Acetoin production enhanced by manipulating carbon flux in a newly isolated Bacillus amyloliquefaciens.

Many readers of this journal will need no introduction to the bacterial genus Streptomyces, which includes several hundred species, many of which produce biotechnologically useful secondary metabolites. The last 2 years have seen numerous publications describing Streptomyces genome sequences (Table ​(Table1),1), mostly as short genome announcements restricted to just 500 words and therefore allowing little description and analysis. Our aim in this current manuscript is to survey these recent publications and to dig a little deeper where appropriate. The genus Streptomyces is now one of the most highly sequenced, with 19 finished genomic sequences (Table ​(Table2)2) and a further 125 draft assemblies available in the GenBank database as of 3rd of May 2014; by the time this is published, no doubt there will be more. The reasons given for sequencing this latest crop of Streptomyces include production of industrially important enzymes, degradation of lignin, antibiotic production, rapid growth and halo-tolerance and an endophytic lifestyle (Table ​(Table11).



Table 1

Recent genome publications (2013 and 2014) for Streptomyces species





Table 2

Completely sequenced Streptomyces species genome sequences available in GenBank as of 29 April 2014




Mining genomes for secondary metabolism gene clusters
Given the strong emphasis on secondary metabolism in Streptomyces genomics research, it is timely that version 2.0 of antiSMASH has been released and published (Blin et al., 2013). This computational tool has become a de facto standard for mining secondary metabolism gene clusters in genome sequences. Version 2.0 is completely revamped and, significantly, can now be used with highly fragmented draft-quality genome sequences whereas the previous version only worked well with finished genomes. Clearly, this is of immense importance to the discovery of novel metabolites in the ever-expanding database of streptomycete draft-quality genome sequences. For example, antiSMASH 2.0 analysis of the Streptomyces roseochromogenes subsp. oscitans DS 12.976 genome sequence revealed 43 new gene clusters in addition to recovering the already known clorobiocin gene cluster (Ruckert et al., 2014).

The genome sequence of Streptomyces gancidicus strain BKS 13–15 was published before antiSMASH 2.0 became available. The authors state that seven genes mapped on to the streptomycin biosynthesis pathway based on gene-by-gene sequence similarities (Kumar et al., 2013) against homologues of genes in KEGG pathways (Kanehisa et al., 2012). However, we found no bioinformatic evidence for a streptomycin biosynthesis pathway encoded in this genome, although our antiSMASH 2.0 search did find 38 putative gene clusters. In common with many other pathways for secondary metabolism, genes for production of the aminoglycoside streptomycin are organized into a cluster of contiguous genes. The nucleotide sequences of at least two such clusters are available (GenBank accessions {"type":"entrez-nucleotide","attrs":{"text":"GU384160","term_id":"288549237","term_text":"GU384160"}}GU384160 and {"type":"entrez-nucleotide","attrs":{"text":"AJ862840","term_id":"62896300","term_text":"AJ862840"}}AJ862840 from Streptomyces platensis and Streptomyces griseus respectively). Our blastn searches (using these two cluster sequences as queries) failed to detect a complete streptomycin gene cluster in the S. gancidicus genome, but there were some regions of sequence similarity on a 111 kb contig (GenBank: {"type":"entrez-nucleotide","attrs":{"text":"AOHP01000057","term_id":"455649599","term_text":"AOHP01000057"}}AOHP01000057). An antiSMASH 2.0 search failed to find any aminoglycoside biosynthetic cluster in this genome. We are not aware of any experimental evidence that this strain produces the aminoglycoside streptomycin and conclude that these seven genes highlighted by the authors (Kumar et al., 2013) most probably encode components of another, perhaps novel, pathway. This illustrates the value of the antiSMASH 2.0 tool, which has the potential to discover new pathways, rather than relying on similarity to the pathways already represented in the KEGG database (and therefore, by definition, not novel).

