A novel locus for mycelial aggregation forms a gateway to improved Streptomyces cell factories

Abstract

BackgroundStreptomycetes produce a plethora of natural products including antibiotics and anticancer drugs, as well as many industrial enzymes. Their mycelial life style is a major bottleneck for industrial exploitation and over decades strain improvement programs have selected production strains with better growth properties. Uncovering the nature of the underlying mutations should allow the ready transfer of desirable traits to other production hosts.ResultsHere we report that the mat gene cluster, which was identified through reverse engineering of a non-pelleting mutant selected in a chemostat, is key to pellet formation of Streptomyces lividans. Deletion of matA or matB, which encode putative polysaccharide synthases, effects mycelial metamorphosis, with very small and open mycelia. Growth rate and productivity of the matAB null mutant were increased by over 60% as compared to the wild-type strain.ConclusionHere, we present a way to counteract pellet formation by streptomycetes, which is one of the major bottlenecks in their industrial application. The mat locus is an ideal target for rational strain design approaches aimed at improving streptomycetes as industrial production hosts.Electronic supplementary materialThe online version of this article (doi:10.1186/s12934-015-0224-6) contains supplementary material, which is available to authorized users.

Taxonomy, Physiology, and Natural Products of Actinobacteria

“…A novel set of genes was recently discovered in Streptomyces that control pellet growth, called mat, for mycelial aggregation (387). The genes were discovered 30 years ago via reverse engineering of a strain of S. lividans that was selected for fragmented growth in a chemostat (388).…”

“…The genes were discovered 30 years ago via reverse engineering of a strain of S. lividans that was selected for fragmented growth in a chemostat (388). Deletion of the mat genes (SCO2962 and SCO2963 in S. coelicolor) prevented pellet formation and increased both growth rate and enzyme production in S. lividans (387). The mat genes are probably responsible for the production of a secreted polysaccharide, which presumably glues the hyphae together and thus promotes pellet aggregation.…”

Aggregation of germlings is a major contributing factor towards mycelial heterogeneity of Streptomyces

“…These include among others the recently discovered mat genes11, as well as cslA, glxA and dtpA 121314. The common feature of these genes is that they encode proteins that are involved in the synthesis of extracellular glycans.…”

Recent advances in understanding Streptomyces

“…Continued hyphal elongation is co-ordinated by the DivIVA-based polarisome 50 and (in addition to cell wall growth) involves the extracellular production of cellulose-like glycan catalysed by polarisome-linked ClsA (cellulose synthase-like) associated with the copper oxidase GlxA 52, 53 . MatAB proteins have an uncharacterised role in glycan production 54 . Vesicular membrane structures form in apparently irregular locations within hyphae, and some of them extend across the hyphal compartment, separating nucleoids 57, 58 .…”

“…Like ClsA, GlxA is tip-located at least at some growth stages 53 , though the two proteins have not been analysed together. The synthesis of extracellular polysaccharides soon after germination, under the control of clsA , glxA , and the newly identified locus matAB , is responsible for the aggregation of germlings, leading to the formation of mycelial clumps in submerged culture, a well-known problem in industrial fermentations 54, 55 .…”