Even Assad has to now take ISIS more seriously than he did before when he bribed them to leave him alone

Iraq Shia militiamen deployed to Damascus to guard the revered Sayyida Zeinab shrine — along with Iranian revolutionary guards - are soon likely to be protecting the Shia holy places of Najaf and Karbala from Isis and other Sunni groups seeking to ignite a sectarian civil war. Many are with the Iraqi militia Asaib Ahl al-Haq, (League of the Righteous), an Iranian-backed force that is expected to spearhead the fightback against Isis. Men from the Lebanese Shia movement Hezbollah are filling the vacuum in Syria.
In another twist in the fast-moving situation, last weekend the Syrian air force staged its first raids on Isis bases in Raqqa, Hassakeh and Deir al-Zor. That was noteworthy because Assad's enemies have often accused him of tolerating Isis or tacitly cooperating with it in order to split rebel ranks and present himself as a secular bulwark against al-Qaida and jihadi fanaticism.
According to reports from Raqqa, Isis fighters inexplicably left their barracks 24 hours before the attack. In Deir al-Zor, planes seemed to fly in and out of Iraqi airspace, perhaps suggesting collaboration with Baghdad.
The Syrian National Coalition, the main western-backed opposition group, quickly dismissed the raids as "a ridiculous decoy". Assad, it claimed, "aims through this fake air strike against limited Isis administrative centres to send a message to the international community and to rebuild trust with it, after its close relationship with Isis was exposed".
Another more straightforward explanation, however, could be that developments in Iraq have forced the Syrian president to take the jihadis far more seriously than he appears to have done so far.

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Isis breach of Iraq-Syria border merges two wars into one 'nightmarish reality'

In the past Assad was able to "Bribe" ISIS (ISIL) into leaving him alone and even have them fight more moderate Sunni Rebels so he wouldn't have to. However, now Assad realizes ISIS threatens not only his Syria but also Iraq in ever more horrifying ways for him, especially as Sunnis from all over the region flock to ISIS seeing the weakness in Assad and Iraq and wanting to drive  all Shias to extinction now through ISIS. In Sheer numbers the Sunnis likely could extinct Shias in the Middle East. However, this is why Iran needs nuclear weapons to counter this existential threat that is here right now for them to deal with in reality at present.