The case of Streptomyces species strain Mg1 (Hoefler et al., 2013) illustrates another consideration when mining bacterial genome sequences for secondary metabolism gene clusters. Many of the recently published Streptomyces genome sequences are assembled from massively parallel sequencing platforms such as 454 GS-FLX and Illumina HiSeq. The short sequence reads (typically less than 450 bp) and relatively high error rates associated with these platforms can lead to rather fragmented and/or incomplete genome assemblies. The situation is not helped by the biased sequence composition (approximately 70% G + C) of Streptomyces DNA. Furthermore, non-ribosomal peptide synthases (NRPS) and polyketide synthetases (PK) are long, modular proteins made up of many repeated domain units. This means that the genes encoding these key enzymes can be particularly difficult to assemble accurately from short sequence reads. To overcome this issue, the authors of the Mg1 genome project (Hoefler et al., 2013) exploited the PacBio SMRT sequencing technology, which provides sequences reads of several Kb in length, meaning that an entire PK or NRPS gene could be represented on a single sequence read, thus avoiding the difficulties of assembling repetitive sequence from short fragments. They also generated an assembly of the same genome based on 454 GS-FLX and Illumina HiSeq. The results were striking: more than 90% of the genome was represented in a single contig of 7.8 Mb in the PacBio-based assembly and the PacBio-based assembly was 19.9% longer than the 454/Illumina-based one (8 705 754 versus 7 260 368 bp). As the authors point out, this implies that more than 1 Mb of sequence in the PacBio-based assembly is missing from the 454/Illumina-based one, as can be seen in Fig. ​Fig.1A.1A. However, the 454/Illumina-based assembly is not simply a subset of the PacBio-based one; as illustrated in Fig. ​Fig.1B,1B, a substantial portion of the 454/Illumina-based assembly is missing from the PacBio assembly. Although it is by no means certain which assembly is more ‘correct’, it might be possible to generate a more complete genome assembly by reconciling the two different assemblies.



Figure 1

Comparison of two different genome assemblies for Streptomyces strain Mg1, one based on PacBio sequence data and the other based on 454 and Illumina sequence data. A illustrates alignment of both the assemblies against the PacBio-based assembly. B illustrates ...



Fragmentation and incompleteness of a genome assembly has implications for discovery of secondary metabolism gene clusters. In Fig. ​Fig.1C,1C, we show a putative NRPS gene cluster detected apparently intact in a single contig of the PacBio-based sequence assembly identified by antiSMASH 2.0. Searching the 454/Illumina-based assembly reveals two incomplete fragments of the gene cluster, lying on two different contigs, and with part of the cluster apparently absent. Although we should be cautious about extrapolating too much from this single anecdotal example, the evidence suggests that longer read lengths can be very valuable in genome mining for secondary metabolism clusters.

https://sfamjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/1751-7915.12143

Recently published Streptomyces genome sequences

The microbial secondary metabolites have great importance for humans and agriculture. They are widely used as active drug ingredients in medicine (e.g., many antibiotics, antitumor agents, and antivirals are derived from secondary metabolites, as are antipyretics like aspirin, hallucinogenics like LSD, and cholesterol-lowering drugs like lovastatin), as herbicides or phytotoxins in agriculture, and as food additives (color, flavors, and sweeteners), fragrances, and even as precursors for the synthesis of plastics. Biotechnology has opened up new possibilities for potential applications of beneficial microbiomes producing secondary metabolites in agriculture, industrial, pharmaceuticals, and allied sectors. The microbes from diverse habitats including plant microbiomes (epiphytic, endophytic rhizospheric) and extreme microbiomes (psychrophilic, thermophilic, acidophilic, alkaliphilic, xerophilic, and halophilic) produce the necessary secondary metabolites for diverse applications. The present book chapter provides complete, comprehensive, and broad subject-based reviews on existing microbial biodiversity with the production of potential secondary metabolites for different biotechnological applications. Here we have also discussed metabolic engineering for the production of secondary metabolites from different groups of microbes including archaea, bacteria, and eukarya and their applications in agriculture, medicine, and industry.

Metabolic Engineering to Synthetic Biology of Secondary Metabolites Production

We have determined the time-resolved transcriptome of the model gram-positive organism B. subtilis during growth in a batch fermentor on rich medium. DNA microarrays were used to monitor gene transcription using 10-minute intervals at 40 consecutive time points. From the growth curve and analysis of all gene expression levels, we identified 4 distinct growth phases and one clear transition point: a lag phase, an exponential growth phase, the transition point and the very clearly separated early and late stationary growth phases. The gene expression profiles suggest the occurrence of stress responses at specific times although no external stresses were applied. The first one is a small induction of the SigB regulon that occurs at the transition point. Remarkably, a very strong response is observed for the SigW regulon, which is highly upregulated at the onset of the late stationary phase. Bioinformatic analyses that were performed on our data set suggest several novel putative motifs for regulator binding. In addition, the expression profiles of several genes appeared to correlate with the oxygen concentration. This data set of the expression profiles of all B. subtilis genes during the entire growth curve on rich medium constitutes a rich repository that can be further mined by the scientific community.

