Insect symbionts as valuable grist for the biotechnological mill: an alkaliphilic silkworm gut bacterium for efficient lactic acid production
Insects constitute the most abundant and diverse animal class and act as hosts to an extraordinary variety of symbiotic microorganisms. These microbes living inside the insects play critical roles in host biology and are also valuable bioresources. Enterococcus mundtii EMB156, isolated from the larval gut (gut pH >10) of the model organism Bombyx mori (Lepidoptera: Bombycidae), efficiently produces lactic acid, an important metabolite for industrial production of bioplastic materials. E. mundtii EMB156 grows well under alkaline conditions and stably converts various carbon sources into lactic acid, offering advantages in downstream fermentative processes. High-yield lactic acid production can be achieved by the strain EMB156 from renewable biomass substrates under alkaline pretreatments. Single-molecule real-time (SMRT) sequencing technology revealed its 3.01 Mbp whole genome sequence. A total of 2956 protein-coding sequences, 65 tRNA genes, and 6 rRNA operons were predicted in the EMB156 chromosome. Remarkable genomic features responsible for lactic acid fermentation included key enzymes involved in the pentose phosphate (PP)/glycolytic pathway, and an alpha amylase and xylose isomerase were characterized in EMB156. This genomic information coincides with the phenotype of E. mundtii EMB156, reflecting its metabolic flexibility in efficient lactate fermentation, and established a foundation for future biotechnological application. Interestingly, enzyme activities of amylase were quite stable in high-pH broths, indicating a possible mechanism for strong EMB156 growth in an alkaline environment, thereby facilitating lactic acid production. Together, these findings implied that valuable lactic acid-producing bacteria can be discovered efficiently by screening under the extremely alkaline conditions, as exemplified by gut microbial symbionts of Lepidoptera insects.
KeywordsBombyx mori Gut symbiont Enterococcus mundtii Lactic acid Bioplastic Complete genome sequence
We thank Peter Humphrey for critical read of the manuscript and editorial assistance.
Compliance with ethical standards
Conflict of interest
The authors declare no conflict of interest.
This article does not contain any studies with human participants or animals (except invertebrates, which are exempt from ethical concerns) performed by any of the authors.
- Abdel-Rahman MA, Tashiro Y, Zendo T, Hanada K, Shibata K, Sonomoto K (2011a) Efficient homofermentative L-(+)-lactic acid production from xylose by a novel lactic acid bacterium, Enterococcus mundtii QU 25. Appl Environ Microbiol 77(5):1892–1895. https://doi.org/10.1128/AEM.02076-10 CrossRefPubMedGoogle Scholar
- Abdel-Rahman MA, Tashiro Y, Zendo T, Shibata K, Sonomoto K (2011b) Isolation and characterisation of lactic acid bacterium for effective fermentation of cellobiose into optically pure homo L-(+)-lactic acid. Appl Microbiol Biotechnol 89(4):1039–1049. https://doi.org/10.1007/s00253-010-2986-4 CrossRefPubMedGoogle Scholar
- Ashburner M, Ball CA, Blake JA, Botstein D, Butler H, Cherry JM, Davis AP, Dolinski K, Dwight SS, Eppig JT, Harris MA, Hill DP, Issel-Tarver L, Kasarskis A, Lewis S, Matese JC, Richardson JE, Ringwald M, Rubin GM, Sherlock G (2000) Gene ontology: tool for the unification of biology. The gene ontology consortium. Nat Genet 25(1):25–29. https://doi.org/10.1038/75556 CrossRefPubMedPubMedCentralGoogle Scholar
- Chen B, Sun C, Liang X, Lu X, Gao Q, Alonso-Pernas P, Teh BS, Novoselov AL, Boland W, Shao Y (2016a) Draft genome sequence of Enterococcus mundtii SL 16, an indigenous gut bacterium of the polyphagous Pest Spodoptera littoralis. Front Microbiol 7:1676. https://doi.org/10.3389/fmicb.2016.01676 PubMedPubMedCentralGoogle Scholar
- Eichinger V, Nussbaumer T, Platzer A, Jehl MA, Arnold R, Rattei T (2016) EffectiveDB—updates and novel features for a better annotation of bacterial secreted proteins and type III, IV, VI secretion systems. Nucleic Acids Res 44(D1):D669–D674. https://doi.org/10.1093/nar/gkv1269 CrossRefPubMedGoogle Scholar
- Medema MH, Blin K, Cimermancic P, de Jager V, Zakrzewski P, Fischbach MA, Weber T, Takano E, Breitling R (2011) antiSMASH: rapid identification, annotation and analysis of secondary metabolite biosynthesis gene clusters in bacterial and fungal genome sequences. Nucleic Acids Res 39(Web Server issue):W339–W346. https://doi.org/10.1093/nar/gkr466 CrossRefPubMedPubMedCentralGoogle Scholar
- Schoenian I, Spiteller M, Ghaste M, Wirth R, Herz H, Spiteller D (2011) Chemical basis of the synergism and antagonism in microbial communities in the nests of leaf-cutting ants. Proc Natl Acad Sci U S A 108(5):1955–1960. https://doi.org/10.1073/pnas.1008441108 CrossRefPubMedPubMedCentralGoogle Scholar
- Shi W, Xie S, Chen X, Sun S, Zhou X, Liu L, Gao P, Kyrpides NC, No EG, Yuan JS (2013) Comparative genomic analysis of the microbiome [corrected] of herbivorous insects reveals eco-environmental adaptations: biotechnology applications. PLoS Genet 9(1):e1003131. https://doi.org/10.1371/journal.pgen.1003131 CrossRefPubMedPubMedCentralGoogle Scholar
- Shiwa Y, Yanase H, Hirose Y, Satomi S, Araya-Kojima T, Watanabe S, Zendo T, Chibazakura T, Shimizu-Kadota M, Yoshikawa H, Sonomoto K (2014) Complete genome sequence of Enterococcus mundtii QU 25, an efficient L-(+)-lactic acid-producing bacterium. DNA Res 21(4):369–377. https://doi.org/10.1093/dnares/dsu003 CrossRefPubMedPubMedCentralGoogle Scholar
- Sun Z, Kumar D, Cao G, Zhu L, Liu B, Zhu M, Liang Z, Kuang S, Chen F, Feng Y, Hu X, Xue R, Gong C (2017) Effects of transient high temperature treatment on the intestinal flora of the silkworm Bombyx mori. Sci Rep 7(1):3349. https://doi.org/10.1038/s41598-017-03565-4 CrossRefPubMedPubMedCentralGoogle Scholar
- Tatusov RL, Fedorova ND, Jackson JD, Jacobs AR, Kiryutin B, Koonin EV, Krylov DM, Mazumder R, Mekhedov SL, Nikolskaya AN, Rao BS, Smirnov S, Sverdlov AV, Vasudevan S, Wolf YI, Yin JJ, Natale DA (2003) The COG database: an updated version includes eukaryotes. BMC Bioinform 4:41. https://doi.org/10.1186/1471-2105-4-41 CrossRefGoogle Scholar
- Unban K, Kanpiengjai A, Takata G, Uechi K, Lee WC, Khanongnuch C (2017) Amylolytic enzymes acquired from L-lactic acid producing Enterococcus faecium K-1 and improvement of direct lactic acid production from cassava starch. Appl Biochem Biotechnol 183(1):155–170. https://doi.org/10.1007/s12010-017-2436-1 CrossRefPubMedGoogle Scholar