async def increment_otu_version(db, otu_id: str) -> dict:
    """
    Increment the `version` field by one for the OTU identified by `otu_id`.

    :param db: the application database client
    :param otu_id: the ID of the OTU whose version should be increased
    :return: the updated OTU document

    """
    return await db.otus.find_one_and_update({"_id": otu_id}, {
        "$set": {
            "verified": False
        },
        "$inc": {
            "version": 1
        }
    })