Dietary specialization in mutualistic acacia-ants affects relative abundance but not identity of host-associated bacteria.

Acacia-ant mutualists in the genus Pseudomyrmex nest obligately in acacia plants and, as we show through stable isotope analysis, feed at a remarkably low trophic level. Insects with diets such as these sometimes depend on bacterial symbionts for nutritional enrichment. We, therefore, examine the bacterial communities associated with acacia-ants in order to determine whether they host bacterial partners likely to contribute to their nutrition. Despite large differences in trophic position, acacia-ants and related species with generalized diets do not host distinct bacterial taxa. However, we find that a small number of previously undescribed bacterial taxa do differ in relative abundance between acacia-ants and generalists, including several Acetobacteraceae and Nocardiaceae lineages related to common insect associates. Comparisons with an herbivorous generalist, a parasite that feeds on acacias and a mutualistic species with a generalized diet show that trophic level is likely responsible for these small differences in bacterial community structure. While we did not experimentally test for a nutritional benefit to hosts of these bacterial lineages, metagenomic analysis reveals a Bartonella relative with an intact nitrogen-recycling pathway widespread across Pseudomyrmex mutualists and generalists. This taxon may be contributing to nitrogen enrichment of its ant hosts through urease activity and, concordant with an obligately host-associated lifestyle, appears to be experiencing genomewide relaxed selection. The lack of distinctiveness in bacterial communities across trophic level in this group of ants shows a remarkable ability to adjust to varied diets, possibly with assistance from these diverse ant-specific bacterial lineages.

Rubeomycin, a new anthracycline antibiotic complex. I. Taxonomy of producing organism, isolation, characterization and biological activities of rubeomycin A, A1, B and B1.

A new antibiotic complex has been obtained from the cultures of an actinomycete, strain FA-1180, isolated from a soil sample collected at lake side of Biwa in Japan. On the basis of taxonomic studies the producing microorganism is designated as Actinomadura roseoviolacea var. biwakoensis nov. var. The antibiotic complex belongs to the class of anthracycline glycoside antibiotics. All components form deep red fine needles on crystallization; components are named rubeomycin A, A1, B and B1. These components exhibit activity against Gram-positive bacteria as well as Yoshida sarcoma cell in vitro. These components are also effective on P388 leukemia.