/pdf/time-resolved-transcriptomics-and-bioinformatic-analyses-1tj1in6pi3.pdf

Time-Resolved Transcriptomics and Bioinformatic Analyses Reveal Intrinsic Stress Responses during Batch Culture of Bacillus subtilis

Elaeis guineensis as a tropical oil-crop is particularly sensitive to low temperature. Improvement of cold-tolerance may significantly increase the total cultivation area of this tropical oil-crop worldwide. We sequenced cold-treated and control (untreated) samples of Elaeis guineensis. De novo assembly generated 51,452 unigenes with an average length of 703 bp. Subsequently, these expressed sequences were functionally annotated. In the K category (transcription factors) of COG (Cluster of Orthologous Group) annotation, the largest proportion of genes induced and repressed at least two-fold under cold stress were from the AP2/ERE family, indicating that C-repeat binding factor, (CBFs, members of the AP2/ERE family) may play a central role in cold tolerance in Elaeis guineensis. Subsequently, the CBF-mediated signal transduction pathway was reconstructed based on transcriptome data and the gene expression profile involving the pathway was examined using real-time quantitative RT-PCR (qRT-PCR). CBFs reached maximum transcript level both at medium (4 h) and long period time points (7 days), contrary to the expression pattern of CBFs in Arabidopsis and rice. Moreover, the promoters of downstream Cold Responsive gene (CORs) regulated by CBFs were analyzed. Conservation, mutation and absence of the DRE core motif were detected in the promoters of six CORs. These mutations in DRE motifs suggest that CORs may not be induced via cold stress in Elaeis guineensis.

/pdf/rna-seq-analysis-of-oil-palm-under-cold-stress-reveals-a-1nyy2gs4u4.pdf

RNA-Seq Analysis of Oil Palm under Cold Stress Reveals a Different C-Repeat Binding Factor (CBF) Mediated Gene Expression Pattern in Elaeis guineensis Compared to Other Species

Dissolved oxygen (DO) is an important factor for adenosine fermentation. Our previous experiments have shown that low oxygen supply in the growth period was optimal for high adenosine yield. Herein, to better understand the link between oxygen supply and adenosine productivity in B. subtilis (ATCC21616), we sought to systematically explore the effect of DO on genetic regulation and metabolism through transcriptome analysis. The microarrays representing 4,106 genes were used to study temporal transcript profiles of B. subtilis fermentation in response to high oxygen supply (agitation 700 r/min) and low oxygen supply (agitation 450 r/min). The transcriptome data analysis revealed that low oxygen supply has three major effects on metabolism: enhance carbon metabolism (glucose metabolism, pyruvate metabolism and carbon overflow), inhibit degradation of nitrogen sources (glutamate family amino acids and xanthine) and purine synthesis. Inhibition of xanthine degradation was the reason that low oxygen supply enhanced adenosine production. These provide us with potential targets, which can be modified to achieve higher adenosine yield. Expression of genes involved in energy, cell type differentiation, protein synthesis was also influenced by oxygen supply. These results provided new insights into the relationship between oxygen supply and metabolism.

/pdf/comparative-transcriptome-analysis-of-bacillus-subtilis-pv5n360cwk.pdf

Comparative transcriptome analysis of Bacillus subtilis responding to dissolved oxygen in adenosine fermentation.

Saccharopolyspora erythraea is a Gram-positive bacterium that can produce antibiotics. However, this microorganism must often be genetically improved for higher production before it can be used in an industrial setting. Here, we report the whole-genome sequence of the industrial hyperproducer strong mutator Saccharopolyspora erythraea strain D.

Shu-Hong Gao

Papers

Comparative transcriptome analysis of Bacillus subtilis responding to dissolved oxygen in adenosine fermentation.

Genome Sequence of Saccharopolyspora erythraea D, a Hyperproducer of Erythromycin