Bacterial control of Agromyces ramosus in soil

Abstract

Agromyces ramosus occurs in high numbers in many soils. It also is a known predator of various gram-positive and gram-negative soil bacteria, including Azotobacter vinelandii. Based on this, it would seem that, in natural soil, A. ramosus should control the population sizes of these soil bacteria. As a partial test of this assumption, we examined the possibility that soil might contain other bacterial predators that could hold A. ramosus in check. Three gram-negative bacterial predators of A. ramosus were isolated from soil. When one of these predators, strain N-1, was added to natural soil, it exhibited an attack – counter attack phenomenon in its interactions with A. ramosus. The indigenous A. ramosus cells in soil, or added A. ramosus cells, produced mycelium that approached, then lysed, approximately one-third of the N-1 cells. The surviving N-1 cells, however, then proceeded to lyse the A. ramosus mycelium, but not the rod-form cells that had fragmented from the mycelium. Strain N-1 then multiplied. This sequence also occurred if Azotobacter vinelandii was added with A. ramosus to soil, either with or without addition of N-1 cells. N-1 attacked the A. ramosus mycelium that was attacking Azotobacter vinelandii. In soil and with pure cultures in the laboratory, the dormant rod-form cells of A. ramosus that fragmented from the mycelium were not attacked. A growth initiation factor seemed to be involved in the attack – counter attack relationship of N-1 and A. ramosus. Strain N-1 and the other two gram-negative predators mentioned above could attack a variety of bacterial species in soil, in addition to A. ramosus which in itself is a predator. Thus, some sort of hierarchy of bacterial predation seems to exist in soil.

Taxonomy of the genus Cupriavidus: a tale of lost and found

“…In conformity with Rules 15, 17, 23a and 37a (1) Cupriavidus necator was described by Makkar & Casida (1987) to accommodate a non-obligate bacterial predator of various Gram-negative and Gram-positive soil bacteria and fungi (Byrd et al, 1985;Sillman & Casida, 1986;Zeph & Casida, 1986). The single known isolate, strain N-1 T (=LMG 8453 T ), was obtained from soil in the vicinity of University Park, PA, USA.…”

Cupriavidus

“…The cells decrease somewhat in size and become more rounded as cultures age, or when the organism is placed in contact with soil during soil column studies (Byrd et al, 1985). In soil, the rounded forms of C. necator appear to be dormant (Byrd et al, 1985). C. necator reproduces by binary fission and is motile by 2-10 peritrichous flagella.…”

“…C. necator produces the heat-labile, magnesium-related growth initiation factor (GIF) that was first described by Casida (1984) and that is produced by various types of bacteria in soils. This GIF can initiate the growth of Agromyces ramosus and other species in soil (Casida, 1984;Byrd et al, 1985), thereby increasing the supply of suitable prey cells for nonobligate bacterial predators like C. necator. The actual mechanism by which C. necator kills its prey cells is not yet known, although Casida (1987) has suggested that a copper-related peptide used to scavenge copper from the environment (see below) might also be used to deliver excess (and toxic) amounts of copper to prey cells.…”

“…(see Byrd et al, 1985) to assess the ability of C. necator and several other nonobligate bacterial predators to attack various types of potential prey species in soil. Of the 11 predators examined, C. necator strain N-1 (the type strain) and an uncharacterized predator strain (designated L-2) were capable of attacking the widest variety of prey species.…”

“…When C. necator interacts with Agromyces ramosus in a soil, a predator-on-predator attack and counterattack phenomenon occurs (Byrd et al, 1985). A. ramosus is a Gram-positive species that occurs in high numbers in soils and functions as a nonobligatory predator that destroys cells of several other bacterial species.…”