrofuran ring, designated mangromicins, were isolated from the culture broth of Lechevalieria aerocolonigenes K10-0216 obtained from sediment in a mangrove forest. These structures are extremely unique among natural compounds. From the same culture broth, new steroid compounds, named K10-0216 KA and KB, and other new compounds having a thiazole and a pyridine ring, named pyrizomicin A and B, were discovered. New substances can be found from actinomycetes that have been exhaustively studied. Novel compounds with different skeletons can be found from a single broth of one strain. The sought after new antibiotics will arise from continued exploitation of the actinomycetes, especially rare actinomycetes. Work on new organisms and samples should be augmented by re-examination of known actinomycetes already in storage. New research should also be carried out on the manipulation of culture media, thereby stimulating actinomycete strains to produce novel chemicals. The establishment of wide-ranging international research collaborations will facilitate and expedite the efficient and timely discovery and provision of bioactive compounds to help maintain and promote advances in global public health.

In order to facilitate the discovery of novel bioactive compounds from microorganisms, various techniques for isolation of new actinomycete strains have been attempted. Studies of the vertical distribution of actinomycetes in soil, isolation of actinomycetes from desert soils or fallen leaves, selective isolation of Kitasatospora strains using novobiocin or Actinoplanes strains using the chemotactic method, and the use of gellan gum as a solidifying agent were carried out. We discovered 9 novel bioactive compounds from actinomycete strains isolated under unusual conditions, and proposed two new genera, five new species and one new subspecies.

An actinomycete strain 3-44-a(19)T was isolated from sandy soil collected in Bangladesh. The strain formed irregular pseudosporangia directly from aggregated spore chains above the rudimentary aerial mycelium. The pseudosporangia developed singly. Each pseudosporangium contained many small, non-motile, spherical, smooth-surfaced spores in chains. Strain 3-44-a(19)T contained meso- and 3-hydroxydiaminopimelic acid in the cell wall and MK-9(H6) as the major menaquinone and arabinose, galactose, glucose, mannose, ribose and xylose were present in the whole-cell hydrolysate. The diagnostic phospholipid was phosphatidylethanolamine and iso-C15 : 0 (24.6 %), C18 : 1 ω9c (15.5 %), C16 : 0 (10.6 %), C18 : 0 (9.4 %), iso-C16 : 0 (8.6 %) and anteiso-C15 : 0 (6.0 %) were detected as the major cellular fatty acids. The acyl type of the peptidoglycan was glycolyl and mycolic acids were not detected. The G+C content of the DNA was 73.6 mol%. The chemotaxonomic data indicated that the strain belonged to the family Micromonosporaceae. Phylogenetic analysis based on 16S rRNA gene sequence data also suggested that strain 3-44-a(19)T fell within the family Micromonosporaceae. On the basis of phylogenetic analysis and characteristic patterns of 16S rRNA gene signature nucleotides as well as morphological and chemotaxonomic data, this strain should be classified as a member of a new genus and species, Pseudosporangium ferrugineum gen. nov., sp. nov., in the family Micromonosporaceae. The type strain of Pseudosporangium ferrugineum is 3-44-a(19)T (=JCM 14710T =MTCC9007T).

Two novelMicrobacteriumspecies are described on the basis of phenotypic, chemotaxonomic and genotypic studies. The two strains, designated YM10-847^Tand YM11-607^T, were isolated from river sediment and unidentified hydroid, respectively, of a marine lake. The strains were Gram-positive, catalase-positive bacteria withl-ornithine as the diagnostic diamino acid of the peptidoglycan. The acyl type of the peptidoglycan wasN-glycolyl. The major menaquinones were MK-10 and MK-11 for YM10-847^T, and MK-11 and MK-12 for YM11-607^T. Mycolic acids were not detected. The DNA G+C content of strains YM10-847^Tand YM11-607^Twas 67.8 and 71.6 mol%, respectively. Comparative 16S rRNA gene sequence analysis revealed that the two strains belong to the genusMicrobacterium.DNA–DNA relatedness data showed that YM10-847^Tand YM11-607^Tare two novel species of this genus. On the basis of these results, strains YM10-847^Tand YM11-607^Trepresent two novel species of the genusMicrobacterium, for which the namesMicrobacterium sediminicolasp. nov. andMicrobacterium marinilacussp. nov. are proposed. The type strains are YM10-847^T(=MBIC08264^T=DSM 18905^T) and YM11-607^T(=MBIC07778^T=DSM 18904^T), respectively.

Strain KV-657^T was isolated from a paddy field soil sample collected in Japan using GPM agar plates supplemented with catalase. The strain was a Gram-positive, aerobic organism that formed branching hyphae with ll-diaminopimelic acid as the diagnostic peptidoglycan diamino acid. The major menaquinone was MK-8(H₄). Mycolic acids were not detected. The G+C content of the DNA was 70 mol%. 16S rRNA gene sequence analysis revealed that this strain is closely related to Intrasporangium calvum DSM 43043^T, with a similarity of 97.6 %. Based on the morphological, biochemical and chemotaxonomic properties of this strain and phylogenetic analysis, it was concluded that this isolate represents a new genus and species in the family Intrasporangiaceae, for which the name Humihabitans oryzae gen. nov., sp. nov. is proposed. The type strain of Humihabitans oryzae is KV-657^T (=NRRL B-24470^T =NBRC 101802^T).